Production of

Mushroom The technique ofl'ers the possibility of greatly cutting the cost of a mushroom- flavored food material, although the physical form and texture usually as- Mycelium sociated wdth mushrooms must be sacrificed. Harry H urn ¡eld The principles of the method are based on the fact that when a liquid that contains the required chemicals and food supply is continuously stirred vigorously at the right temperature and Growing mushrooms has become an mixed thoroughly with a constant sup- important industry in the United ply of air, many micro-organisms re- States. Of the estimated annual pro- producía in it with great rapidity. The duction of 62 milHon pounds, 20 mil- method is used commercially in the lion reach the consumer as fresh mush- production of baker's yeast and feed rooms, 18 million in cans, and 24 mil- yeast. More recently it has been applied lion as flavoring in soups. to the large-scale production of anti- Consumption might be even greater biotics, such as penicillin and strep- if production costs could be reduced. tomycin, as well as to the manufacture With the trend towards packaging pre- of citric and gluconic acids. })ared, ready-to-serve food products, The mycelium proved to be not too the use of mushroom flavor in a num- particular about the medium on which ber of such preparations doubtlessly it will grow, but it does have certain will increase. The problem is to incor- requirements. It seems now that a porate mushroom flavor without mark- good commercial product can be grown edly increasing the cost of the product. on any medium that contains a suit- The mushrooms in the retail mar- able sugar and other essential nutrients, kets are really the fruits of a plant that that does not contain an ingredient in- grows as a mat of fine strands or hibitory or toxic to the growth of the threads on the organic material in the mycelium, and that does not impart a soil or in a mushroom bed. When con- characteristic flavor of its own during ditions of temperature, moisture, and its use as a medium. food supply are right, such a mat, or mycelium, periodically forms mush- To OBTAIN PURE-CULTURE UlUsh- room fruits near the surface of the soil. room mycelium, \Wí: either germinated These are the familiar buttons and mushroom spon^s or made tissue cul- caps. Soon after they push up through tures of various parts of the mushroom. the bed they are ready for harvest. Then we grew the mycelium on an Although people over the w^orld cat agar medium in order to maintain the mushrooms of several species, in the pure cultures. The cultures may be in- United States only one species—Aga- oculated into sterilized compost, grain, ricus campestris—is grown commer- or tobacco stems, and allowed to grow cially. to provide the material known in the In 1947, I discovered that the vege- trade as mushroom spawn. The spawn, tative, or underground, part (myce- w^hen planted in mushroom beds, pro- lium) of that species will grow under duces the mushrooms sold commer- conditions of submerged propagation. cially. 242 PRODUCTION OF MUSHROOM MYCELIUM 243 For the submerged propagation of stag(i. That is, we have grown all three the mycelium, the procedure now in strains in 40-gallon batches in our use consists in transferring some of the pilot-plant fermentor. Each batch has mycelium grown on agar in a test tube produced 35 to 38 pounds of mycelial to 50 milliliters of sterile liquid me- cake with good mushroom flavor. dium in a 250-milliliter Erlenmeyer In both the Fernbach and the larger (conical) flask. The flasks are shaken fermentors, a rate of air flow of 1 liter on a machine in a room at 77° F. until of air a minute per liter of culture a heavy growth of mycelium has de- medium gives rapid growth. Lower veloped. The time usually required is rates give slower growth. Higher rates 5 to 6 days. This inoculum is then trans- do not materially increase the growth ferred to 2 liters of medium in fer- rate. mentors made from Fernbach (spheri- We harvest when good growth and cal ) flasks and incubated to maximum good mushroom flavor have been pro- growth. This culture suspension is used duced in the large fermentors by taking as inoculum in the larger fermentors out half to three-fourths of the culture with a culture-medium capacity of 16 and adding an equal volume of fresh to 20 liters. sterile culture medium. In this man- It has been necessary to consider var- ner a number of consecutive harvests iations in so-called strains of Agaricus are obtained without contamination of campestris. Plant species, like animal the culture medium. species, have familylike variations. Immediately after harvesting, we Therefore I have isolated and tested separate the mycelium from the culture more than 40 cultures of strains of liquid by centrifuging. Then we re- Agaricus campestris. suspend the mycelium cake in water Among them I have found three that and again centrifuge. are well able to adapt themselves to \¥e pack the mycelium into suitable growth in an agitated, aerated liquid cans and seal and sterilize the filled medium. Each has characteristic mush- cans at 15 pounds of steam pressure room flavor. Each can be distinguished for 20 minutes. In some cases we have from the others by a characteristic dif- frozen it and stored it in a freezer until ference in flavor. Two of the strains used. Drying the mycelium, either by were isolated from mushrooms of the lyophilizing (drying under vacuum white variety and one from the cream from the frozen state) or on a drum or brown variety of Agaricus cam- drier, has been tried, with some loss of pestris. All have certain characteristics flavor in both cases. in common. They grow more rapidly We have obtained good yields on than the other isolations. The hyphac, media composed of juices pressed from or mycelial threads, are more slender. various fruit and vegetable wastes, They produce an abundance of so- such as asparagus butts and pear waste. called secondary spores in the liquid Our more recent investigations show medium. The secondary spores were that a desirable product is obtainable first described by Albert Kligman in from media made from pear waste, a 1932 at Pennsylvania State College. rice-bran extract, or beet molasses, and He found them in old cultures on also from a synthetic medium contain- solidified (agar) medium. From obser- ing dextrose and inorganic salts. Media vations up to the present time, it seems containing asparagus juice or alfalfa likely that the ability to produce the juice seemed to impart the flavor of secondary spores may account for the those constituents and were deemed ability of the strains to adapt them- less desirable. selves to submerged growth in a liquid Basic studies in progress in 1949 medium. demonstrated that the essential nutri- The process also has been carried ent requirements for the growth of the successfully through a semipilot-plant mycelium of A. cam.pestris are com- 244 1950-19 5 1 YEARBOOK OF AGRICULTURE paratively simple. Sources of nitrogen sition of the medium on the develop- utilized include ammonia^ urea^ pep- ment of the intensity of the mushroom tone, monosodium glutamate, a mix- flavor. ture of amino acids, and probably a Our tests on the possibilities of number of other nitrogen compounds. spawning mushroom beds by spraying Most of the sugars tested, which in- the liquid culture on the compost gave cluded hcxoscs, pentose^s, and disac- negative results. The mycelium grows charides. give good growth. The poly- very rapidly, forming a white mat over saccharides (soluble starch and dex- the surface of the compost bed over- trin) also arc suitable sources. How- night, and then disappears nearly as ever, a form of soluble cellulose (sodi- quickly. The hyphae apparently are um carboxymcthyl cellulose) cannot unable to penetrate into the compost be fermented. Apparently a wide range or arc unable to compete wdth the of carbohydrates can serve as sources other micro-organisms present. This of energy for growth of mycelium of method of seeding beds of compost, if A. campestris. successful, would help reduce the costs We have determined approximate of the commercial grower who sup- optimum concentrations for the vari- plies the commercial trade with mush- ous elements rccjuired and have devel- room fruit caps. oped a basal medium which contains We have grow'n these cultures in our the required amounts of sugar, nitro- laboratory on rye grain by the method gen, phosphorus, potassium, mag- used in making commercial grain nesium, sulfur, calcium, and the trace spawn. When w^e used grain spawn to elements, iron, manganese, zinc, and start beds in the customary commercial copper. manner, the hyphae formed an excel- The development of this synthetic lent fluffy growth on the grain, but medium of know composition and the again were unable to grow and spread determination of the nutrient require- into the compost. It may well be that ments and utilization of various nitro- these strains are spontaneous mutants, gen and energy sources aid in investi- which can reproduce themselves only gations on the suitability of various vegetatively in pure culture medium. media made from fruit and vegetable Results of analyses of mushroom wastes. If the composition of the press mycelium produced by submerged fer- juice of a particular waste material is mentation show a protein content (ni- known, a preliminary forecast can be trogen X 6.25) of 49.1 percent, fat 3.1 made on the suitability of the w^astc as percent, and mineral constituents, as a source of substrate for mushroom ash, 8.1 percent, calculated on a mois- mycelium production. ture-free basis. The mycelium of the During the continuous-fermentation white variety contained, in micro- tests in the Fernbach and in the larger grams per gram of dry mycelium, the (20-liter) fermentors, successive har- following vitamins: Thiamine, 8,7; vests were made as soon as enough riboflavin, 47; niacin, 190. For the mycelium had been produced to give a cream variety, the figures were 8.7, good yield. We discovered that when 90, and 290, respectively. Both showed this procedure w^as followed, much of only a trace of ascorbic acid. The re- the characteristic mushroom flavor w^as sults compare favorably with those for lost. To assure the production of a commercially grown mushrooms. good-flavored mycelium, it w^as found The centrifuged mushroom myce- necessary to grow each stage of de- lium looks like a fresh yeast cake and velopment of the culture until a full contains about 25 percent solids, as mushroom flavor had developed. compared with 10 to 12 percent solids We arc investigating the effects of in fresh mushrooms. The mycelium rates of aeration, agitation, length of should be suitable for use in soups, time of fermentation, and the compo- gravies, and condiments, w^herever it PRODUCTION OF MUSHROOM MYCELIUM 245 is not essential that recognizable pieces possibilities for the development of of mushroom be present. It is likely, of palatable food materials. Other species course^ that people will continue to might be suitable as sources of feeds of want whole mushrooms, even though high nutritive value or for the produc- the mycclial cake may be made for tion of enzymes, antibiotics, toxins, and flavoring. other organic compounds. The advantage of mushroom myce- Another direction that research lium over fresh mushroonis would seem might take is toward basic factors in to be largely that of more economical the medium that might enhance or production, although the assurance; of otherwise modify and improve the con- a constant and reliable supply might centration and quality of the flavor. also be an important factor. Flavor substances are very important After the production of the my- commercially. They are complex celium of A. campesiris has been car- chemically and constitute an important ried through the pilot-plant stage, the and interesting field for the agricul- use of mycelium of other mushroom tural chemist and microbiologist. species known to have dc^sirable flavor characteristics remains to be ex- HARRY HUMFELD, a microbiologist plored. The mushrooms of many edible at the Wester?! Regional Research Lab- species are now available only in lim- oratorjj has been engaged in research ited quantities and only for short in microbiology in the Department periods during the year. A reliable and since 1927. He is a native of Holland constant source of supply of mycelium and has degrees from Oregon State of desirable species would seem to offer College and Iowa State College.

CITRUS MOLASSES is no good with hot biscuits, but to Florida cattle it's ice cream and cake. On the big ranches of central Florida, cattle greedily slurp up the black, sticky molasses as it trickles from 1,000-gallon drums into feeding troughs, or they chew their bulky feeds with more gusto if the molasses has been poured over them to make a sort of hay à la mode. This use of citrus molasses is an answer to one waste-disposal problem. About 60 percent of Florida's huge citrus crop was processed in 1950, and the refuse from the processing plants created a serious disposal problem. Citrus molasses has (^ased the problem somewhat. Florida cattlemen, scientists, and processors joined in the effort to turn the waste into livestock feed. Scientists found that it could be converted into citrus pulp and a brownish-black sirup, which they called citrus molasses. The University of Florida ran trials on the value of the two products as cattle feed. The results were satisfactory. The Florida Agricultural Experi- ment Station found that citrus feeds can contribute to thickness of flesh, glossiness of coat, and flow of milk, and add to general body tone of cattle. Florida pro- duced about 180,000 tons of citrus pulp and 80,000 tons of citrus molasses in 1950. Most of the pulp went to dairy cattle; most of the molasses to beef cattle. The supply and demand are expanding rapidly.—Fred P. Lawrence, Agricul- tural Extension Service, University of Florida, 246 1950-1951 YEARBOOK OF AGRICULTURE Commercial production of Fruit in the United States, 1940-49 average Proportion Average of total Fruit production fruit crop Major areas of production lyOOO tons Percent Oranges and tangerines 3}7co 11 Central Fla., southern Calif. Grapes 2,800 17 Calif., Great Lakes region. Apples 2j6co 16 Central Wash., Shenandoah Valley, upper N. Y., southwest Mich. Grapefruit 2,coo 12 Central Lia., Rio Grande Valley. Peaches 1,500 9 Central Calif., Ga., southwest Mich. xMelons (including cantaloups). . . ï>3CO 8 Calif., Ga., Fla., Tex., S. C, Ind. Pears 750 4 Central Calif., Pacific Northwest. Plums (including prunes) 670 4 Do. Lemons 510 3 Southern Calif. xApricots 220 I Central Calif. Cherries 190 i Western IVtich., western N. Y., central Calif. Strawberries 160 i Southern States, Mich., Pacific Coast States, Mass. Others ^ 270 2 Calif., Fla., Mass., Wash.

Total 16,670 ICC ^ Avocados, hush berries, cranberries, dates, figs, limes, ol'ves, persimmons, pineapples, and pomegranates.

The four main types of fruit processing in the United States^ 1940-49 average Propor- tion of Â'cera^e quantity— total " Fruit crop Canned Dried Frozen Crushed ^ Major processing areas processed jfioo i-poo I poo I poo Percent tons tons tons tons Oranges. 26 950 Fla. Grapes. . 79 20 I,030 1,150 Calif. Apples. . 26 220 130 27 300 X. Y., Shenandoah Valley, central Wash., Calif. Grapefruit 51 89 920 Rio Grande Valley, 1^'la. Peaches 40 480 130 Calif. Pears ; 38 260 18 5 Calif., Pacific Northwest. Plums (including prunes). 73 30 450 3 Calif. Lemons 32 160 Do. Apricots 71 64 83 Do. Cherries 52 3C 2 N. Y., Mich., Wis., Pacific Northwest. Strawberries. 32 I Pacific Northwest, Southern States. Others 2 72 62 93 31 10 Calif., Fla., Mass.

Total 41 1,291 1,934 158 3,501 ^ Includes fruit used for making juices and for fermented products, brined (in the case of cherries) and some quantities used for preserves, jams, and jellies. 2 Avocados, bush berries, cranberries, dates, figs, limes, olives, persimmons, pineapples, and pomegranates. Prepared from U. S. Bureau of Agricultural Economics data.