WHEAT STUDIES OF THE FOOD RESEARCH INSTITUTE

VOL. XII, NO. 6 (Price $.50) FEBRUARY 1936

THE STALE-BREAD PROBLEM

HE staling of bread is a serious burden to bakers. This T WHEAT STUDY is devoted to the critical examination of existing information on the aging of bread. The crust is drier than the crumb and abstracts moisture from inside the loaf. In consequence, it becomes soft and tough. When bread is freshened by warming, the process is reversed, and the crust becomes crisp again. The crust effectively insulates the crumb which becomes stale before losing much moisture. The sol­ uble-starch content of the crumb diminishes and the starch granules become opaque and harder. When bread is fresh­ ened, the change in the starch granules is reversed.

So far, all investigators are agreed. Some believe the change in the starch is a chemical one and make staling depend solely upon the change in the starch. They assume at the same time a transfer of moisture from the starch to the gluten. They re­ gard both processes as reversed when the loaf is freshened by warming. However, there is no conclusive evidence of such a transfer of moisture. It is possible to explain many of the phenomena by merely assuming that, like other jellies, the starch hardens as it sets and softens as it is warmed up again without chemical change. Moreover, it has not been proven that change in the starch is the sole cause of staleness, for there is reason to believe that particularly well-made bread may seem fresh even though the starch has changed ap­ preciably. The study further presents the methods that have been recommended to produce bread that keeps well and the eonditions of storage that tend to keep it fresh.

STANFORD UNIVERSITY, CALIFORNIA February 1936 WHEAT STUDIES OF THE FOOD RESEARCH INSTITUTE Entered as second-class matter February 11, 1925, at the Post Office at Palo Alto, Stanford University Branch, California, under the Act of August 24, 1912. Published ten times a year by Stanford University for the Food Research Insti­ tute. Copyright 1936, by the Board of Trustees of the Leland Stanford Junior University. THE STALE-BREAD PROBLEM

away. There are, however, not a few places ECONOMIC AND SOCIAL CONSIDERATIONS where the volume of stale bread is so great it When bread was baked at home or by the cannot be disposed of in this way but has to ncighborhood or village baker, stale bread be sold for animal feed or even used for fuel. presented neither social nor economic prob­ Where these practices occur, there is needless lems, for it was possible to adjust production waste of food and, in the long run, the price to demand with considerable exactness. There of bread to the consumer tends to be raised. was little stale bread and what there was could Before the war, even among bakeries gen­ be used for food purposes as such, or in the erally recognized as efficient, stale - bread baking of cakes or of spe- losses of 6 to 10 per cent of cial types of bread like production were common, brown bread, or in cookery CONTENTS and exceptional cases of as bread crumbs. Under PAGE much higher losses, run­ Economic and Social Con- modern conditions, when siderations ...... 221 ning for brief periods as bread is manufactured in Structure and Behavior of high as 25 per cent of the rather large factories! and Starch Grains ...... 225 bread baked, admittedly distributed over a wide Manifestations of Staleness .. 232 occurred. In November territory round about each History of Bread - Staling 1917, the United States such bakery, the adjust­ Theories ...... 234 Food Administration esti­ Critique of Competing Hy- ment of production to de­ potheses ...... 240 mated that loss from re­ mand is often quite imper­ Prolonging the Life of Bread 243 turn of stale bread amount­ fect. The serious losses, Food Value of Fresh and of ed to "upwards of 600,000 which have developed in Slale Bread...... 246 barrels" of flour a year,8 the form of large daily ac- equivalent to about 2.7 cumulations of stale bread million bushels of wheat. that cut into the baker's profits because un­ During the war most European nations salable at the standard price, constitute one faced the danger of wheat shortage. Their of his most serious problems.2 problem was not so much to prevent waste Large stale-bread losses tend to raise the as to curtail consumption of wheat products. price of fresh bread to consumers, since the One of the ways by which it was sought to stale loaves are sold at a price about cover­ limit bread consumption was to forbid the ing the cost of materials or are used in var­ sale of fresh bread on the assumption that ious ways in the form of crumbs. The baker stale bread, being less palatable than fresh, must find compensation in the price of fresh would be consumed in smaller amounts. The bread. Where this practice prevails, no great British Ministry of Food, for example, forbade economic waste is involved, and the mean the sale of bread within 12 hours after baking. price of bread to the consumer not much But neither bakers nor consumers would con­ affected. The poor and others, for example sent to have the regulations continued in charitable institutions, receive bread at a low times of peace. Without such restrictions, price. Some bakers even give their stale bread bakers are always at pains to increase the consumption of bakers' bread rather than to 1 C. 1. Aisberg, Combination in the American Bread­ see it reduced; and, for this purpose, few Baking Industry, with Some Observations on the Mer­ gers of 1924-25 (Food Research Institute Miscellan­ methods are as successful as getting to con­ eous P'ublication 3), January 1926. sumers bread that will be regarded by every­ 2 J. S. Davis and W. Eldred, Stale Bread Loss as a one as fresh. Problem of the Baking Industry (Food Research In­ In the United States, the problem was differ­ stitute Miscellaneous Publication 1), February 1923. ent. No wheat shortage was impending. The :J U.S. Food Administration, Release 450 (mimeo­ graphed), Nov. 11, 1917, p. 2. policy of the Food Administration was to re-

WHEA'r STUDIES, Vol. XII, No.6, February 1936 [ 221 ] 222 THE STALE-BREAD PROBLEM duce waste (and consumption) of wheat in However, American bakers were not unan­ order that the largest possible surplus above imous. Indeed, some of them have vigor­ domestic requirements might be available for ously fought all attempts of states and shipment to Europe. The Food Administra­ municipalities to prohibit the return of stale tion accordingly ruled against the return of bread to the baker. These bakers have felt unsold stale bread by retail distributors to that such measures would lead retailers to bakers and supplemented the regulation by force stale bread upon purchasers, and that publicity campaigns designed to enlist the aid this would cause the demand for bread to of bakers, dealers, and consumers in reducing fall and the volume of business done by the the waste of bread. Although the regulations baking trade to diminish. This has seemed were not universally enforced, they led to a especially important to American bakers great reduction in the amount of stale bread and millers because in the United States the returned. It has been claimed, however, that per capita consumption of flour has been de­ these wartime regulations were detrimental clining.2 to the small independent bakers because al­ These laws forbidding the return to the legedly they called into being numerous so­ baker of stale bread have had varying fates called "window" bakeries, exploiting the slo­ and caused not a little litigation. In some gan "Hot from the oven to you." states, they have been well enforced; in others, The bakers generally had found this state there has been more or less nullification. No of affairs so desirable that after the war, when recent study to determine the extent of the sharpened postwar competition threatened to losses and waste resulting from the return of bring back prewar wastes, they endeavored to stale loaves to bakers in the United States get laws passed in the several states-and seems to have been made. There is evidence, succeeded in some-continuing or re-estab­ however, that they have become greater than lishing the wartime prohibition of the return at the time of the Davis and Eldred estimate. of stale loaves to the baker. In some localities According to a survey made by Bakers Weekly food officials forbade the return of stale bread in the spring of 1930, the country-wide aver­ on the ground that it might be deleterious to age percentage of returns was 4.66. In indi­ health, since such returned bread is often vidual states, the average was as high as 7.5 handled carelessly, becomes moldy or con­ per cent. A year later, Pirrie expressed the taminated with filth, or is moistened and opinion that they had increased still more.S warmed to "freshen" it so that it can be sold to Murray has stated recently that losses from the consumer as new-baked. Partly because stale bread are often "as high as 5%, 6% or of legislation, partly because wartime prac­ even 7%."1 There are a number of reasons tices were adhered to voluntarily for a time, for this, which it would be well now to pass stale-bread losses were smaller than before in review. the war. In 1923, Davis and Eldredl esti­ In the days of the great baking mergers, mated the loss to the wholesale bakers of say in 1924-25, the wholesale bakers acquired the United States as probably averaging at production capacity which was not merely least 2.5 or 3 per cent of their sales. ample for that time but not infrequently de­ signed for an expansion which, taking the lOp. cit., p. 7. country as a whole, could not possibly come." "Holbrook Working, "The Decline in Per Capita Consumption of Flour in the United States," WHEAT On the contrary, the market of wholesale STUDIES, July 1926, II, 265-92; J. S. Davis, "The World bakers tended to contract with the growth of Wheat Situation, 1934-35. A Review of the Crop Year," chain grocery stores, which for the most part ibid., December 1935, XII, 176. a P. G. Pirrie, "House-to-House Stale Returns and have gradually come to produce nearly all Helations with Salesmen," Bakers Weekly, Oct. 10, their own bakery products. Many of the big 1931, LXXII, 47-48, 50. plants found themselves with overcapacity 4 C. Murray, "Manufacture and Distribution of and, indeed, the industry as a whole was-and Bread," Journal of Accountancy, March 1935, LIX, 190-200. still is-in this condition. Competition be­ G Alsberg, op. cit. came more severe not merely in the immedi- ECONOMIC AND SOCIAl.. CONSllJERATIONS ate vicinity of the large wholesalers, but held for the purpose of preparing a code, there these concerns, with improved bread-cooling was lively discussion of these proposed pro­ and -wrapping machinery and faster trucks, visions. It was obvious that the trade regarded and with better roads, also invaded the field the situation with reference to stale-bread of the rural retail and small wholesale baker. returns and consignment selling as serious. Naturally, their bread tended to be less fresh The outcome was a compromise. The return than that of the local baker and added its of stale bread was not prohibited, but the quota to the country's stale-bread loss. Fur­ ways in which such bread could be disposed thermore, bakers could, and did, deliver a of were prescribed. These ways were de­ great deal more bread than could be sold, for signed primarily to prevent unfair competi­ excess capacity made this possible with no tion between stale and fresh products and additional cost other than that for the in­ only incidentally to eliminate waste. "Con­ gredients, ilecause neither men nor machines signment" was defined to "mean the deliver­ were working at capacity. Moreover, ingredi­ ing, shipping, and/or placing of bakery prod­ ents were cheap. Many a baker succumbed ucts by a member of the Industry to or with to his desire to get a big display in each a retailer, wholesaler, restaurant or hotel grocery in the hope that customers might take keeper, or similar person, pursuant to an his bread. Striking differences existed between agreement or understanding that any prod­ bakers in the same region. ucts which are not sold will be taken back or Then came the depression. Many more per­ credit given therefor or price if paid returned sons than before sought to buy day-old bakery in whole or in part, or other allowance made." goods, because they were cheap. Many "stale" The national code did not prohibit these prac­ or "day-old" stores were opened in cities; and tices but made it permissible for any regional relief agencies bought day-old bread at re­ group of bakers to adopt a no-consignment duced prices. Some bakeries, in addition to provision if a truly representative group of their regular line, offered their day-old prod­ the bakers concerned demanded it. Such a ucts as a second grade in lieu of producing a demand was forthcoming in only a few re­ separate low-priced line. Eventually, it came gions. to serious competition between day-old and It is noteworthy that it did not seem to fresh bread. occur to anyone to define staleness. Stale There were, of course, other factors in addi­ bread under the code was merely bread re­ tion to the depression and intensified compe­ turned to the bakers unsold. No time limit tition due to over-capacity. One of these was was established on the age of bread after the now well-nigh universal practice of selling which it was to be regarded as stale. This bread ready sliced as well as wrapped. It was probably because the trade as a whole is less easy for the purchaser at retail to tell is unacquainted with the existence of any ob­ the condition of the loaf by the feel. Also jective test by which staleness may be estab­ bread in this form is said to grow stale faster lished. It is clear that it is extremely difficult than when unsliced. to enforce any law or regulation unless stale­ These changes in the baking industry ness is defined either in terms of the age of caused a realignment of the several classes

of producers. It had always been recognized 1 Wholesale bakers who sell to retailers rather than that consignment seIling1 was at the bottom house-to-house do so through the drivers of their de­ of the stale-bread-loss difficulties of the trade; livery wagons. These employees are both salesmen and drivers. They determine to a large extent how but it seemed hopeless to expect help from many loaves to leave in the shop of each retailer. officials and legislatures in meeting the situa­ Since they are usually paid in part on a commission tion. The National Industrial Recovery Act basis, they are under the temptation to stock the re­ tailer with too many rather than too few loaves. The created this possibility. It seemed feasible to retailer tends to be indifferent, for he does not pay for enact a code for the trade which would deal the fresh bread. On his next visit, the driver takes efTectively with the return of unsold bread and away the stale loaves and collects payment only for those that have been sold since his preceding visit. with consignment selling. At the hearings This is consignment selling. 224 THE STALE-BREAD PROBLEM bread or in terms of some objective chemical or signment selling were abolished, retail grocers physical test. To attempt to define staleness in would force stale bread on customers as fresh. terms of the age of the bread is not at present This, it was believed, would injure the reputa­ feasible, for the onset of staleness depends tion of the brand that happened to be sold in upon the character of the loaf, the methods this way and cause demand. for it to slacken. of production, and the conditions to which it It would seem that, despite the weakness of is subjected after it leaves the oven. If the the Bakers' Code with respect to stale-bread industry desires to cope with its stale-bread returns and consignment selling, it had some problems through governmental processes effect in reducing wastes. After it became in­ which must stand the test of court review, it operative when the Supreme Court held the seems obvious that objective physical or chem­ National Industrial Recovery Act to be un­ ical tests for the determination of staleness constitutional, only regional codes promul­ are essential. What progress has been made gated. under state acts remained in force. in meeting this problem is set forth in this Certain it is, therefore, that the growing stale study. of baked products is still a question of impor­ The hearings on the code showed that the tance, not merely to bakers but also to con­ position of bakers was in effect as follows: sumers, for undoubtedly the losses to bakers Many retail bakers favored prohibition of are passed on to consumers in the form of consignment selling, because they believed higher prices. many retail outlets in their own neighborhood An important social question is also in­ would cease to carry the wholesalers' product, volved-night work by bakery employees to bread possibly excepted, if the owner had to satisfy the insistent demand of the consuming gamble on the sale of bread and cakes. In public for very fresh bread. In some countries cities, they tend to be more concerned about more advanced in social legislation than the cake and pie than about bread on which the United States, this is a serious question. In profit tends to be smaller. Holland, for example, night work by bakers Rural wholesalers also opposed consign­ is in violation of law and the sale of bread ment selling. They believed that the great so fresh that it can be produced only by such wholesale bakeries in the cities would not work is prohibited. In consequence, as we then sell so readily to rural outlets far away, shall see, special techniques to prolong the because rural grocers would not take the risk life of bread have been developed there. Un­ involved and would prefer to stock a small fortunately, they have not yet been put into supply from the local wholesale baker and general practice. It would undoubtedly be a replenish it later in the day if necessary. social gain for the United States if ways and The great wholesale bakers were divided. means, adapted to American circumstances, At heart few of them favored consignment could be found to do away with night work. selling, but they could not forecast what might Large-scale production of bread is growing. happen. They knew they could not afford to This tendency increases the importance of take chances; even a small loss of business the stale-bread-Ioss problem in two ways. Di­ would be serious. Some thought that the rectly, it enlarges the field within which con­ grocer would tend. to stock only one or two siderable losses from stale bread are to be brands of bread, and they did not know expected. Indirectly, a general reduction in whether it would be their bread or that of the loss from this source, like other economies someone else. Others feared that if the grocer in production or distribution, will tend to were forced to risk his own capital on his permit the baker to sell on a narrower mar­ bread sales the various grocers' organizations gin and thus to extend the market for his might establish their own bread plants, on the products into homes where household baking theory that, if they must gamble individually, is practiced on grounds of economy. they might as well gamble in a group and The situation can be improved in three spread the risk. Finally, as above pointed out, ways: by better adjustment of production to many wholesale bakers feared that, if con- demand, by better distribution, and by pro- STRUCTURE AND BEHAVIOR OF STARCH GRAINS 225 longing the life of the loaf. With the first and, although the purpose of the writer is two of these, this study is not concerned. It to treat it in a nontechnical manner, some deals primarily with the aging of bread. Pro­ readers may prefer to turn at once to later longing the life of bread is one of the most sections which have been written, it is hoped, important of the practical problems that con­ so that they can be understood by themselves. front scientists engaged upon the improve­ The starch granules of wheat are discrete ment of the technique of food manufacture. particles of microscopic size and more or less The shortness of the life of bread sets limits of the shape of disks or bilaterally flattened to the size of bread factories because their spheres or saucer-shaped. They exhibit a se­ market is restricted to the territory in the ries of rather faint concentric rings-probably vicinity which can be reached in not too long because they are built up of a series of layers; a time. Longer routes are attempted in the in other words, they have a laminated struc­ central part of the country than in the At­ ture. When a beam of light is passed through lantic or Pacific states. More speedy transpor­ them, they change its direction and break it up tation or prolonged life of the loaf or both into two components. This property is termed would make larger bread factories and more "double refraction" or "birefringence." Starch effective mass production possible with the grains are doubly refractive or birefringent. economies of production and distribution Birefringence can be made manifest to the eye therein involved. if polarized light is passed through the gran­ As in medical research a specific for a ules, i.e., light consisting solely of waves disease is rarely found until the cause behind which vibrate in the same plane. The polar­ the disease-its etiology-is fully known, so izing microscope is an instrument which per­ other scientific problems are rarely solved mits only such polarized light to pass through until the phenomena involved are fully under­ the object under examination. Starch grains stood. We can hardly hope, except as the viewed through such an instrument manifest result of a lucky accident, to learn how to their birefringence by showing a so-called prevent or even appreciably to delay the grow­ black cross. The granules exhibit alternate ing stale of bread until we fully understand luminous and dark quadrants so arranged what this process of growing stale really is. that the dark areas appear like a more or less Much progress has been made in recent years regular black cross. in its investigation. It is our purpose here to Many crystals are birefringent, but non­ bring this material together, and to examine crystalline materials may also exhibit this it critically in the hope that further research property when they are subjected to a me­ will be stimulated thereby and that the prac­ chanical stress or strain. A sheet of well­ tical application of what is already known annealed glass, for ex~mple, may exhibit will be furthered. birefringence when it is put under stress by bending. Substances which are built up in STRUCTUHE AND BEHAVIOR OF STAHCH GRAINS! such a way that their component parts are The aim of this section is to describe those arranged in some orderly fashion, for example properties of starch which are involved in the if the components are all placed parallel like aging of bread, for, as we shall see, these corded firewood, may also exhibit birefring­ properties are important factors-perhaps the ence. most important ones-in the growing stale of Starch grains in their natural state are crys­ bread. Acquaintance with the properties of talline, at least in part. By crystalline, we mean starch should render it easier to grasp the that the molecules are arranged in some or­ phenomena concerned in the aging of bread. derly fashion. This does not necessarily imply Unfortunately, the subject is complicated, that the granule or its components possess a geometric form such as we are accustomed to 1 Cf. C. L. Alsberg, "Studies upon Starch," Indlls­ find in an ordinary crystal, say rock candy. trial and Engineering Chemistry, February 1926, ~VnI, 190; and "Starch and Flour Quality," WHEAT Many botanists have claimed that starch gran­ STUDIES, Febl'Uary 1935, XI, 229-54. ules are of crystalline structure, but final 226 THE STALE-BREAD PROBLEM

proof became possible only in recent years When starch granules are heated with through the use of the X-ray. water, their X-ray diagram or pattern under­ Parallel X-rays falling upon a photographic goes changes. In the case of wheat starch, the plate after passage through a crystalline sub­ change in this pattern depends upon the stance produce a pattern which appears when amount of water present and the temperature. the plate is developed. 'Illis pattern is known Katz has named the X-ray pattern of natural as an X-ray spectrum or X-ray diagram. It is unaltered wheat starch its A-pattern.2 If such characteristic of crystalline structures. The starch showing the A-pattern be heated to X-ray thus permits us to determine whether 100° C. with but 50 per cent of its weight of a substance which presents no evidence of water or if it is heated with an excess of water crystallinity to the eye is in fact composed to only 60° to 70° C., its A-pattern is trans­ of crystals too minute to be visible or has an formed into a new pattern, which Katz has orderly arrangement of its molecules. It is termed the V-pattern. The starch apparently unnecessary for present purposes to explain has been converted from one crystalline state why this is so or what conditions must be to another. Katz3 has named this state of observed in performing such experiments.1 starch first-degree gelatinization. What concerns us here is that starch gran­ A starch granule in the state of first-degree ules in their natural state behave in this way. gelatinization is somewhat swelled, and in They must therefore be crystalline. It is the larger ones this swelling may have caused highly probable that they consist of tiny hair­ the center of the granule to become converted like crystals which the older botanists called into the beginnings of a cavity which is some­ trichites, from the Greek thrix, a hair. These times irregularly star shaped. The granules are probably arranged radially, i.e., one end have become more permeable, for they stain is directed toward the interior of the starch with such dyes as Congo red and, when placed granule, the other toward its periphery. The in water, they permit some of their substance trichites thus lie more or less perfectly to diffuse out. Natural, uninjured, unheated parallel. granules, on the contrary, neither stain with these dyes nor are they soluble. It is not to be inferred that the greater solubility of gelat­ 1 The reader who is interested in pursuing this sub­ ject further is referred to the standard texts, for ex­ inized starch is due necessarily to chemical ample: G. L. Clark, Applied X-Rays (New York, Mc­ change of the starch substance, for mere me­ Graw-Hill,1927). chanical injury, such as cracking, renders 2.J. H. Katz, "X-Hay Investigation of Gelatinization and Hetrogradation of Starch in Its Importance for starch soluble to an appreciable degree in Bread Hesearch," Bakers Weekly, Mar. 24, 1934, LXXXI, cold water.4 34-37, 46. The results of the X-ray studies of Katz and If wheat starch in first-degree gelatinization of his co-workers have been recorded in a series of papers in Zeitscllrift filr phllsikalische Chemie, Ab­ is held at a temperature below 60° to 70° C. for teilung A. some time, it changes. According to Katz," 3.J. R. Katz, Ret Oudbakken Worden van het Brood it becomes less translucent, there is less sol­ in Verband met het Vraagstuk van den Nachlarbeid uble starch in it, and its X-ray V-pattern der Bakkers (Dissertation, Amsterdam, 1917; 's-Gra­ venhage, van Langenhuysen, 1917), Part 1, p. 17. This changes to a new one, the B-paUern. Its crys­ dissertation has been published in German and some­ talline form has again changed and this what modified in a series of articles appearing in change proceeds more rapidly at lower tem­ Zeitschrift filr das gesamte Getreide- Milhlen- lind Biic/cereiwesen. peratures. The rate of change becomes maxi­ 4 Alsberg, "St.udies upon Starch. mum at _2° to _3° C.6 At stilI lower tem­ r, "X-Ray Investigation of Gelatinization and Hetro­ peratures, it is slowed up again, until at quite gradation of Starch in Its Importance for Bread He­ low temperatures, for example that of liquid search"; Ret Oudbakken Worden van lIet Brood in Verband met het Vraagsiuk van den Naclltarbeid der air, it does not occur at all. Balckers. If wheat starch in the state exhibiting this 6 It may be that free water is required for the B-paUern is warmed up to over 60° to 70° C., change. At low temperatures, the free water present in the granule, having been converted into ice, may no it is converted back again into starch exhibit­ longer be able to playa role in the conversion. ing the V-pattern. Allowed to age at lower STRUCTURE AND BEHA VIOR OF STARCH GRAINS 227

temperatures, it turns back again into the B­ boiled, aqueous suspension, also undergoes pattern form, and it may thus be changed gross changes visible to the naked eye. Paste, hack and forth from one form to the other, more or less translucent when newly made, provided care is taken to prevent too great a gradually turns opaque and white. Thin sus­ loss of moisture. pensions gradually cloud up and ultimately If, instead of heating with insufficient water separate a sediment. The supernatant liquid Of at a low temperature, the granules are may become nearly clear and ultimately con­ heated to 1000 C. with an excess of water, the tains starch in accordance with its solubility method of making paste, the X-ray pattern in water.3 Paste, if not too concentrated, may disappears altogether; the starch has changed also separate into a solid and a more or less from the crystalline to the noncrystalline or liquid portion. amorphous state. This state Katz has termed Wheat starch which has aged in this way second-degree gelatinization. seems to differ from natural wheat starch The starch granule in this state is greatly in that it is very difficult to disperse it again swelled. The individual granules have the by heating in water. Gelatinized starches ex­ appearance of hollow elastic bags filled with amined by the writer (potato, maize, wheat) liquid. Some of the starch substance has did not again regenerate the paste when re­ diffused out into the surrounding water. The heated. The reasons for this are probably in granules stain easily and there is, of course, part merely mechanical. A starch paste owes no sign of birefringence. The black cross its consistency to its structure visible with has disappeared. the ordinary powers of the microscope.4 In it, Starch in second-degree gelatinization also the swollen granules occupy nearly all the changes with time. It returns again to the volume of the system, so that they touch and crystalline form and like first-degree gelatin­ compress one another. Thus the system ac­ ized starch ultimately shows an X-ray B-pat­ quires firmness. Anything that breaks up this tern. This change is accelerated or retarded structure through breaking up the individual by lower temperatures, much as in first-degree granules so that they collapse converts starch gelatinization. The change in pattern is more paste into a syrup, because the swollen gran­ rapid in the presence of much water than of ules no longer touch and support one another. little,! and different starches change at differ­ This is the effect of grinding in a pebble mill,G ent rates, other things being equal. Potato or of freezing. Such a syrup is very cloudy starch changes more rapidly than starches and stilI contains in suspension bits of paste from the seeds of cereals. Whether this is true and uncollapsed gelatinized granules that have of seed starches in general does not seem to escaped attrition. It cannot again be converted have been investigated.2 into paste by heating. Its starch, unless the Starch in second-degree gelatinization, as syrup has aged, is still amorphous, but some when it is in the form of paste or of a thin, of it becomes crystalline in time. As above stated, once it has taken this insoluble form, 1 Katz, "X-Hay Investigation of Gelatinization and starch is very difficult to disperse in water Hctrograliation of Starch in Its Importance for Bread Hesearch." again by merely boiling. It is no longer like 2 Ibid. the natural starch from which it was formed " .J. Field II, "Specific Hotation and Phosphate Con­ -why is not well understood. lent of Cold-Water-Soluble Fractions of Ground Corn and Wheat Starches," Proceedings of the Society for Starch granules consist of at least two sub­ Experimental Biology and Medicine May 1928 XXV stances, a-amylose, which is very insoluble, 711-12. " , and ~-amylose, which is somewhat soluble in 'J Alsberg, "Studies upon Starch," water. How these two carbohydrates are laid , t. C, L. AIsberg and E. E. Perry, "The Effect of Grind­ J~lg ,uJlon Starch and Starch Pastes," Proceedings of the down in the natural granule with respect to S()(,lely for Experimental Biology and Medicine, Octo­ one another is not known. It is not even ber 1924, XXII, 60-61. known whether they are both crystalline or "K. H. Meyer, H. Hopff and H. Mark, "Ein Beitrag zur Konstitution der Starke," Berichte der Deutschen only one of them. According to Meyer, Hopff chemischen GesellscIzaft, May 1, 1929, LXII, 1103-12. and Mark,o a-amylose (amylopectin) is crys- 228 THE STALE-BREAD PROBLEM talline, but ~-amylose is amorphous. But, ac­ volved a simple physico-chemical equilibrium cording to van Hallie,l both have a V-pattern reaction.4 In 1917, he even went so far as to if prepared from fresh wheat-starch paste, but suggest that probably this reaction involved a B-pattern if prepared from aged paste. the taking up of water, the break-up of the Raw starch granules, if ground up and me­ starch molecule, and the opening up of a chanically injured, give up f3-amylose to cold union of two hydroxyl groups, one of which is water, and if enough of it be used practically presumably an aldehyde and the other a hy­ all the ~-amylose may be extracted from droxyl group. To, the freeing of hydroxyl raw, finely ground starch. However, the solu­ groups in this manner, he attributed the tions so obtained are opalescent; in time most greater water-binding power of gelatinized of the ~-amylose flocculates out, and ulti­ starch. Gelatinization he believed to be a matelya clear liquid may be obtained by filtra­ chemical reaction which involves the taking tion which hardly shows the Tyndall effect up of water. This view is not tenable, because, and which contains from 0.1 to 0.5 per cent as has long been known, merely injuring a of ~-amylose.2 In other words, one obtains starch granule causes it to swell in water at the colloid equivalent of a supersaturated the site of injury and permits some of its sub­ solution which ultimately separates out a stance to disperse into the surrounding solu­ merely saturated solution. tion. G It is therefore indubitable that the Indeed, from boiled starch, all the ~-amylose swelling power of starch granules may be may easily be extracted, and this has been modified by procedures which cannot possibly proposed by Biedermann3 as a method for involve a chemical reaction within the com­ its preparation. This is what happens in the mon meaning of that term. analysis of bread crumb and the amount of After Katz had made his X-ray stUdies, he soluble starch obtained depends upon the modified his position in that he then assumed conditions of extraction. As time goes on, that aging involves a heterogeneous reaction. the change in swollen granules above de­ He insists, however, that we have to deal with scribed makes it more and more difficult to a physico-chemical equilibrium, as he main­ extract ~-amylose. tained in his earlier publication. His evidence Katz, in his earlier pUblications before he is that the transition of starch from one form had discovered the changes in X-ray patterns to the other, as determined by swelling power that occur in gelatinization, expressed the and amount of soluble amylose, depends upon view that the aging of gelatinized starch in- the temperature and yields a continuous curve with a narrow temperature interval.° It may 1 T. B. van Hallie, Bijdrage lal de Kennis der Ver­ well turn out that this view is correct, but in slijfseling en Relroaaradalie van Zelmeel door Middel the present state of our knowledge it really van de Ronlaenspectra(fraphie (Dissertation, Amster­ dam, 19:10; Amsterdam, D. B. Centen's Uitgeversmij. means very little. As Bayliss puts it: " .... the IN.V.],1930). temperature coefficient of a process cannot 2 Field, op. cit. be used to decide whether it is chemical or " \V. Biedermann, "Starke, Stiirkekorner und Stiil'ke­ physical. That of some physical processes is !Osungen," Pfluger's Arclliv fur die aesamle PI1/lsi­ olollie des Menschen und der Tiere, 1920, CLXXXIII, practically identical with that of certain other 1 (j8-9 (i. chemical reactions." And again when discuss­ 1.J. H. Katz, "Die Ursachen des Althackenwerden des ing enzyme reactions: "When a simple hetero­ BI'otes vom physikalisch-chemischen Standpunkt be­ tl'achtet," Zeilschri[l fur Elektrocl1emi-e, Feb. 15, 191:l, geneous reaction, such as that of dissolving a XIX, 202-06., piece of zinc in sulphuric acid, takes place, its r, Alsberg, "Studies upon Starch." rate depends on how fast the acid molecules IJ.J. R. Katz and L. M. Rientsma, "Abhandlungen zur diffuse to the zinc, and how fast the zinc sul­ physikalischen Chemic del' Starke llnd del' Brotbe­ reitung. II. Die Starke-Modifikation mit V-Spektrum phate difl'uses away. But when the solid phase (Vel'ldeisterllngsspektrum) ist bei hoherer Tempera­ is in the form of colloidal particles in constant tUI' die Gleichgewichtsfol'm, bei niedrigel' Temperatur Brownian movement, as in enzymes, diffusion ist es die Modifikation mit B-SpektI'llm (Retl'ograda­ tionsspeldrum )," Zeiischri[l [iir pl1/lsikaliscl1e Chemie, plays a negligible part, because the agent is Abteilung A, September 1930, CL, 60-66. uniformly present, and the distance which the STRUCTURE AND BEHAVIOR OF STARCH GRAINS 229 substrate molecules have to travel is very sible for the pattern. Katz and Rientsma put short. Here the rate of reaction is controlled it thus: The assumption, for example, that by that of the chemical reaction itself. The the V-spectrum is merely the consequence of fact that an enzyme reaction may follow a the development of irregularity in the crystal unimolecular law, or that it has the tempera­ lattice is adequately disproved by the fact that true coefficient of a chemical reaction, throws higher temperatures would maintain just this no light of significance in the mechanism of disorder of the lattice. The facts would only the process as a whole."! The setting and then be understandable by means of an auxil­ melting of a gelatin or agar gel is, so far as iary hypothesis to the effect that this irregu­ chemical behavior is concerned, no different larity of the lattice is the consequence of con­ from that of gelatinized starch. For a given version into another modification.' set of conditions, each melts and sets at the However, treatments which cannot con­ same temperature, and a solid gelatin gel in ceivably cause chemical changes in the starch time may even separate out dense bodies sug­ substance do affect the X-ray pattern. Thus gestive of spheroliths-indeed, Bradford con­ mere mechanical injury deprives starch of siders them crystalline. its power to exhibit an X-ray spectrum." Fur­ More recently, Katz and Derksen have modi­ thermore the X-ray pattern of natural starch fied the views of Katz still further to explain seems to depend upon the presence of some why it is that granules of different size gela­ moisture. Anhydrous starch does not give an tinize at different temperatures. They assume X-ray spectrum.6 It again shows such a spec­ a structural factor in the granule (gewachsene trum when moistened. Therefore the change Slrukiur). They suggest that the behavior of of starch during gelatinization from one form the individual granule is determined by one giving a certain X-ray pattern to another giv­ variable more than by the ordinary physico­ ing a different pattern need not necessarily chemical phase.2 This structural factor may be the result of such a chemical change, as merely be the expression of differences in in­ Katz suggests. We may have to do merely ternal pressure developed as a result of differ­ with changes in water of hydration or water ences in granule size. 3 of crystallization. The different forms of Moreover, as above indicated, there are wheat starch conceivably may be merely the other possible explanations for the X-ray spec­ same starch associated with difTerent amounts trum changes described by Katz besides the of water. one he adopted, to say nothing of one con­ Another interpretation also suggests itself. sidered and rejected by him, namely, deforma­ We know that starch consists of more than tion of the lattice structure which is respon- one substance. We know that these have dif­ ferent solubilities. They must therefore dis­

1 W. M. Bayliss, The Colloidal Slale in lls Medical perse at difTerent rates when warmed with and Physiological Aspecls (London, Frowde and Hod­ water. It is conceivable that in natural native der & Stoughton, 1923), pp. 58, 79. starch granules we get a composite X-ray 2,J. n. Katz and J. C. Derksen, "Abhandlungen zur physikalischen Chemie del' Starke und del' Brot­ spectrum of more than one substance, and hcreitung. XVI. Wiedervcrkleistcnmg des l'etrograd­ that at higher temperatures the spectrum is iCl'ten Stiil'l

enough evidence inconsistent with it to give Lhe introduction of the idea that starch as a one pause. colloid behaves differently from other colloids Maquenne applied the term "retrograda­ was unfortunate and has caused confusion tion" to the behavior of gelatinized starch that is only now being cleared away. whereby it becomes less translucent and may The separation of liquid in the process of separate under suitable circumstances into a retrogradation is probably a special case of precipitate and a liquid. He, Roux, and other syneresis. Syneresis is the well-known phe­ French investigators regarded this phenome­ nomenon that many gels or jellies in time non as peculiar to starch and published many "weep" or sweat out fluid, as for examplc the papers upon it. Their observations, however, separation of serum from a blood clot, the were by no means new. Many of them had separation of whey from milk clotted by ren­ been made as long ago as 1840 by Jacquelin.! net, or the formation of "condensation water," Maquenne believed that the solid material so-called, in a gelatin or agar bacterial culture. separated in retrogradation was identical This elimination of solution from the jelly chemically with natural starch, and he de­ is probably secondary to changes that take scribed "artificial" starch granules in it, i.e., place in the finer physical structure of starch bodies that looked like very small natural gel. We now turn to consideration of this starch grains. He termed the process "retro­ structure. gradation" because he thought the starch had The coarser structure of starch paste which stepped back, retrograded, from the form in is visible with the ordinary powers of the which it is found in solution or in paste into microscope has been described above. But its original condition in the native granule there is also a finer submicroscopic structure before it was dispersed in water or converted which is not thus visible and is not at all well into paste. In the case of wheat starch, at understood. The natural granule consists, as least, Maquenne was wrong, for, as above we have seen, of fine crystalline trichites and pointed out, Katz has shown that the X-ray these in turn consist of bundles of long chains pattern of retrograded wheat starch is not the of atoms.4 In gelatinization, these chains are same as that of natural starch.2 As we have probably disarranged, so that they lie every seen, there are other differences also between which way instead of parallel as they do in the retrograded and natural starch. Retrograded unaltered granule. Perhaps, too, they become starch is not so easy to disperse as natural more or less broken into shorter pieces. A starch, and it is more resistant to attack by "brush-heap" structure is what one would diastase, the enzyme of malt. expect to result. This structure might he Today the idea of retrogradation seems likened to cord wood piled haphazard. In this quite unnecessary;3 all its phenomena may be form, it occupies a larger volume and the explained in harmony with the behavior either aggregate volume of the spaces between Lhe of supersaturated solutions or of gels. Indeed, sticks is far greater than when the same wood is neatly stacked with all sticks tightly pacl

and pack themselves in some orderly fashion. one need not accelerate the other. Thus Katz One of the ways for them to do this is to states that starch in first-degree gelatiniza­ erystallize, for in a crystal the packing of tion changes from its X-ray V-pattern to its the atoms is the closest possible. In the proc­ retrogradation B-pattern in much less time esS, the submicroscopic interstices of the than it takes second-degree gelatinized starch, hrush-heap structure must, of course, become which has no characteristic X-ray pattern be­ fewer and larger. cause it is not crystalline, to acquire the B­ If there is a relatively great amount of pattern of retrograded starch.4 Indeed, there liquid as compared with the mass of the crys­ is no evidence that first-degree gelatinized tallizing substance, the interstices become too starch separates out liquid, that is to say, large to retain the liquid mechanically; it synerizes. The experiments of Meyer" indi­ leaks or sweats out and the mass of the gel cate that liquid is not extruded. He found may shrink: the gel synerizes. If the mass of that a gel made by heating 5 per cent of arrow­ crystallizing substance is relatively great and root starch in water to 138 0 C. and held at the volume of liquid relatively small, all the +20 C. for 12 days was white, brittle, compar­ liquid may still be retained-at least for a atively firm, and had not extruded fluid ([{on­ very long time, and syneresis does not occur.! dens wasser ). More concentrated gels reach Hence dilute gels, other things being equal, this condition in a shorter time. They are synerize soon, while very concentrated gels transparent at first and then become opaque, may synerize very slowly or not at all within and if they have been heated only to the tem­ finite time. 2 Indeed the structure of dilute gels perature of bread in the oven, viz., 100 0 C. or is ordinarily fundamentally different from less, instead of to 1380 C., the temperature that of concentrated gels.s Meyer used, their tendency to synerize is less It follows that in the aging of such a gel as the more concentrated they are. starch paste two phenomena occur which in­ Though anticipating some of what is to vestigators who have written of retrograda­ follow, we may now in this summarizing tion have not always distinguished. One is paragraph review those starch properties the primary phenomenon, recrystallization or which appear to play a part in the aging of its equivalent; the other is the secondary bread: Starch gelatinized with little water phenomenon, syneresis, which, as we have swells somewhat by imbibing water and seen, mayor may not occur within finite time. changes its crystalline nature in a manner The two phenomena need not proceed at the demonstrable with the X-ray. This state Katz same rate and conditions which accelerate has named first-degree gelatinization. Starch in this state changes its crystalline form as it 1 The writer does not mean to be understood as ages, again demonstrable with the X-ray. So taking the position that all gels have a long-chain structure or that all syneresis is due to crystallization. far as its X-ray pattern is concerned, wheat On the contrary, some gels show quite different condi­ starch retrograded in this way may be con­ tions and also synerizc. Indeed, fundamentally, the verted again to its condition before retrograda­ separation of an emulsion into its component liquids seems to the writer, in essence, the analogue of syne­ tion by heating. Again aged, it retrogrades resis. again and can be rejuvenated again. So long 2 W. B. Hardy, "Ober den Mechanismus der Erstar­ as loss of moisture is prevented, the process nlllg in umkehrharen Kolloidsystemen," Zeitscl1rift may be repeated back and forth many times. fiir pl1l1si/wlisc11C Cl1emie, May 2, 1900, XXXIII, 326- 4:1; S. Woodruff and L. R. Webber, "A Photomie.)·o­ There is no evidence that water is set free graphic Study of Gelatinized Wheat Starch," .Tournal in retrogradation of first-degree gelatinized ()f Arlriculiural Researcl1, .June 15, 19:13, XLVI, 1099<- 1108. starch. It is otherwise with second-degree n Hardy, op. cit. gelatinized starch, which is starch heated with 1 "X-Ray Investigation of Gelatinization and Retro­ excess of water. Such starch, if in the form of gradation of Starch in Its Importance fOI' Bread Re­ not too concentrated a paste, separates water search." irreversibly as it retrogrades. Many kinds of "A. Meyer, "Beitriige Zllr Kenntnis del' GalIel'tcn, hesonders der Stiirkegullcrten," [(olloidcl1emiscl1e Bei­ reasonably dilute gels exhibit this phenome­ hefte, Aug. 2:1, 1913, V, 1-48. non, which mayor may not be irreversible. 2:32 THE STALE-RREAD PROBLEM

It is known as syneresis. It is secondary to quired their full strength and become old and retrogradation, i.e., it is the consequence of clear. It was rather a term of quality and change in the state of the starch, but not a came to be applied to something altered by necessary one, for very concentrated gels do keeping, "but when said of bread it is the not synerize, at least they do so extremely ordinary opposite of new, without necessarily slowly. Hence, a very concentrated starch gel, implying inferiority."i as in first-degree gelatinization, synerizes very Staleness in bread is the change in flavor slowly, if at all, though it may retrograde very and texture that develops in time. What is rapidly. Its behavior is quite different from called flavor is really the resultant of a num­ that of second-degree retrograded starch in­ ber of factors. It is not simply a matter of vestigated by Maquenne, Roux, and others. the reaction of the taste buds, on the back and Retrogradation is affected by temperature. sides of the tongue and in the throat, to a Wheat starch in first-degree gelatinization specific stimulus. Flavor involves not merely does not retrograde at a temperature above the sense of taste but the sense of smell as 60° to 70° C., but retrogrades with increasing well. Closing the nose by pinching the nostrils velocity as the temperature is lowered below eliminates smell and only taste remains. Un­ this range. The velocity passes through a der such circumstances or when one has a maximum at _2° to _3° C. As the tempera­ cold in the head, one is reduced to a state ture is lowered further the rate of retrograda­ in which food seems to be without flavor, for tion slows up until at quite low temperature only sour, saline, sweet, and bitter tastes retrogradation ceases altogether. can be sensed, and onions produce the same sweetish taste that apples do. 2 The sense of MANIFESTATIONS OF STALENESS smell is incredibly delicate; the sense of taste, The word "stale" was probably derived comparatively crude. Since bread is not from the root of the Teutonic word meaning markedly sour, salty, sweet, or bitter, no "to stand," and was applied to fermented doubt a considerable part of its flavor is due beverages that had stood till they had ac- to its effect upon smell. Upon just what sub­ stances the odor of fresh bread depends and ] A New EnglisIl Dictionary . ..., edited by .J. A. H. what changes they undergo as staleness de­ Murray, et al. (Oxford, Clarendon Press, 1919), Vol. velops is quite unknown. Possibly alcohol IX, Part 1, p. 782. and other volatile substances" produced by the 2 G. H. Parker, Smell, Taste, and Allied Senses in tIle Vertebrates (Philadelphia, Lippincott, 1922), pp. yeast fermentation are involved, for fresh 173-74. bread, despite the heating to which it was "HecentIy Visser t'Hooft and de Leuw have found subjected in the oven, still contains small acetylmethylcarbinol, CH" . CO • HCOH . CH, (syno­ amounts of alcohol. If, indeed, flavor is de­ nyms: methylacetol, dimethylketol, and dimethylgly­ colose), in ripe dough and bread. This substance was pendent upon volatile substances of this sort, first identified by C. A. Brown in abnormal cider vin­ one would expect that, when stale bread is egar and by Pastureau in abnormal wine vinegar. It freshened by warming in the oven, the flavor was identified as a constituent of all cider vinegar by H. W. Balcom ("The Volatile Heducing Substance in would be improved through the vaporization Cider Vinegar," Journal of tIle American CIlemical of the flavoring substances-as indeed it is. Society, February 1917, XXXIX, iJ09-15). C. B. van Niel, A. J. Kluyver and H. G. Dcrx ("Ober das In this connection, it is significant that Butteraroma," Biocllemisclle Zei/scIlrift, 1929, CCX, many bakers believe bread prepared from 2:J4-51) found it and its oxydation product, diacetyl, dough that has been subjected to fermentation CH" . CO . CO • CH" in butter and attributed to it a role in butter flavor. Acetylmethylcarbinol itself has for a long time tends to grow stale more slowly no aroma, but diacetyl has. The role the formel' plays than bread made from rapidly fermented in bread is as yet uncertain. According to K. Farn­ dough. Whether this view is justifiable does steiner (Z. NaIlr.-Genussm., II, 198-209 [1899]; cited not seem to have been determined by exact by Balcom, op. cit.), it is not present in cider or wine but develops in them as they undergo acetous fermen­ measurements. If it is, it may be that one of tation. It is possible, therefore, that it is not formed the factors involved is flavor. One would ex­ in dough by yeast, but by accompanying micro-or­ ganisms, as it is, according to van Niel, Kluyver and pect bread made from a long-fermented dough Derx, in the souring of cream. to contain more alcohol, more volatile acids, MANIFESTATIONS OF STALENESS 233

and more of the other volatile products of fer­ containing starch, if it has to he chewed long, mentation than short-fermentation bread. tends to become sweetish. These suhstances would therefore tend to dis­ In short, one may speculate about the na­ appear from such hread more slowly than if ture of the processes that cause the flavor of less of them were present and, in so far as bread to change as it grows stale, hut there is hread flavor depends upon them, one would as yet no adequate body of facts on which to expect long-fermentation-time bread to re­ build even a hypothesis regarding the proc­ tain the flavor of freshness for a longer period esses involved. The changes themselves are than short-fermentation-time bread. How­ known to everyone. They are quite different ever, this is at present a mere speculation; in the crust and the crumh. experiments to test its validity still remain to The crust, if it is slightly hitterish, due to be made. caramelization of starch in the oven's heat, Sourness is also a factor in the flavor of remains so. The dry, crisp texture of the bread. A long fermentation time tends to pro­ crust of fresh bread contributes to the judg­ duce more acid bread. Perhaps a considerable ment that the bread is fresh, just as the pli­ degree of acidity masks the characteristic able, soft, and leathery crust of stale bread flavor of bread to some extent and therehy contributes to the opposite judgment. But renders change of flavor with time less notice­ texture or feel in the mouth is a sensation able; possibly, acidity in hread directly affects which many persons do not distinguish from its flavor. Tryller,' in his study of adsorption flavor. Moreover, as above suggested, a crisp by starch granules, has reported that the po­ crust tends to be chewed longer, to cause a tassium and sodium compounds of potato more copious flow of saliva, and this in turn starch possess a flavor reminding one of tends to give a sweetish taste. The change in wheaten flour. The calcium compound has a flavor of the crumb is more marked than that slightly chalky flavor. It is conceivable, there­ of the crust, but, as we have seen, the reasons fore, that if there is much acid in bread this are not understood at all. No doubt, the hard­ acid may gradually remove some of the potas­ ness and toughness of the crumb demand sium and sodium from its combination with longer and more thorough mastication, but the starch of bread and so in time in some de­ the change in flavor is pronounced before this gree affect the bread's flavor. It is not impos­ factor would seem to be of much importance. sible also, if Tryller's observations are cor­ The change in texture of the crust is an rect, that the hardness of the water used in easily understood phenomenon. In the oven, doughing may be a factor in flavor. Certainly the crust is desiccated much more than the it is well known that the character of water crumb and thereby acquires greater power to is important in determining the flavor of attract moisture. Therefore, as the loaf grows malt beverages. old, the crust attracts moisture from the in­ Texture may also affect flavor indirectly. terior until it is in equilibrium with the Everyone knows, as bread grows old, that the crumb. As it aproaches this state, it becomes crumb becomes harder and tougher, more softer, less brittle, and more or less leathery. crumbly, and in the course of time hard and The changes in texture of the crumb are brittle. Old and fresh bread chew differently. more complex. They are not due to drying Ordinarily dry foods are chewed longer and out. 'Vith advancing age, the crumb of course through their dryness stimulate the flow of dries out ultimately, but bread becomes stale saliva. Dry bread causes an abundant flow. long before it has lost an appreciable part of In saliva, there is a chemical agent, the en­ its water. The change in texture of crumb zyme ptyalin or salivary amylase, which con­ really takes place in three stages: first it be­ verts the starch to maltose or malt sugar. This comes tougher and harder, next it becomes sligar is sweet and so the navor of a foodstuff crumbly, and finally after a much longer time it dries out. 1 H. Tryllcr, "Beitriige zur Chemie del' Kartoffel­ stiirkefabrikation," ellemiker - Zeituflg, Nov. 6, 1920, In addition to these changes, the crumb XLIV, 833-34; Nov. 11, 1920, 845-47. loses some of its power to swell when im- 234 THE STALE-BREAD PROBLEM mersed in water; it swells less than when an atmosphere saturated with water vapor in fresh.l At the same time, its soluble-starch which, obviously, it cannot lose moistUre. content decreases.2 These changes occur in Housewives, of course, had known from time rye as well as in wheaten hread. They do not, immemorial that stale bread could be fresh­ according to Katz,3 occur in baked products ened by warming. Boussingault showed that of low-moisture content, like zwieback, Swed­ this took place at 50° to 60° C. and could be ish bread, and mazoth. To the change in tex­ repeated indefinitely. He heated stale bread ture of crumb, its toughening and hardening in a tight vessel till fresh, then allowed it to and their causes, the remainder of this study cool and grow stale again, and found that is devoted. under these conditions, which prevented dry­ ing out, the cycle could be repeated many HISTORY OF BREAD-STALING THEORIES times. He advanced the hypothesis that stale Until 1852, it was generally believed that bread is not different from fresh because it the growing stale of bread was due to drying contains less water, but rather because of a out. In that year BoussingauW demonstrated change in the peculiar molecular state of its by chemical analysis that bread turns stale substance that begins when it cools and con­ long before it has lost any appreciable amount tinues to develop more and more with time of moisture. He showed that it turns stale in so long as the temperature does not rise above a certain level. 1 K. B. Lehmann, "Hygienische Studien iiber Mehl­ Von Bibra reached a similar view and ex­ und Brot. Theil V; Beitrage zur physikalischen Be­ 5 schaffenheit des Brotcs," Arclliv fur Hygiene, 1894, XXI, tended his observations to rye bread. Others 213-67. later did the same for barley bread. In addi­ 2 L. Lindet, "Sur les etats que presente l'amidon tion, von Bibra showed that bread can no dans Ie pain tendre et dans Ie pain rassis," Bulletin de longer be freshened by warming if its mois­ la Societe cllimique de Paris, May 23, 1902, Serie III, XXVII, 634-39. ture content has dropped to 30 per cent or 3 J. R. Katz, "Gelatinization and Retrogradation of less,a but that bread as dryas this could be Starch in the Bread Staling Process," in A Compre­ freshened if it was moistened before it was lIensive Survey of Starcll ClIemistry, compiled and warmed Up.7 edited by R. P. Walton (New York, Chemical Catalog Company, 1928), Vol. I, Part 1, p. 103. It is an old belief of practical bakers that a

;I, Boussingault, "De la transformation du pain ten­ long dough-fermentation period leads to bread dre en pain rassis," in his Agronomie, ClIimie agricole, that keeps fresh well. Graeger8 tested this et PlIysiologie (Paris, Gauthier-Villars, 2d edition, 1874), V, 416-17. notion and reached the conclusion that exten­ G E. von Bibra, Getreidearten und das Brot (Niirn­ sion of the fermentation time beyond three berg, 1861), p. 490. hours at 25° C. did not lead to bread of better 6 In this connection, it is perhaps significant that keeping quality even though longer fermen­ native wheat-starch granules when fully hydrated contain about 30 per cent (according to Rodewald, 36 tation increases the acidity of the dough. Per­ per cent) of water of hydration. Such water is of haps, as pointed out above, a long fermenta­ course less easily set free by warming than water not tion has favorable effects on the keeping qual­ thus combined. Bread may range in water content from about 34 per cent for fine wheaten rolls to about ity of bread, because of its effects upon flavor 42 per cent for graham bread and 49 per cent for whole rather than texture. coarse rye bread. Cf. AIsberg, "Starch and Flour Neither Boussingault9 nor von Bibralo en­ Quality." deavored to analyze the process in detail. 7 Cf. also A. Maurizio, Getreidenallrung im Wan­ del der Zeiten (Zurich, Orell Fiiszli, 1916), p. 215; Von Bibra contented himself with the view cited in A. Maurizio, Die Nallrungsmittel ails Gelreide that in warm bread the starch, nitrogenous (Berlin, Parey, 2d edition, 1924), I, 368. substance, and water are combined in a pecu­ 8 Cited by von Bibra, op. cit., p. 411. liar molecular condition which is gradually 90p. cit. lOOp. cit. changed on cooling and can be restored by 11 E. N. Horsford, "Report on Vienna Bread," in Re­ warming. ports of tlle Commissioners of tlle United States to tlle Horsfordll was apparently the first to sug­ International Exllibition Held at Vienna, 1873, edited gest that the growing stale of bread is due to by R. H. Thurston (Washington, Government Printing Office, 1876), Vol. II, B, pp. 1-122, especially pp. 92, 96. a change in distribution of water between ll/STORY OF BREAD-STALING THEORIES 23;') starch and gluten and that the change of tex­ ously filled with water, are formed. If liquid ture is the result of change in the condition of is filtered through a slice of crumb, it flows the starch. Most hypotheses advanced since through fresh bread more rapidly than his time have been based upon such assump­ through stale. However, stale bread sucks up tions. "The gluten, which is mixed with it liquid by capillarity more readily than fresh [the starch] in the crumb of bread, and which bread. Pieces of stale crumb placed in water may be conceived to be continuous, however imbibe it about as rapidly during the first thin throughout the wall of the cell, has been, few minutes as fresh bread. After ten min­ by the process of baking, dehydrated; that is, utes, stale bread drops behind fresh and the heat to which it has been subjected has reaches its maximum in half an hour, whereas driven out a certain amount of water, which fresh bread continues to imbibe for some chemically sustains something like the same time. In one of his experiments, fresh wheat relation to the gluten from which it has been bread imbibed 289 per cent, whereas stale im­ expelled that the water expelled by heat from bibed only 153 per cent. Pieces of stale crumb alum-crystals sustains to the original body of keep their shape for weeks when stored under alum. This is the condition of the gluten from water, whereas fresh bread disintegrates. the crumb in the interior of the loaf at the in­ Pieces of fresh crumb may swell by imbibition stant of its removal from the oven. On drying, as much as 16 per cent, but stale bread only it abstracts water from the starch with which 6 per cent. Crumb merely stale and crumb it is coated, or intimately mixed, as the roasted air-dry with only 12 per cent of moisture alum absorbs the water that is sprinkled upon behave in the same way. When the imbibition it. The starch by this process being dried and experiments were made in water heated to stiffened, gives its support to the wall of the 40° to 60° C., the stale crumb imbibed almost cell, and renders the texture of the stale loaf as much as fresh. Warming up stale bread more firm than that of the fresh loaf. .... The restores its imbibition capacity. Lehmann did gluten of the crumb-walls of stale bread which not offer a new hypothesis. He was content are stiff and brittle is dehydrated by the heat with the hypothesis of Boussingault and von in freshening, and the water of hydration Bibra, that water is held in different ways in driven out softens the glacial, horny starch fresh and stale bread. He believed that a sub­ which coats and penetrates the gluten. Thus stance is formed in stale bread, by unknown softened, the crumb is more palatable, because molecular processes, which swells with diffi­ it is in condition to be dissolved by the saliva, culty in cold water, but may be transformed and tasted. On cooling, the water is withdrawn by heat into the for;m in which it swells in from the starch, which is thereby rendered water and occurs in fresh bread. stiff, and restored to the gluten, and the bread Boutroux2 distinguished two stages in the becomes stale." process. During the first, the bread cools off Lehmann1 compared the imbibing power of to the temperature of the environment; dur­ fresh and of stale bread. He found that pieces ing the second, it continues to grow stale if of crumb shrink in drying, the shrinkage the temperature is not changed. Although the stopping in four days-much earlier than the loss of water is at first but slight, this loss has water loss. Shrinkage and water loss are most nevertheless great significance. Boutroux as­ rapid the first day. In shrinking, the pores sumed that during baking the crust reaches contract but the pore space increases some­ a temperature of about 300° C. The air of the what nevertheless because new pores, previ- oven is hoUer than the crumb; therefore some lOp. cit. of the water of the crust is driven into the 2 L. Boutrotlx, Le pain et 1a panification (Paris, interior of the bread and the crumb does not Bailliere, 1897). give off water to the air through the crust. If a Cited by Boutroux, op. cit. Ratz. (Het Oudbakken Worden van het Brood in Verband met het Vraagstuk baking lasts some time, then the loss of water van den NacMarbeid der Balel,ers, Part 1, p. 9) takes from the inside of the loaf is only attributable the same position. He was unable with certainty to establish a loss of water from the crumb during bak­ to the increase in thickness of the crust. This ing. The crust protects it. is the reason why, Boutroux asserts, Balland3 236 TIlE STALE-BREAD PROHI,EM

and others found just as much water in fully LindeU confirmed some of the observations baked crumb as in dough ready for the oven. of Boutroux and introduced the idea that the After removal of the loaf from the oven, growing stale of bread is due to retrograda­ the crust cools off first and soon is warmer tion of the starch, i.e., its conversion into a than the air, but cooler than the crumb, a less soluble form with the setting free of mois­ condition which is the opposite of that which ture. He found, however, that it was soluble obtains in the oven. The crust then gives off a starch3 rather than amylodextrin, as Bou­ little moisture to the surrounding air while troux assumed, that is formed under the in­ surplus water of the crumb is condensed in fluence of the heat of the oven. He noted that the crust and held there. This redistribution with time the amount of soluble starch in of the water of the loaf may take place with­ crumb decreases and it is this that he termed out much loss of moisture and yet profoundly "retrogradation." He published data on only affect the texture of the crumb. The crust is three experiments and among these there was softened by the water that wanders to it from only one adequate control, the determination the crumb. The crumb becomes harder be­ of soluble starch in bread an hour old. It is cause of loss of water to the crust. When stale only in this single analysis (whether done in bread is returned to the oven, the process is duplicate is not stated) that a large difference reversed and the crust returns again to the in soluble starch content between fresh and crumb most of the water it had absorbed from stale bread is shown. In another experiment, the crumb. the difference between 8-hour-old and 48- Boutroux made one other assumption: it is hour-old bread was 2.5 per cent; and in the that bread contains a supersaturated solution third, there was no significant difference at of amylodextrin formed from starch. Amylo­ all. The methods used were not given. dextrin is a substance separated by Lintner But, according to Lindet, this is not the and Diilll from among the products of the whole story: change in the gelatinized starch digestion of starch by malt diastase. It is is also involved. By a method which is obvi­ freely soluble in hot but not in cold water and ously only roughly quantitative, he estimated readily forms supersaturated solutions. Bou­ the water absorbed by a gram of starch in troux assumed, without experimental evi­ bread of different ages. From his results, he dence, that such a supersaturated solution drew the conclusion that with age the gela­ exists in bread, that on cooling amylodextrin tinized starch granule imbibes less and less separates as a solid, and that it is this sepa­ water. It retains six times its volume of water ration that gives stale bread its texture. How­ when the bread is warm; when it becomes ever, no one has actually found amylodextrin stale, it imbibes two times less. He assumed in bread crumb. Nevertheless, Boutroux seems that the starch contracts and becomes horny to have been the first to assume that staleness (raccorni) with time because it becomes less is due to the separation in insoluble form of a permeable. derivative of starch, even though he was mis­ Roux1 believed that in retrogradation some taken in the character of this derivative. This starch is converted into starch cellulose (amy­ assumption in one form or another has con­ locellulose), which is insoluble and therefore stituted the center of most hypotheses since. alters the texture of starch pastes. Roux ex­ amined bread to learn whether the starch of 1 C. J. Lintner and G. Dull, "Ueber den Abbau del' Starke unter dcm Einflusse del' Diastasewirlmng," Be­ bread retrogrades in this way with age. He ricllte der Deutschen cllemiscllen Gesellschaft, October found it retrogrades but slightly. In fresh 1893, XXVI, 2533-47. 20p. cit. bread, there is no so-called amylocellulose, a The soluble starch found in fresh bread is ~-amy­ whereas it can be detected qualitatively after lose (see ahove)-not the soluble starch so-called ob­ a few hours and it increases in time. Roux tained by partial decomposition of natural starch with acid or other powerful reagent. reached no positive conclusions and his ap­ 1 E. Roux, "Sur I'etat de I'amidon dans Ie pain ras­ proach is no longer significant, for views re­ sis," Comptes rendus llebdomadaires des seances de garding retrogradation and amylocellulose [,Academie des Sciences, May 30, 1904, CXXXVIII, 1:156-58. have changed. It is doubtful that there is any HISTORY OF BREAD-STALING THEORIES 237 slich substance as amylocellulose in wheat temperature. The rate of growing stale is starch at all. accelerated as the temperature drops and In 1912, J. R. Katz! and also E. VerschafIelP passes through a maximum at _20 to -30 C. made reports to the Dutch Foodstuff Congress As the temperature is lowered further, bread meeting in Rotterdam on the stale-bread prob­ goes stale less and less rapidly, and at very lem, for this had become a critical question in low temperatures, as at the temperature of Holland in connection with the night work of liquid air, it remains fresh indefinitely. bakers. In 1913, Katz3 presented evidence that Katz1 followed the rate of growing stale by there is a physico-chemical equilibrium in the following three methods: crumb such that at higher temperatures (50 0 1. By testing crumbliness and hardness to 100 0 C.) fresh bread is the stable form, with the finger. whereas at room temperature (0 0 to 25 0 C.) 2. By changes in the swelling power based stale bread is the labile, unstable form. Crumb on the observations of Balland, Lindet, Leh­ stored without moisture loss at room tem­ mann, and others that stale crumb swells less perature becomes stale within 24 hours, in water than fresh. "Ten grams of bread whereas, if stored at 60 0 to 70 0 C., it remains crumb together with an excess of water are entirely fresh and does not change in taste or passed through fine bolting cloth (80 mesh odor. The equilibrium is shifted with the per cm.). The volume of the liquid (which is saturated with toluene in order to prevent fer­ 1 "Rapport voor de Voedingsmiddelconferentie te mentation) is raised to 250 c.cm. and the mix­ Hotterdam in 1912," published in Chemisch Weekblad and Pharmaceutisch Weekblad, .June 4, 1912; cited in ture allowed to settle in a graduated glass of Katz, Het Oudbakken Worden van het Brood in Ver­ 250 c.cm. capacity. After 24 hours the volume band met het Vraagstuk van den Nachtarbeid der Bak­ of the decantate or deposit is read off. Upon kers, Part 2, p. 3. shaking again, another 24 hours is allowed 2 "Rapport uitgebracht op de Voedingsmiddelcon­ ferentie te Rotterdam Juli 1912," published in Clzem­ for settling, a second reading made and the iscIl Weekblad and Pharmaceutisch Weekblad, De­ mean of the two readings taken. The volume cember 1912; cited in Katz, Het Oudbakken Worden Iwn het Brood in Verband met het Vraagstuk van den of the decantate is shown to be considerably Nachtarbeid der Bakkers, Part 2, p. 15. larger for fresh bread than for stale bread, for 3 J. R. Katz, "Uber die Analogie zwischen Quellen instance, 52 c.cm. compared with 34 c.cm. !lnd Mischen, eine Experimentaluntersuchung iiber die The volume of decantate is obviously a suit­ Gesetz del' Quellung im Wasser," Zeitscllrift ftir Elek­ trocllemie, Sept. 15, 1911, XVII, 800-805; "Die Ursachen able criterion for determination of the swell­ des Altbacl!enwerdens des Brotes vom physikalisch­ ing power."5 chemischen Standpunkte betrachtet"; "Die Ursache 3. "The quantity of soluble amylose, which des Altbackenwerdens del' Brotkruste und die Moglich­ keit, diese Veriindcrung zu verhiiten," ibid., Sept. 1, may be extracted from bread is larger for 19'13, XIX 663-67. fresh bread than for stale bread .... This 4 "Gelatinization and Retrogradation of Starch in quantity of soluble amylose, extractable from the Bread Staling Process"; Het Oudbakken Worden van het Brood in Verband met het Vraagstllk van den bread, is a function of the degree of com­ Nachtarbeid der Bakkers .. "Ober das Altbackenwerden minution of the bread. Hence, it is necessary des Brotes und die Moglichkeit, diese Veriindcrung to work always under the same conditions and hintunzuhalten," ZeitscJlrift fiir das gesamte Getreide­ Miililen- und Biickereiwesen, March 1934, XXI, 63-68. then readily comparable figures may be ob­ G Katz, "Gelatinization and Retrogradation of Starch tained. In practice the determination was so in the Bread Staling Process," p. 102. In an inves­ carried out that the clear liquid above the tigation as yet unpublished, M. Lopin found at the decantate, in the determination of swelling ~?ood Research Institute that the method is improved If 25 per cent alcohol be used instead of water. Sedi­ power, was poured off, filtered clear, evapo­ mentation occurs much more rapidly and readings are rated to a small volume and precipitated with sharper. Whether the method in this modification is excess alcohol, the resulting precipitate being as delicate as in the form introduced by Ratz was not studied. Incidentally, it may be stated that, whether collected in a tared filter and dried and water or weak alcohol be used, the uppermost layel' weighed."6 of the sediment consists mainly of starch and differs in gross appearance with the age of the bread. According to Katz, the second method is

, 0 Katz, "Gelatinization and Retrogradation of Starch the most satisfactory for all-round purposes. III the Bread Staling Pl'Ocess," p. 102. Hardness, swelling, and quantity of soluble 238 THE STALE-BREAD PROBLEM

starch may be measured withsutlicient accu­ with the well-knQwn phenomenon that a loaf racy; crumbliness cannot. The rate at which of bread shrinks as it ages,B and with the obser­ staleness proceeds can be determined accu­ vation of Lehmann4 that, though the pores of rately.l In Dutch bread, hardness, swelling fresh bread shrink, new pores are formed by power, and quantity of soluble starch nearly shrinkage of the bread mass, so that the sum reach the values found in fully stale bread total of the volume of the pores of stale bread within 9 to 10 hours, whereas crumbliness is is moderately increased. definitely present only after 24 hours. VerschaffeIt and van Teutem reported, The microscopic appearance of fresh and moreover, that bread which is about nine stale bread, according to Katz, explains this hours old and therefore, according to Katz, lag in the onset of crumbliness, as is shown no more crumbly than fresh bread, though in by the investigations of Verschaffelt and van respect to its other properties stale, has the Teutem2 made at the instigation of Katz. In microscopic appearance of fresh bread. The fresh-bread crumb, each starch granule is development of the air spaces apparently par­ completely surrounded by gluten, and this glu­ allels the development of crumbliness and not ten capsule fits the granule as closely as a the development of the other characters of glove. No soluble starch is found outside the stale bread, viz., the development of hardness, granules. In stale bread, no precipitates are loss of swelling power, and reduction of sol­ formed anywhere, but the outlines of the uble amylose content. According to Katz, this granules become sharper because of the de­ disparity depends upon the time required for velopment of fine air channels between the water to diffuse from the starch to the gluten. starch granules and the gluten matrix which Verschaffelt and van Teutem found that the surrounds them. For the larger granules, the outlines of the starch granules in stale bread width of the air spaces is from about one­ had become not merely sharper, but also twentieth to one-tenth the diameter of the somewhat crenulated (zaclcig) and irregular. granules; and this is true for bread that has Moreover, they believe that in fresh bread the not suffered loss of moisture. The appearance granules of starch are under strain. If a thin is such as one would expect if, by shrinkage lamella of fresh-bread crumb be placed in a of starch and gluten, these elements of the little water on a microscope slide, covered crumb had become separated from one an­ with a cover glass, and pressure immediately other. exerted on the cover glass, some granules near These observations are in entire harmony the thin edge of the lamella may be observed to free themselves with a jerk, provided ex­

1 J. R. Katz, "De snelheid van het oudbakken worden amination be made at once after putting in the van brood." (Akademie van Wetenschappen te Amster­ water. From stale bread, they are not freed dam, Verslag, 1914, deel 23, p. 652-655); cit cd by Walton, op. cit., Part 2, p. 77; "Das Altbackenwcrden with a jerk. dcr Brotkrumc vom physiologisch-chcmischen Stand­ Katz found that an excess of water inhibits punktc bctrachtet. I," Hoppe-Seyler's Zeitschrift filr the aging of bread. Fresh bread suspended physiologische Chemie, Oct. 19, 1915, XCV, 104-29; II, ibid., pp. 136-46; III, ibid., pp. 147-51. in water with a disinfectant to prevent fer­ 2 E. Verschaffelt and E. van Teutem, "Die Xnderung mentation and putrefaction retains the swell­ del' mikroskopischen Struktur des Brotes beim Alt­ ing power of fresh bread, and stale bread backenwerden," Zeitschrift filr physiologische Chemie, October 1915, XCV, 130-35. similarly stored does not change its swelling power. 3 K. Mohs, Mehlchemie, Neue Erkenntnisse auf dem Gebiete der Milllerei und Backerei (Dresden and Leip­ Katz holds the view that the changes starch zig, Steinkopff, 3d edition, 19i1l). undergoes in bread with age are the same all 40p. cit. starches undergo when they are gelatinized r,.J. R. Katz, "Het oudbakhen worden is een veran­ 5 dering die niet enkel bij tarwe- en roggenzetmeel with the same amount of water as in bread. voorkomt doch bij aIle zetmeelsoorten, maar die In bread, starch is in first-degree gelatiniza­ toevallig aIleen bij tarwe en rogge tot practisch be­ tion (see above). He therefore concludes that langrijke rcsultaten voect." (Akademie van Weten­ scbappen te Amsterdam, Verslag, 1914, deel 23, p. 655- the growing stale of bread is the expression 658); cited by Walton, op. cit., Part 2, p. 77. of the change in the starch. This change he HISTORY OF BREAD-STALING THEORIES 239 identifies with retrogradation. It is accom­ is an internal change of state of this starch panied by some redistribution of water. gel which consists of a lessening of its degree Hetrograded starch holds water less firmly of dispersion and dehydration, with resulting and in consequence moisture wanders from extrusion of liquid, or syneresis (see second lhe retrograded starch to the crust and to section). The syneresis of aging bread is the other components of the crumb, prin­ plainly to be observed when it is protected in cipally the gluten. This change in the starch a tin can from evaporation. According to is a physico-chemical reaction with an equi­ Ostwald, after one or two days the bread feels librium characteristic of such reactions and damp, although no moisture fTom without has obeying physico-chemical laws. In the process access to it. In fact, the dampness is derived of retrogradation, the starch granules shrink from the interior of the bread; the aging away from the gluten so that microscopic starch gel is no lopger able to hold as much fissures are produced between many of the water. Water is set free from it by syneresis starch granules and the gluten network. and brought to the surface. By warming for When bread is freshened by warming, the a short time-exactly as with a synerizing process of retrogradation is reversed and gelatin jelly-water is again taken up by the moisture wanders back into the starch gran­ starch gel, at least in part, and thereby the ules whereby they are softened. Stale bread former state is again restored. is hard and tough, because retrograded starch This view of the processes that go on in is harder and tougher than starch freshly bread when it grows stale, viz., that they de­ gelatinized to the first degree. pend upon syneresis, is accepted, at least in Katz holds the opinion, moreover, that the part, by a number of other investigators, for changes in swelling power of gelatinized example Whymper,2 while some investigators starch and the lessening of soluble starch in hold some of the views of Katz combined with it are quite unrelated processes, for he has the idea of Ostwald. found that they proceed at quite unrelated Since the publication of his large mono­ rates in bread to which aldehyde had been graph in 1917,3 Katz has modified his views added. He believes they are to be explained as to harmonize them with his own observations retrogradation (see above). by means of the X-ray and those of others. Ostwald,l while agreeing with Katz that it These findings, in so far as they are pertinent is change in the starch that causes bread to to the present inquiry, have been described grow stale, rejected Katz's hypothesis that in the preceding section. His present view this change is retrogradation. He interpreted seems to be essentially identical with that he the phenomenon as follows: The baking of formerly held, except with regard to the na­ bread depends upon the formation of starch ture of the change in the starch.4 Bread, he gel of a definite structure; its growing stale finds, shows the same changes in X-ray pat­ tern as starch, and in bread these changes run 1 W. Ostwald, Die Welt der vernaehliissiglen Dimen­ parallel with the change in swelling power sionen (Dresden and Leipzig, Steinkopff, 1915). and amylose content of the crumb. His views ~ R. Whymper, The Conditions That Govern Stale­ ness in Bread (reprinted from the British Baker), on the shift of moisture within the crumb 1!J19; "Colloid Problems in Bread-Malting," in "Col­ apparently remain unchanged, but he no loid Chemistry and Its General and Industrial Appli­ longer regards the process of retrogradation cations, Third Report of the Committee .... ," British Association for the AdlJanrement of Science, Report as involving a simple homogeneous equi­ of the EiglltlJ-eighth Meeting, Cardiff-1920, AZlgZlst librium reaction. He now tends to the view 24-28 (London, Murray, 1920), Appendix, pp. 61-74. that the process is much more complex and 3 II et OZldbakken Worden van het Brood in Verband involves a heterogeneous equilibrium. At the met l,ei VraagstZlk van den Naehlarbeid der Bakkers. 1.J. H. Katz, "Abhandlungen zur physikalischen same time, he has introduced a new nonchem­ Chemic del' Starke und der Brotbereitung. I. i}ber die ical factor, the structure of the starch granule Anderungen im Riintgcnspektrum del' Starke beim itself. The significance of this interpretation Bac~en und beim Altbackenwerden des Brotes," Zeit­ srllrlft fur phllsikalisclle Chemie, Abteilung A, Sep­ of the known facts has been discussed in the tember, 1930, CL, 37-59. preceding section. 240 THE STALE-BREAD PROBLEM

CRITIQUE OF COMPETING HYPOTHESES interior of loaves in the oven. Now, as we have seen, starch in first-degree gelatinization docs We see then that all the hypotheses hitherto not extrude water within a period so brief as advanced in so far as they are more specific that required for bread to grow stale, though than that of Boussingault and von Bibra make it may retrograde in that it becomes more staleness depend upon a shift in moisture from opaque and more firm, and changes its X-ray one element of the crumb to another. Hors­ pattern (Katz). It seems reasonably certain, ford was the first to advance this idea. He therefore, that if there is a shift of moisture assumed that as the loaf cooled the gluten gave from starch to gluten it cannot be due to ofT moisture to the starch, a process that was extrusion of liquid water as in retrogradation reversed when stale bread was freshened by of starch under the conditions employed by warming. Apparently, according to his hy­ French investigators. pothesis, these two ingredients are assumed However, there might nevertheless be a to share more or less equally in the process of shift in moisture from starch to gluten as growing stale. For Horsford, the whole ques­ the loaf ages without the physical transfer of tion was apparently merely a matter of a fluid water. This transfer might be in the shift in the relation of the vapor pressure of form of water vapor. But in order that this the gluten gel to that of the starch gel with may happen, the vapor pressure of the starch the temperature, although he does not use must change relative to that of the gluten. the term vapor pressure. At higher tempera­ We are justified in assuming that the vapor tures, the vapor pressure of gluten gel was, he pressure of the gluten remains constant and assumed, greater than that of starch gel and, practically that of water, for the gluten, hav­ therefore, water vapor shifted from the gluten ing been coagulated, has lost most of its great to the starch, making the starch softer and imbibing power for water. The vapor pressure more elastic, which expressed itself in the of starch in first-degree gelatinization is not characteristics of fresh bread. At lower tem­ known, but it is probably not greater than peratures, the reverse obtains. Unfortunately, that of water. If it were, the vapor pressure Horsford's experiments in support of his hy­ of bread would be greater than that of water, pothesis were neither appropriate nor signifi­ for starch composes over four-fifths of the cant, for he took no account of the fact that solid matter of bread. As a matter of fact, during baking gluten is coagulated and loses Katzl and recently Plattz have shown that the much of its capacity to absorb water. vapor pressure of crumb is the same as that French investigators, notably Lindet and of water. A transfer of water vapor from Roux, went a step further and assumed that starch to gluten is therefore improbable. it was the starch primarily that, by retrograd­ There is no good basis for the assumption of ing, set free water which wandered to the French investigators that, in the aging of other components of the loaf. They reasoned crumb, starch loses water to the gluten. by analogy from the behavior of starch pastes The French investigators, however, dis­ and solution which on aging in fact separate covered one piece of evidence which is not moisture. It is of course impossible to dem­ analogy, the fact that the amount of soluble onstrate this phenomenon in bread. But bread starch which can be extracted from crumb and the starch pastes or solutions with which grows less as bread grows stale, a fact French investigators studied retrogradations abundantly confirmed by Katz, Whymper, and are not comparable. Their pastes were com­ others. The significance of this phenomenon paratively rich in water so that the starch has already been discussed, hut merits some in them was in a state of second-degree gelat­ further consideration. inization and not in first-degree, as Katz has Field3 and the writer1 have found that found it to be in bread. The solutions they 1 "De snelheid van het oudbaI

1 D. Straup, "The Flocculation of Gelatin at the that gelatinized starch (two parts water, one Isoelectric Point," Journal of General Physiology. part starch) is amorphous when warm and May 20, 1931. XIV. 643-60. partly crystallizes when cooled. He finds that 2.J. R. Katz, "Abhandlungen zur physikalischen Chemie del' Starke und del' Brotbercitung. XX. Ober a solution of commercial soluble starch ge­ den Zusammcnhang del' Xnderung del' Starke beim latinizes because on cooling it crystallizes out Altbackenwerden des Brotes und beim Retrogradieren into tiny crystals which are felted together von Stiirkeldeistcr," Zeitschrift filr physilwlisclle Chemie, Abtcilung A, August 1934, CLXIX, 321-38. (ver{ilzt). Certainly mere crystallization is 3 J. R. Katz and J. C. Derksen, "Abhandlungen zur not, in the ordinary meaning of the term, a physikalischen Chemie del' Stiirke und del' Brot­ chemical reaction. He further concludes that bereitung. XIV. 1st die Starke im Starkeldeister one of the consequences of the changes in the ~ristallinisch odeI' amorph?" Zeitschrift filr pllysikal­ lsclle Cllemie, Abteilung A, November 1933, CLXVII, starch is that it gives oIT moisture to the 129-36; J. C. Derksen and J. R. Katz, "Roentgenspek­ gluten. This, as has been pointed out already, trographischc Beobachtungen libel' das Gelatinieren von Starkesolen," Recueil des Travaux ClIimiques des is at least unproved. Moisture might wander PUllS-Bas. 1932, LI, 523-26. from the starch to the gluten either as liquid 242 TIlE STALE-BREAD PROBLEM extruded by the retrograding granules or as rize. Perhaps the gluten too shrinks and be­ vapor. It is unlikely that it wanders in the comes harder, because it is losing moisture to form of liquid, since very concentrated gels either the starch or the crumb solution, or extrude water either very slowly or not at all. both. Thus strains are set up at the surfaces If it wanders as vapor, it must be to some other where the gluten and starch meet, which ulti­ crumb component with a lower vapor tension mately cause them to separate. The bread than that of first-degree gelatinized starch. then becomes crumbly. Before this stage is Certainly gluten is not such a substance. Als­ reached, the starch begins to retrograde. The berg and GrifIing' have shown that the swell­ granules become opaquer, whiter, harder, and ing capacity of coagulaled gluten, and hence firmer, and the bread is stale. its avidity for moisture, is slight. There re­ While all this is going on, the loaf as a mains the liquid held by neither starch nor whole has been losing some moisture. The gluten in which salts, sugar, etc., are dissolved, crust which is drier than the crumb competes and it is indeed possible that this very concen­ with the starch of the crumb for the moisture trated solution may take up moisture from of the loaf. It extracts some water from the both the starch and the gluten as the bread crumb on its inner surface and loses some ages. It is not likely, however, that the effect water to the atmosphere on its outer surface. is great-otherwise bread would not have the And thus the loaf ultimately dries out in ad­ same vapor tension as water. dition to growing stale. When the bread is But it is not at all necessary to assume that freshened by warming, the starch gel becomes there is a shift in moisture. It is possible soft again and increases a little in volume­ without in the least questioning the important possibly takes up a little water from the gluten flndings of Katz to interpret them somewhat and the bread becomes fresh, for the starch is difTerently. We may then regard the growing no longer hard and tough. stale of bread as taking the following course. This interpretation of the facts thus far In the oven, the gluten is coagulated and loses established has the advantages over others most of its power to hold water. The starch that have been suggested in the following granules become incompletely gelatinized, respects. It makes no assumptions regard­ taking up what water they can from their ing the chemical nature of the change in the surroundings. A part of this water is derived starch. It does not assume that starch gel has from the coagulating gluten which is no longer properties not found in many other colloid able to hold all it held in the dough because gels. It is not inconsistent with the known it is coagulated. As the bread leaves the oven, facts of retrogradation-a phenomenon that the moisture is distributed through the loaf in has its counterpart in gels other than those of the following manner: some is in the form of starch. vapor filling the pores of the crumb; some Whether the starch of aging bread merely is still in the gluten; some is serving as a sol­ undergoes the colloid-chemical changes char­ vent for salts, sugar, etc., in the crumb solu­ acteristic of many other gels that set when tion; some is imbibed in the partially gelatin­ cooled and soften when warmed, or whether it ized starch. In this state the starch is soft and undergoes some chemical change, as Katz sup­ the gluten tender. As the bread cools, the soft poses and as do those who write of retrogra­ starch jelly sets and becomes a stiff but still dation, is not an academic but a very practical elastic gel which contains less water than is question. If we have to deal with a chemical necessary for complete gelatinization. In the reaction involving an equilibrium, then it process of setting and for some time after­ should be possible in theory to find a sub­ ward, the starch gel shrinks a little as it cools, stance, a catalyst, that is able to shift this a phenomenon very common in the setting and equilibrium in such a manner that the equilib­ aging of warm gels whether or not they syne- rium is the same at room temperature as at 55° C. Then bread would not go stale under 1 C. L. AIsberg and E. P. Griffing, "The Heat Coagu­ ordinary conditions of storage. On the con­ lation of Gluten," Cereal Chemis/ru, November 1927, IV, 411-2il. trary, if the change in the starch is a purely PROLONGING TIlB LIFE OF BREAD colloidal phenomenon and therefore not in­ not exactly run parallel with the changes in volving any chemical reaction in thc strict the starch granules. sense of the word, then it is idle to search for The sedimentation test is the one most used. a catalyst to delay the onset of staleness. This Undoubtedly the results obtained with it give process in that event could be slowed or in­ a good index to the condition of the bread. hibited only by means which inhibit colloidal Unfortunately, as Katz2 reports, and as the changes, and the search for a method to pro­ writer has also found, it does not show that duce stale-proof bread would have to follow any of the procedures of manufacture, which quite different paths. the baking trade is fully agreed prolong the life of bread (see below), delay the aging of PUOLONGING THE LIFE OF BUEAI) the starch granules of the crumb. Yet it can­ While the analysis of the known phenomena not be doubted that some of these practical presented in the foregoing sections clearly procedures do have the effect claimed for shows that there is still much to learn regard­ them. The explanation probably is that the ing the mechanism responsible for the changes sedimentation test tells the state of the starch in bread as it ages, the known facts indicate correctly but that this is probably not the that the commercial life of bread may be pro­ whole story. longed either by special methods of handling If, for example, the quality of the gluten or and storing after the bread has left the oven, the changes in the distribution of the mois­ or by methods of manufacture which pro­ ture in the loaf are of importance in deter­ duce a loaf of inherently long life. Let us now mining the texture of crumb, the sedimenta­ consider each of these groups of methods tion test might indicate the age of the bread separately, but before doing so let us first with considerable exactness and yet not indi­ consider the methods by which the degree cate with equal exactness the physical condi­ of staleness may be measured with some tion of the crumb. It is not impossible, as exactness. Katz points out, that the way the fermentation These methods as developed and refined by of the dough is conducted, the amount and Katz have been described in the section on the quality of the yeast, the amount and quality "Structure and Behavior of Starch Grains" : of the gluten, the presence of gelatinized 1. The estimation of crumbliness or com­ starch, of milk, and of shortening, etc., do not pressibility of crumb by some sort of me­ delay the changes in the starch but in some chanical testing instrument. way mask their effects so that despite harden­ 2. The quantitative estimation of the sol­ ing of the starch granules the crumb as a uble starch in crumb. whole still feels soft for a time. If this is the 3. The observation under standard condi­ case, the sedimentation test would permit tions of the sedimentation volume of crumb rather exact comparison between two loaves pulped in water. manufactured in the same way but might be For the estimation of compressibility, satis­ less satisfactory in comparing two loaves of factory devices have been invented by a num­ different types to learn which remains fresh her of students,! but they do not seem as yet the longer, if other factors in addition to to have been employed extensively. starch changes are concerned in the aging of The quantitative estimation of soluble bread. The sedimentation test would not starch in crumb is difficult and time consum­ measure, for example, differences in moisture ing. The objections to it have already been distribution or differences in gluten texture if discussed. The soluble-starch content does such there be. The next step in the developing of methods 1.J. R. Katz, "What Is thc Fundamcntal Change in the Staling of the Bread Crumh?" Balcers Weelcill, Dec. for testing stale bread would seem to be the 1, 1934, LXXXIV, 31-34; Platt, op. cil.; L. H. Bailey, comparison of the sedimentation test with the ".~. Simple Apparatus for Measuring the Compl'cssi­ compressibility test using different types of IJllIty of Baked Products," ibid., .July 1930, pp. 340-41. bread; in other words, the checking of the 2 Bel Oudbalclcen Worden van lIef Brood in Verband mel lief Vraaf]stulc van den Naclltarbeid der Balclcers. indirect sedimentation method against the di- 244 THB STALE-BREAD PROBl,EM rect measurement of one of the physical traits out complaint. With the great improvements of the crumb. Some work has been done in in air-conditioning of recent years, there is this direction but its volume is not yet ade­ no doubt that this apparatus can be improved quate.I upon; but in America the method would he Let us now turn to the prolonging of the of little service to wholesale bakers, who must life of bread by methods of handling and stor­ deliver to the retailer. It might, however, he ing after the loaf has left the oven. useful to retail bakers, but these need it less Bread may be kept fresh by freezing. A than wholesalers because they are in good temperature of _6° C. delays the onset of position to adjust production to demand. It staleness and a temperature of _10° to _20° is possible that inexpensive foolproof devices C. prevents it altogether. It is not yet feasible of this sort might be placed in retail groceries under ordinary commercial conditions to to good advantage, but in the aggregate this freeze bread because of the expense and be­ would require a large investment on the part cause of the difficulties that arise in thawing. of the wholesaler. It would not relieve him of This takes much time, and moisture condenses the necessity of baking a loaf with a long life, on the crust which makes it soft like that of for the growing stale of the crumb is not de­ stale bread. To avoid this the bread must be layed-the crispiness of the crust is merely thawed out in dry air. retained for a few hours longer. . Bread may be held at a temperature above We must therefore examine manufactur­ 55° C. The objections to this procedure are ing methods that have been suggested to pro­ that the crust becomes hard and dry, and bac­ long the life of the loaf. These may be grouped teria are likely to develop inside the bread. If in two general categories: processes and in­ drying out is prevented by holding in a sealed gredients. Among manufacturing processes chamber, the crust becomes soft and leathery that are said to prolong the life of bread are and the crumb may acquire a crusty flavor. the following: No practical method seems as yet to have been a) Use of high-speed mixer. devised to keep bread fresh by holding at an b) Fermentation at low temperature, say elevated temperature. 220 to 26° C. The liquid used in doughing Since consumers judge bread when they should not be warm, say not over 25° C. It purchase it in part by the condition of the should of course be cooler if a high-speed crust, and since the crust becomes soft before mixer is used. the crumb is noticeably stale, Katz has pro­ c) Fermentation as long as is consistent posed to disregard the change in the crumb with avoidance of breaking down of gluten. but to keep the crust reasonably brittle by d) Use of sponge method. holding in an atmosphere with a humidity of e) Use of not too much yeast. about 75 per cent. He has constructed an ap­ f) Proper handling of dough so as to punch paratus to accomplish this.2 It consists of a at optimum time. This favors a uniformly closed chamber in which the cooled fresh small-pored loaf in which hardness and loaves are stored with a ventilating fan to cir­ crumbliness are less conspicuous when they culate the air within the chamber and drive develop. it over the surface of a pan containing a brine g) Loaf should not be overbaked so as not or calcium chloride solution. Its concentra­ to lose too much moisture in the oven. tion is so chosen that it removes water vapor h) Oven should not be too hot, and baking from the air, or adds it, so as to keep the circu­ should be slow rather than fast. lating air at the desired humidity. The device i) Loaf must not lose too much moisture in was employed in an Amsterdam bakery with cooling. success. Bread ten hours old was sold with- j) A thin crust when stale is less con­ spicuous than a thick one. 1 Cf. Platt, op. cit. Other factors in the manufacturing process 2 Depicted in J. R. Katz, "Can We Retard or Pre­ vent the Staling of Bread?" Bakers WeeJdy, Feb. 10, on which there seems to be less general agree­ 1934, LXXXI, 35. ment are: PROLONGING THE LIFE OF BREAD 245

a) Very rapid cooling of loaf is advan­ fermentation, to reduce loss in weight during tageous, if at the same time the loaf is not the first few hours after the baked product permitted to lose too much moisture. comes from the oven, and to affect the re­ b) Slow baking is said by some to be ad­ distribution of moisture as the loaf cools. 2 vantageous, but denied by others. It is said h) Malt extract added to dough is fa­ to hasten staleness especially with slack vorable. doughs. i) Katz3 found that aldehydes and some c) Sour-dough fermentation is said to pro­ alkaline bases prolong the life of the loaf in­ duce a bread that grows stale slowly. On the definitely. However, their use has not been other hand, acidity is said to hasten stale­ found practicable, partly because they are ness,! although sour dough is liable to be more not without physiological effects, partly be­ acid than yeast bread. cause they need to be used in appreciable amounts. The following ingredients seem to affect the life of the loaf: In some of the respects above listed the a) High-quality flour acts favorably, espe­ crust behaves in a manner quite opposite to cially short extractions. The dress seems also crumb. To secure a crust that will remain of influence; very fine grinding is said to be crisp for a long time the following practices unfavorable. should be observed: b) Yeast quality is important. The effects a) High fermentation temperature. of different types of yeast have not yet been b) Much yeast. adequately investigated. Some English bakers c) As little water as possible in dough. believe beer yeast produces bread with longer d) Small amount of salt. life than distillers' yeast. c) Milk is favorable. It may again be pointed out that the several d) Too little salt is said to be unfavorable. effects on crumb of the procedures or ingre­ e) Five to ten per cent of rye flour is said dients above listed have not been established to be slightly favorable. by exact measurement. They are based on f) Gelatinized starch as in scalded flours or inspection. How unreliable such judgments boiled potatoes is favorable. However, accord­ may be has been pointed out by Platt.4 It is ing to Katz, potato starch retrogrades much important that they be .firmly established by faster than wheat starch. such measurement, for which perhaps only mechanical methods to determine the struc­ y) Shortening is favorable - why is un­ known. The writer has suggested that it forms tural strength of crumb by testing instru­ membranes impervious to moisture and car­ ments such as are used by engineers will bonic acid which tend to hold back both in prove reliable. Until this will have been done, it is idle to speculate about the reasons why specific procedures or specific ingredients act I Cf. L. Boutroux, "Sur la fermentation panaire," as they do. For the present, about all one Anrwles de chimie el de Physique, June 1892, Serie VI, XXVI, 145-201. According to E. Fouard, acid tends can say is that: to coagulate starch solutions (Theses presentees it 1. Anything that increases the water con­ la Faculte des Sciences de Paris ... . 1" Tllese.­ Recherches sur ['Mat colloidal de l' Amidon, et sur sa tent seems to be favorable to long life (much e~nstitution physico-chemique. 2' These.-Applica­ high-quality gluten, gelatinized starch, milk, Iron des parois semi-permeables it la delermination high-speed mixing, malt extract). des poids moleculaires (Dissertation, Paris, 1911; Laval, Barneoud, 1911), pp. 78 fT. 2. Anything that hampers the mobility of

2 G. M. Weber and C. L. Alsberg, The American moisture in the cooled loaf perhaps prolongs Veaelable-SllOrtellin(J Industry, Its Ori(Jin and De­ life (shortening, small-pored texture). velopment (Food Research Institute Fats and Oils Studies 5), June 1934, p. 279. 3. Anything that conceals the effects of

3 Het Olldbakken Worden van het Brood in Verband aging of starch prolongs the loaf's life in that met het Vraagstllk van den Nachtarbeid der Bakkers. the loaf remains acceptable to the consumer 1 Op. cit. (thin crust, very brittle crust). 246 THE STALE-BREAD PROBLEM

FOOD VALUE OF FHESH AND OF STALE BHEAD dough mass than small loaves. If for any reason the temperature of the oven is too In former times, it was believed that stale low, or if the time of baking is too short, the bread had greater nutritive value than fresh, interior may remain somewhat doughy and perhaps because it was believed, erroneously, for this reason perhaps not very digestible. to be drier and therefore a more concentrated In such bread, some yeast might easily re­ food per unit of weighU Indeed, the convic­ main alive and lose vigor only after a time, tion existed, and in some quarters persists to so that such bread when fresh might cause the present day, that the consumption of fresh gastric fermentation. Furthermore, When bread may be injurious. It has been claimed chewed, fresh bread of this character might that it causes symptoms of gastric pressure easily form compact boluses which perhaps and even vomiting. Cases are on record in irritate the stomach. Hammonda showed that 2 which it is alleged that death resuIted. In recently baked yeast bread when pressed into view of the insistent demand of today for a compact condition resisted the digestive absolutely fresh bread, one wonders whether power of the stomach much longer. It is there­ in such cases bread had to take the blame fore quite possible that in olden times fresh which really belonged to some other ele­ bread caused untoward effects, and the more ment of the diet or whether the breads of so since per capita consumption was much former times were so different from those of greater then-at least in America-than now. today that the consumption of considerable Jungmann,4 however, compared the beha­ fresh bread did in fact produce feelings of vior of fresh and of stale bread in the mouth malaise and even illness. and toward pepsin-hydrochloric acid without The bread of former times was undoubtedly being able to discover any material difference. different from that of the present. Flour con­ He suggested that, since fresh bread takes less tained more of the bran coat of the wheat chewing to prepare it for swallowing than berry, which is digested with difficulty. The stale, possibly it forms firmer lumps in the nature of fermentation was not understood stomach and therefore calls forth sensations and pure yeasts were unobtainable. Bakers of pressure or even vomiting and gastric used brewers' yeast or saved a piece of dough cramps in persons with a so-called delicate from one batch with which to inoculate the digestion. He was not, however, able to secure next. The fermentation process was therefore experimental evidence in support of his sug­ less well under control. Furthermore, for­ gestion. merly-and in some countries today-it was Lindet,5 on the contrary, states that stale the custom to bake quite large loaves. These bread is less digestible than fresh. This is an require a longer period of baking to permit inference based on the fact that stale bread the heat to penetrate to the center of the contains a somewhat lesser quantity of sol­

1 BoussingauIt, op. cit. uble starch than fresh, since Lindet presented 2 Maurizio, op. cit., p. 362. no experimental data on the digestibility of 3 W. A. Hammond, "Experimental Researches Rel­ bread. Lindet assumes that soluble starch is ative to the Nutritive Value and Physiological Effects more digestible than insoluble and that there­ of Albumen, Starch, and Gum, When Singly and Ex­ clusively Used as Food. Prize Essay," Transactions fore stale bread is less digestible. Roux,6 how­ of tile American Medical Association, 1857, X, 511-87. ever, studied the changes starch undergoes in 4 E. Jungmann, "Studien tiber MehI und Brot," bread to determine whether they are the same Archiv fiir Hygiene, 1895, XXIV, 109-23. 5 L. Lindet, "Sur Ia transformation du pain tendre as those that take place with time in starch en pain rassis," Comptes rendlls hebdomadaires des paste and render it more resistant to such seances de ['Academic des Sciences, Apr. 21, 1902, digestive ferments as diastase and therefore CXXXIV, 908-10. 60p. cit. perhaps less digestible in the gastro-intestinal 7 "Abhandlungen zur physikalischen Cbemie del' tract. He reached the conclusion that the Starke und del' Brotbereitung. XX. Ober den Zusam­ starch in bread does not behave like starch menhang del' Anderung del' Starke beim Altbacken­ werden des Brotes und beim Retrogradieren von paste and that stale bread is no less digestible Starkeklei stcr." than fresh. Katz,7 however, found the starch FOOD VALUE OF FRESH AND OF STALE BREAD 247 of stale bread less easily attacked by malt way to keep consumption down not to serve diastase than that of fresh bread. bread until some time after it had left the Katz,l using the technique of Pawlow, found oven when, because of the beginning onset of that there is no difference in the quantity of staleness, it was less attractive to the taste saliva, gastric juice, or pancreatic juice se­ and therefore less largely eaten. It must be creted by dogs when they are fed fresh and remembered that those were the days when stale bread. However, after salivation and servants, retainers, employees, and appren­ chewing, fresh and stale crumb have quite tices very often received but little in money different consistencies. The stale bread was wages and were lodged, clothed, and fed by then crumbly, but the fresh bread formed a their masters or employers. It was to the in­ heavy lump from which small particles could terest of the employer or lord of the manor to be broken off only with difficulty. Katz sug­ encourage the consumption of cheaper foods gests that herein may lie a basis for the com­ like the coarse grains. monly believed difference in the digestibility At any rate, the belief that the serving of of fresh and of stale bread. stale bread tends to reduce consumption was One is tempted to infer that the attitude in held during the World War. As has been former times may really have been a rationali­ pointed out above, in many countries threat­ zation in response to the generally low level ened with a shortage of the wheat supply, of the standard of living. Fresh bread, be­ regulations were passed prohibiting the sale cause attractive in flavor and in texture to of bread until a certain number of hours after most persons, is consumed in greater amount leaving the oven. Under the conditions of the than stale bread. Perhaps it seemed a good present, there seem to be no scientific data on record demonstrati!lg any material differ­

1 "Gelatinization and Retrogradation of Starch in ence in the food value or wholesomeness of the Bread Staling Pl-ocess." fresh and of stale bread.

This study is the work of Carl L. Alsberg WHEAT STUDIES of the FOOD RESEARCH INSTITUTE

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RECENT CONTRIBUTIONS FROM THE FOOD RESEARCH INSTITUTE (Numbered reprints available free on request) E 45. "The Bitter Glucoside of the Olive," W. V. Cruess and C. L. Alsberg. Journal of the American Chemical Society, October 1934 G 69. "Observations on Wheat Consumption," Carl L. Alsberg. Proceedings of the Fifth Pacific Sci­ ence Congress, Victoria and Vancouver, Canada, June-July, 1933 G 70. "What about Wheat Prices?" Holbrook Working. Proceedings of the Fifth Pacific Science Con­ gress, Victoria and Vancouver, Canada, June-July, 1933 G 71. "British Wheat Yield per Acre for Seven Centuries," M. K. Bennett. Economic History (Sup­ plement), February 1935 G 72. "AAA as a Force in Recovery," Joseph S. Davis. JOllrnal of Farm Economics, February 1935 G 73. "Planned Agricultural Adjustment in the United States, 1933-34," Joseph S. Davis. Chapter i in Commodity Control in the Pacific Area, edited by W. L. Holland (London, Allen and UnWin, 1935) G 74. "Differential Price Behavior as a Subject fo r Commodity Price Analysis," Holbrook Working. Econometrica, October 1935 G 75. "Agricultural Fundamentalism," Joseph S. Davis. In Economics, SocioloYII « the Modern World, edited by Norman E. Hines (Cambr idge, Harvard University Press, 1935) FOOD RESEARCH INSTITUTE STANFORD UNIVERSITY, CALIFORNIA

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