Concentrated

and Dried thai left from the separation of for and , also goes into manufactured milk products. The fluid milk (equivalent utilized in the Milk production of the concentrated and dried is about 2vO billion pounds. B. H. Webb Approximately 6/2 billion pounds of milk is made into each year, and 280 million pounds is canned as sweetened , both largely for household use. The ice- The concentrated and dried milks cream industry uses a]:)out 3 billion are manufactured to conserve fluid ]:>ounds of skim-milk concentrates to milk for use where fresh milk is scarce build up the nonfat milk solids of ice and during seasons of low production. cream. The manufacture of foods other Specialized knowledge and equipment than products requires prepa- enable processors to manufacture the ration of milk concentrates from 4 bil- difièrent concentrated milks by remiov- lion pounds of milk. About one-third of ing part of the water from the milk. the production of concentrated and The products are the source of concen- dried milks is used in beverage milks, trated milk soUds needed for the prep- cottage and other special , malt- aration of many foods, both in the ed milk, and animal feeds. home and in the food factory. The names assigned by custom to the SWEETENED CONDENSED MILK is concentrated milks have confused the manufactured by a few simple but vital layman and provoked the etymologist. operations. Harmful bacteria and en- Plain condensed whole and skim milks zymes are destroyed by fore warming. contain no and are perishable In that treatment, the milk is heated to products. Sweetened condensed whole about 185° F., which helps also to and skim milks are preserved by the control thickening of the finished milk addition of sugar. Evaporated milk is during storage. The hot milk is drawn not sweetened; it is sterilized in cans. into the vacuum pan—in which milk Dried milks may be either dried whole boils at temperatures as low as 100° F. or dried skim milk^ except that Con- and water is rapidly removed without gress in 1944 amended the Food, Drug, coloring the milk or giving it a cooked and Cosmetic Act by providing a stat- flavor—together with 18 pounds of utory definition for dried skim milk sugar for each 100 pounds of milk, A under the names "nonfat dry milk sirupy milk, which tastes delicious, is solids" and "defatted milk solids." drawn from the vacuum pan and Nearly half of the 120 billion pounds cooled with continuous agitation. Tiny of milk produced annually in the crystals of lactose (milk sugar) grow is consumed as market spontaneously when the condensed milk and cream. From the remainder milk is stirred at about 85°. Improper (except the milk used on the farm), cooling causes the growth of large, such dairy products as butter, , coarse crystals that make the milk taste , concentrated milk, and sandy. Sweetened condensed milk is dried milk are manufactured. Fifteen packed in cans or barrels. When held billion pounds of skim milk, part of at 70° for 6 or 8 months, the product

690 CONCENTRATED AND DRIED MILK 691 darkens and thickens. The change can and the persistence of good viscosity be greatly retarded by storing it beiow and body characteristics during stor- 60°. Sweetened condensed milk retains age if the solids content were raised to its acceptable condition for at least a 28 percent. year if held at a low temperature. It is Small crystalline particles, about the not damaged at temperatures well be- size of the head of a pin, sometimes low 0° F. because of its high sugar appear in stored evaporated milk. They content. are complex milk salts that have crys- Perishable concentrates, produced tallized and settled to the bottom of the and packaged in bulk for food proc- can. The conditions governing their essors, are called plain condensed milk. separation are little understood ; hence They contain no sugar and must be their formation cannot always be pre- held under refrigeration. The manu- vented. Salt crystals in evaporated milk facturing process consists simply in are not harmful, but sometimes they heating, condensing, and cooling the are an annoyance, especially when they milk. obstruct the holes in nijDpk^.s of babies' bottles. EVAPORATED MILK, unlike sweetened Bureau of Dairy Industry chemists condensed milk, contains no added have studied evaporated-milk salt crys- sugar. Spoilage is prevented by sterili- tals. The crystals are composed largely zation with heat. Steps in the manufac- of calcium citrate, with traces of phos- ture of evaporated milk arc: Fore- phates. Crystals generally do not begin warming, evaporation, homogeniza- to appear in the milk until it has been tion, standardization, , and in storage 6 months or more. They sterilization. grow more rapidly when the evapo- The time and temperature of fore- rated milk is held at room temperature warming affect the stability of the milk than when it is stored at 60° or below. toward heat and the viscosity, or body, The formation of crystals can be ac- developed in it during sterilization. celerated by adding calcium chloride Forewarming is generallv done at a and sodium citrate or by lightly seed- temperature of 190° to 212° F., de- ing the milk with calcium citrat(\ pending on the condition of the milk. Early in the Second World War the Dairy scientists recently investigated Governrnent had to store much evapo- the effect of forewarming milk to tem- rated milk. Some of it, after being held peratures up to 300° on its heat sta- for 2 or 3 years, showed citrate crystals, bility and viscosity. They found that a thinning in body, and some separa- milk fore warmed at 250° for 3 to 4 tion of fat and protein. Dairy scientists minutes attained a much greater heat knew that evaporated milk was a re- stability than when temperatures below markably stable product; they deter- boiling were used. The discovery en- mined nevertheless to find a way to ables manufacturers to raise the solids increase that stability. They found that content of evaporated milk without en- the magnitude of the storage change countering coagulation difficulties dur- depended partly on the temperature. ing sterilization. Evaporated milks have Below 60° F. changes were slight, but been made with a solids content up to above 90° the product deteriorated 38 percent. noticeably in a few months. It was Storage t(^sts on milks containing found advisable to hold evaporated various percentages of solids, however, milk at a temperature not to exceed have shown that the best milk is pro- 75° and to turn the cases every 6 weeks duced when the solids are held within to retard fat separation. the limits of 26 percent to 32 percent. Fat separation in evaporated milk The present evaporated milk with a depends not only on the efficiency of solids content of 26 percent would be homogenization, on viscosity, and on improved in terms of nutritive value conditions of storage, but also on the 6^2 1950-1951 YEARBOOK OF AGRICULTURE Approximate composition, degree of concentration, and density of mille and concentrated milks

Milk Degree of solids Pro- Milk Su' concen- Density Product Water not fat Fat tein sugar Jsh crose tration at 60" F. Per- Per- Per- Per- Per- Per- Per- Specific cent cent cent cent cent cent cent Ratio gravity Milk 87.0 9.1 3.9 3'S 4.9 0.7 1.032 Skim milk 90. 5 9.4 .1 3-5 5.1 1.035 Evaporated milk 73 «7 18.4 7.9 7.0 9.9 1.5 2.02:1 1.066 Plain condensed whole milk. . . 64.0 25.2 10.8 9.7 13.6 1.9 2.77:1 1.095 Plain condensed skim milk . . . 70.0 29.7 •3 II. I 16.1 2.5 3.15:1 1.125 Sweetened condensed whole milk 28.0 8.5 7.7 10.7 1.6 43.5 2.20:1 1.266 Sweetened condensed skim milk 28.0 29.7 .3 16.1 2.5 42.0 3-15:1 1.366 Dried whole milk 3.5 69.8 25.8 38.0 6.0 7-5o:i .550 Dried skim milk 2>-í 95.5 I.o 3S'(> 52.0 7.9 ...... 10.20:1 ,600 physical state of the protein that is as- civilian use, although canned sociated with the fat in the cream milk is available in some markets. layer. Easily dispersed fat layers are less objectionable than layers that are DRIED MILK w^as one of the chief con- held tightly together by adsorbed, tributions of the dairy industry to win- partly denatured protein. Causes for ning the Second World War. Before the gradual changes in the milk pro- the war the production was largely tein during storage of evaporated milk dried skim milk and dried , are still being investigated. both byproducts. During the war a A new canned that is great demand for dried whole milk high in energy value and suitable for prompted a sevenfold increase in its drinking directly from the container manufacture. The dried milks are now was developed by scientists in Govern- made by three principal methods, usu- ment and industry in response to re- ally designated as spray, atmospheric- quests by the Army Quartermaster drum, and vacuum-drum processes. Corps. The milk was wanted for use In the spray process, partly concen- on invasion beachheads, where the trated milk is sprayed by pressure or landing forces frequently needed centrifugal means into a chamber quickly available nourishment. The through which a current of heated air milk, a sterile product in sealed con- is directed. The shape of the drying tainers, has excellent storage life. It chamber may be conical or rectangu- contains approximately 20 percent lar, and its size is proportioned to the total solids; ordinary fluid milk con- spray and the amount and direction of tains about 13 percent. The extra the flow of air used. The fine droplets solids consist of , flavoring ma- of milk dry almost instantaneously to terials, and added milk solids from fine particles of powder, which are re- concentrated milk. The many flavors moved from the air by gravity and the tested in developing the formulas in- cyclonic motion of the air, and, in some cluded fruits, honey, maple, chocolate, cases, with the aid of an air-filtering and . Chocolate and caramel device. Dried milks made by this meth- gave a product of satisfactory flavor od are finely divided, very soluble, and and small batches of both were made hygroscopic. commercially for the Quartermaster Although unconcentrated milk can Corps. These flavored milks have not be dried by this method, partly concen- been extensively manufactured for trated milk is preferred for economy CONCENTRATED AND DRIED MILK 693 and the effect on certain properties of Because of the high drum tempera- the dried product. The milk usually is ture necessary for drying the film, there concentrated in a vacuum pan or a is a slight discoloration of the product continuous evaporator. The concen- and a partial coagulation of the pro- tration, which varies with the type of teins that makes them insoluble. Driers spray and the drier used^ may be as of this type are used mainly in drying great as 44 percent solids. Dried milks skim milk and buttermilk. The dried made from concentrated milks have milk thus made does not absorb water particles of larger sizes than those as readily as powder dried by the spray made from unconcentrated milks and process. can be reconstituted more readily. The The vacuum-drum process is essen- dried-milk products also retain less gas tially a roller process. The rolls, or when subjected to vacuum in pack- drums, are enclosed in a chamber that aging. is kept under partial vacuum during Dried skim milks are usually made the drying operation, thus making it from skim milks that have been pre- possible to dry milks at temperatures heated to at least 185° F. for varying below their boiling points. The ]orod- periods, because it has been found that ucts obtained by this process resemble the dried product made from milk those made by the spray process in solu- treated in this way has better baking bihty, color, flavor, and hygroscopicity. qualities than products made from Great quantities of dried milk were milks that have received only a pas- used to feed the Allied armies. Scien- teurization treatment. tists and technicians were called upon In manufacturing dried whole milk, to solve the problems of packaging and the milk must be heatc^d suihciently to keeping quality which arose when the destroy the fat-splitting enzymes^ li- milk was subjected to the rigors of war- pases. The temperature and the time time storage and shipping. of heating needed to destroy the lipases The spray-dried and vacuum-drum- have not been estabhshed definitely. dried milks have a great avidity for However, temperatures of 175° to moisture and must be packaged so that 180° F. for 30 minutes have been used they are guarded against absorption of successfully in the manufacture of moisture from the atmosphere. Dried dried whole milk. The temperature of skim milk is usually packed in slack the air to be used in drying varies with barrels of 200-pound capacity with the make of the drier. It may be from moistureproof double liners, or in mois- 240° to 320°, depending on the effi- tureproof bags of 100-pound capacity. ciency of the spray, the rate of feed, For Army export the 25- and 50-pound the degree of concentration of the milk hc;rmetically sealed round or square used, and other factors. In the manu- base-metal cans were the most satis- facture of this product, it is also im- factory. Metal drums and moisture- portant to keep the milk from com- proof fiber drums have also been used ing in contact with exposed copper or for export. iron. Extremely small quantities of cop- Dried whole milk deteriorates rela- ]:)er, especially, will accelerates markedly tively rapidly when packaged in con- the deterioration of the fat. tact with air. To retard or prevent In the atmospheric-drum process, spoilage through oxidation of the fat, steam-heated revolving single or double the product is packed in tin containers drums are coated with a film of partly of from 1- to 50-pound capacity and concentrated milk, which dries and is the air is removed as completely as pos- scraped off by close-fitting knives after sible by evacuation and replaced by an a partial revolution has been com- in(Tt gas, usually nitrogen. pleted. The product is then ground to Many flavors may develop during a powder and packed in barrels or the production and storage of dried sacks. milks. For the most part, they can be 694 1950-1951 YEARBOOK OF AGRICULTURE controlled through the use of advanced process for sterilizing fluid concen- methods of manufacture and pack- trated milks affords a great opportunity aging. Aside from the off-flavors that for increasing their utilization. The may be inherent in milk, the principal production of sterile packaged milks of types of off'-flavor likely to be found normal flavor and color and with good in dried milks are "cooked" flavors, chemical and physical stability may which are developed during manufac- some day be possible. Means for accom- ture, and staleness, rancidity, and tal- plishing this include sterilization by lowiness, which may develop during dielectric heating, cathode rays, ultra- storage. sonics, and antibiotics, or by improved Some basic rules for the manufac- high-temperature, short-time heating. ture of spray-dried whole milk of good How effective any one of these methods keeping quality have been developed may become in providing the consumer by research workers : with an acceptable concentrated bever- Milk of low bacterial count should age milk is unpredictable. Most scien- be dried as soon after it is drawn from tists still believe that heat is the surest the cow as practicable. and safest sterilizing agent. Evaporated The milk must not come in contact milk has already been quickly heat- with copper and iron; stainless-steel sterilized by two experimental methods equipment is best. that give products of generally accept- The must receive a heat able, though slightly cooked, flavor. treatment of 175° for 30 minutes, or By one method, cans of milk are steri- its equivalent in time and temperature lized under severe agitation in less than of heating, for lipase destruction. 4 minutes at 260° F. By the other The moisture content of the powder method, the milk is sterilized at 280° should be below 2.5 percent. by rapid passage through a special Dried whole milk should be gas- tubular heater, and then aseptically packed in tin cans so that the oxygen packaged. Both methods produce thin content of the atmosphere of the con- evaporated milk, which lacks long tainer does not exceed 2 percent. storage stability. The fat and protein The temperature of storage should separation of such milks during storage be less than 75° F. must be overcome before these prod- If these conditions are fulfilled, and ucts can be offered to the public with reasonable care is exercised in the complete assurance that the contents manufacturing operations, the dried will keep until the can is opened. milk will remain in good condition for Utilization of dried milks will be 6 months to 1 year. broadened as scientists gradually learn Dried skim milk should contain less how to extend the time that a fresh than 3.5 percent moisture. Powders of flavor can be retained. There is need, more than 5 percent moisture held at too, for improvement in the physical high storage temperatures deteriorate properties of the powder particle. If very rapidly in color, flavor, and dried milk could be made so that it solubility. would disperse and dissolve in water as readily as sugar, its popularity with FURTHER UTILIZATION OF MILK in consumers would increase. the concentrated and dried form will come as improvements are made in B..H. WEBB is a principal dairy man- these products through advanced ufacturing technologist in the Bureau methods of processing. Chemists, bac- of Dairy Industry. He received the teriologists, dairy technologists, and 1943 Award in Dairy Manu- engineers are constantly engaged on facturing fiom the American Dairy the problems of heating, concentrating, Science Association and the Superior and drying milk. Service Award from the Department The development of an improved of Agricuture in 1948.