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Vol. 22, No. 11
Fermentations in the Food Industries’ F. C. Blanck FOODRESEARCH DIVISION,CHEMICAL AND TECHNOLOGICAL RESEARCH, BUREAUOF CHEXISTRY AND SOILS,WASHINGTON, D. C.
UR American food in-
A survey has been made of o u r present knowledge of often u n s a t i s f a c t o r y . On dustry, according to t h e fermentation processes involved in t h e preparation the other hand, more prothe 1927 Census of of such foods as bread, tea, coffee and Cocoa, sauernouncedflavor is produced in Manufactures, had in that kraut, pickles, vinegar, sauces, olives, cheeses, etc. bread by the latter process. year a total production value Mention should be made of of more than 11 billion dollars. This vast total brought the salt-rising bread, a product of lactic (not yeast) fermentation. food industry into first place among the Smerican manufactur- The products of fermentation here are not carbon dioxide and ing industries. Surprising as this statement may seem, we all alcohol in practically equal amounts, but one third hydrogen appreciate the magnitude of the problem of feeding 120 million and two-thirds carbon dioxide. Salt-rising bread has a finer people, especially when we consider the varieties of foods grain and a more pronounced flavor than yeast bread. and the proverbial appetite of the American people. Tea, Coffee, and Cocoa It is interesting to note the important part which fermentation plays in the process of preparing foods for consumption. Tea, coffee, and cocoa or chocolate are not usually conSuch foods as bread, certain cheeses, cocoa and chocolate, sidered as fermented beverages, but fermentation has its certain cured meats and fish, sauerkraut, pickles, vinegar, part in their preparation. and olives have fermentation as an essential part of their Fermentation in the manufacture of black tea (10) and manufacturing processes. This discussion will be restricted the more recently introduced cassina beverages is produced to the general principles involved in the fermentation of some by oxidizing enzymes. Artificial aging of green coffee (32) of these food products. has been attempted by a number of methods, which have been patented in this and other countries. Probably the Bread-Making most important, both from the research and the commercial Bread-making ( 2 , 3, 5, 12, 14, 15, 20, 31, 34), one of the point of view, is the Robeson patent (26) in which the carelargest food industries of the country, is dependent upon fully washed green coffee is inoculated with cultures of mold fermentation. Including both commercial and home baking, organisms secured originally from a coffee of distinctive approximately 20 billion loaves of bread are annually made character, and incubated under carefully controlled condiwith yeast. The commercial value of bread and related tions of time, temperature, and humidity (26). By this means products for 1927, according to the 1927 census, was $694,- “A green Java or a Brazilian Santos can be transformed in 10 days from a characteristic high-grade rough coffee to a smooth, 000,000. Panary fermentation is essentially an alcoholic fermenta- creamy, Java-like coffee. This method produces a much tion similar to that of beer manufacture, except that in more uniform product, and one having a more desirable bread-making carbon dioxide plays a more important role flavor.”‘ The cocoa and chocolate produced in the United States in than alcohol. As made by the baker, bread is composed of flour, water, salt, sugar, shortening, mineral food, and yeast. 1927 had a total value of approximately $122,700,000. The Yeast, which is the active principle in bread-making, contains fruit of the cacao tree is a large, pear-shaped pod, containing various essential enzymes-diastase, invertase, maltase, pep- from 25 to 40 seeds which resemble a lima bean in size and tase, zymase, etc. For the proper growth and reproduction shape. The pods are split open and the seeds, surrounded by of the yeast, which is responsible for panary fermentation, a sweet, mucilaginous pulp, are fermented in vats which range certain foods are necessary-fermentable sugars, soluble pro- from shallow holes in the ground, lined and covered with tein, and mineral salts. The water used in dough acts as a plantain leaves, to well-constructed wooden boxes in which vehicle for these soluble food materials. Profound changes the beans are raked and turned a t regular intervals. Studies take place in the dough from the time it is mixed until it is of the fermenting beans (29) have been made a t various tropiready for baking into bread. Liquefying enzymes, diastase, cal experiment stations. Knapp (16) has given us a r6sum6 maltase, and invertase-all play a role in converting the avail- of previous work with comments on his own experiments. able raw carbohydrate material of the dough mass into solu- Whymper (33) sums up the present status thus: ble fermentable sugars, which are changed by the zymase The results of fermentation seem to be a little doubtful, though into approximately equal parts of carbon dioxide and alcohol. the practical benefits attained are the conversion of the white or The carbon dioxide generated expands the dough, which red color of the bean into a purplish hue, the hardening of the forms, when baked, a light, porous, finely vesiculated crumb, shells, the loosening of the shell from the endosperm, the “plumping up” of the bean, and the modification and improvement of characteristic of a well-baked loaf-a product practically 100 the odour and flavor. Examination and analysis show that, per cent digestible. Carbon dioxide further hastens the during the alcoholic fermentation of the sugars of the pulp, ripening or maturing of the dough by altering its H-ion con- hydrolysis of some of the bitter and astringent matters of the centration, which in turn, according to Kent Jones, affects bean takes place; a t the same time a certain amount of mineral matter, chiefly potash and phosphoric acid, is remov:‘d in the the colloidal state of the gluten and its physical propertiesliquid diffusing from the fermenting bean (J. H. Hart, Cacao,” elasticity, toughness, spring, etc. Other products formed in 1911; H. Hamel-Smith, “The Fermentation of Cacao,” 1913; relatively small amounts during fermentation impart flavor Knapp, “The Practice of Cacao Fermentation,” 1914). The to the loaf. Comparatively little is really known, however, fermented beans are then dried in the sun or by artificial heat, when they are ready for exportation. regarding the process and the products of panary fermentation. I n general, bread of uniform quality is made by the Sauerkraut use of yeast, whereas the use of sour dough is uncertain and Sauerkraut (19, 25, 24, 25) and its by-product, sauer1 Received October 8, 1930. Contribution No. 95 from Food Research kraut juice, are food products which have attained a high Division.
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degree of popularity in recent years. I n this case the fermentation is brought about by organisms which are normally widespread and require no inoculation. These organisms are salt-tolerant. The salt added not only improves the flavor but, more important, prevents malfermentations. The reducing sugars normally present in the cabbage are broken down into lactic acid with small amounts of alcohol and acetic acid. Studies by Fred and Peterson and their eo-workers have shown that the gaseous product of this fermentation is nearly 100 per cent carbon dioxide, with possible traces of hydrogen and methane. They also showed that the quality of sauerkraut depended largely on the temperature at which the fermentation was conducted. The most favorable temperature was between 60" and 65" F. High temperatures favored the production of soft and pink sauerkraut. A rise in temperature of 3 to 5 degrees during the first 8 days was coincident with the greatest activity of the bacteria and is believed to have been caused by bacterial action. Sauerkraut fermentation is carried out in the absence of air. The oxygen and necessary energy are obtained from the constituents, mostly sugars, extracted by the salt. The active organisms do not utilize the lactic acid formed, so the fermentation ends with the acid production. Pickles I n the case of pickles the fermentation is essentially the same as that involved in sauerkraut-i. e., the conversion of plant sugars into lactic acid and other products in salt solution in the absence of air. Certain physical factors, such as brine concentration, require close attention, since the sugars and juice must be extracted from the vegetable before the fermentation begins. Tanner (30),in a review of research in pickle fermentation, states : Despite the fact that this industry is an old one, much research may yet be done and must be done before it may be considered a controlled fermentation industry. There is great need for combined microbiological and chemical investigation. To date most of the work has been microbiological in nature with almost no attention to the chemical products which are formed by these microorganisms. Investigations must be instituted before the fundamental causes of softening, loss of color, hollow pickles, etc., will be clearly understood. Olives According to Cruess (7, 21), olives are picked when of full size and firm-that is, when they are light pink t o straw yellow in color. They are barreled for shipment to the factories and then handled similarly to cucumbers. The brine strength is increased to above 25 degrees salinometer, and the olives undergo a lactic fermentation. The texture becomes firmer, and the sugars are changed to lactic acid. During the curing process the oil content decreases slightly and most of the tannin and sugars disappear. During the lye treatment and subsequent leaching of green olives, there is danger of removing so much of the fermentable sugar and mannite that the olives will not ferment properly, To replace the fermentable material so lost it is advisable to add about 1 per cent refined corn sugar to the brine in the fermentation barrels. Vinegar The fermentation of plant sugars into vinegar (6,12, 13, 17, 18, 22, 28, 35) involves different types or organisms and different conditions of fermentation. Here sugar is first broken down into alcohol and carbon dioxide by yeasts. The alcohol is then attacked by certain types of bacteria, which convert it into acetic acid, probably through the acetaldehyde stage. Oxygen is necessary for this conversion and is ob-
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tained from the air by aerobic bacteria. This is accomplished commercially by trickling the alcohol solution down over wood shavings inoculated with the acetic bacteria. The production of vinegar must be well controlled, for if insufficient air is present the fermentation will stop a t the acetaldehyde stage. Further, if too little alcohol is present the acetic bacteria will attack the acetic acid already formed, convertingit into carbon dioxide and water. I n this fermentation the microorganisms which convert the alcohol into acetic acid must generally be added in order to obtain rapid and complete conversion of the alcohol and to prevent the development of objectionable types of bacteria. Nost commercial table vinegars are made from apple juice, but excellent products have been made from other raw materials, such as honey, peaches, pears, grapes, oranges, pineapples, and other fruits. Sorghum and corn sugar have also been fermented into good vinegars. It is of interest that hardly any of these materials yield vinegars which carry any flavor of the original fruit or plant material. Food Products from the Orient Staple food products prepared by molds constitute an important part of the food products of the Far East. Dyson (9) has given an interesting description of the method of manufacture of soya sauce, which is widely used in condiments of the Worcestershire type. Two organisms, an ilspergillus and a Zygosaccharomyces, are utilized. Soy beans and roasted wheat are the original raw materials. The meatlike flavor of this product is due to the presence of sodium glutamate. Church (6)in this country has made a critical study of soy and related fermentations. Cheeses
T ~ y otypes of cheese (8) are of particular interest. Camembert is a soft rennet cheese made from cow's milk. I n the curing of this cheese proper conditions of humidity and temperature must be maintained in order to develop the needful mold, Penicillium camernberti, the bacteria and yeasts. Following the growth of the mold other organisms develop, giving the cheese a reddish appearance instead of the white and blue, which is produced in the initial mold fermentation. Roquefort cheese, made either from sheep's or cow's milk, is also a soft rennet cheese, characterized by the marbled or mottled appearance of the interior due to the development of Penicillium roqueforti,which is the principal ripening agent. Fermented Milks Fermented milks (27) have long been used throughout the world, but only in recent years has increased attention been paid to their possible therapeutic value. Of these, acidophilus milk has attained a phenomenal popularity. The organism used in its preparation, Lactobacillus acidophilus, is a normal inhabitant of the intestinal tracts of infants. By ingestion of this milk implantation and proliferation of the organisms in the intestines are rapidly accomplished. Preservation of Fruit Juices The small amount of oxygen present in fruit juices, even after vacuum treatment, appears to be the factor limiting their successful preservation. To overcome this difficulty Ayers ( 1 ) has suggested an interesting method which consists in the inoculation of the juice with selected pure cultures, then sealing in a vacuum or reduced oxygen tension, and allowing it to stand for a predetermined period before pasteurization, during which there occurs a further reduction of the available oxygen.
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Conclusion Various food products of a n approximate annual value of one billion dollars utilize fermentation processes in their preparation. Many of these reactions are not clearly understood, and the field is a most promising one for the collaboration of the chemist and microbiologist in the solutions of problems of such scientific interest and high economic value. Literature Cited Ayers, Glass Container, 8, No. 11, 16 (1929). Bailey, “Sanitary a n d Applied Chemistry,” Macmillan, 1906. Bennion, “Bread Making,” Oxford University Press, London, 1929. Bitting, Fruil Products J . A m . I.i?tegar I n d . , 8 and 9, March t o S o vember (1929). Boutroux, “Le pain e t la panification,” Paris, 1897. Church, U. S. Dept. Agr., Bull. 1162 (1923). Cruess, Canner, 65, No. 6 , 17 (1927). Doane, Lawson (and revised by Matheson), U. S. Dept. Agr., Bull. 608 (revised 1928). Dyson, Pharm. J . , 121, 375 (1928). Evans, Tea Quart. (Ceylon), 2, Pt. 2, 44 (1929). Fabian, blich. Bgr. Expt. Sta., Circ. Bull. 85 (1926). Fisher, ‘‘Flour Quality,” Tech. ed., Sec. 3, National Joint Industrial Council, London, M a y , 1929. Hassack, Fruit Producls J . A m . Vinegar I n d . , 8, 19 (November, 1928); 24 (January, 1929); 30 (March, 1929); 18 (May, 1929); 19 (July, 1929).
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Joffe, “Breadmaking,” Colonial Salt Co., Akron, Ohio, 1927. Kent-Jones, “Modern Cereal Chemistry,” Northern Publishing Co., Liverpool, 1927. Knapp, J . Soc. Chem. I n d . , 43, 402, 430 (1924). Lawyer, Fruit Products J . A m . I*inegar I n d . , 8, 9 (October, 1928); 16 (Kovember, 1928); 20 (December, 1928). LeFevre, U. S. Dept. Agr., Farmers Bull. 1424 (1924). LeFevre, U. S. Dept. Agr., Circ. 35 (1928). Lehmann, Centr. Baht. Parasilenk., 16, 350 (1894). Lesley, Cruess, and Kaloyereas, Canner, 65, No. 13, 17; S o . 14, 21 (1927). Loesecke, v., IND. END.CHEJI., 21, 175 (1929). Marten, Peterson, Fred, and Vaughn, J . A g r . Research, 39, 285 (1929). Parmele, Fred, Peterson, IIcConkie, and Vaughn, I b i d . , 36, 1021 (1927). Pruess, Peterson, and Fred, IND.E N G . CHEM., 20, 1187 (1928). Robeson, U. S. Patent 1,313,209 (August 12, 1919); Tea C o f e e Trade J . , 39, 46 (1920); 41, 456 (1921). Rogers a n d Albus, U. S.Dept. Agr., Bull. 319 (revised 1928). Slyke, Van, N. Y . Agr. Expt. Sta., Bull. 268 (1904). Smith, “Fermentation of Cacao,” John Bale Sons and Danielsson, London, 1913. Tanner a n d Eagle, Canning Age, 1926, 651, 713, 783. Tibbles, “Foods, Their Origin and Manufacture,” Balliere, Tindall & Cox, London, 1912. Trigg, Tea Co-fee Trade J . , 39, 440 (1920). Whymper, Allen’s Commercial Organic Analysis, Vol. VII, p. 552 (1929). Wihlfahrt, “Treatise on Baking,” Fleischmann, 1927. W y a n t , Mich. Agr. Expt. S t a . , S p e c . Bull. 98 (1919).
Production of Fuel Gas by Anaerobic Fermentations’ A. M. Buswell ILLINOIS STATE WATERSURVEYDIVISION,URBANA,ILL.
This paper traces the early studies of production of S T I L recently anaeroused for heating and lightmethane by anaerobic fermentation, and summarizes bic f e r m e n t a t i o n s ing a t the disposal works. recent work in t h a t field. The chemical reactions have not been recogI n 1911 a c o m p a n y w a s involved in the decomposition of Iats, proteins, and nized as means for producing formed in Australia for the carbohydrates by anaerobic bacteria are discussed. valuable products, although purpose of producing and usA general formula is proposed for the reaction of t h e they h a r e been used for many ing fuel gases which resulted acids of t h e aliphatic series of acids, and data are f r o m the biological decomyears for the purpose of stapresented to show t h a t t h e fermentations described bilizing waste organic matter position of municipal wastes. result in a 90 per cent conversion of t h e material used and rendering it inoffensive. I n this country in 1915 into stoichiometric yields of carbon dioxide and methThe septic tank is the most Hommon e q u i p p e d s o m e ane. The commercial possibilities of the use of this waste-treatment tanks with commonly known example of fermentation process for the production of power gas gas collectors and used the this use. Unfortunately the from waste material are pointed out. gas. I n 1920 John Watson, earlv inrestiaators of waste of Birmingham, England, retreatment h a i their attention so firmly focused on the recovery of fertilizer in the form of ported a study of methane production from sludge digesthe solid sludge that the importance of the gaseous products tion and called attention to the fact that a considerable amount of methane can be produced in this way. Followof the process escaped their attention. It has long been known that one of the products of the ing his suggestion, the new disposal plant which has just decomposition of organic matter by bacteria is methane. been put into operation by his successor, Mr. Khitehead, The presence of methane in bubbles which rise from swamps is equipped with gas engines that are being operated on the or from the bottom of lakes or ponds where there is consider- gases produced from sludge digestion. This use of the gas able decomposing organic matter was early recognized, and cuts down Tery materially the operating cost of the disposal this accounts for the common name “marsh gas.” Some of works. I n the meantime (1926) Imhoff in Germany had the early Tvorkers in the field of bacteriology. studying the equipped the sludge-reduction tank in Essen (Figure 1) with decomposition of pure cellulose, obtained methane among their gas collectors and connected them to the city mains. The gas products, but the quantities obtained were not generally re- is found satisfactory for general municipal use and is sold corded, and the time required for the fermentation to take to the city. I n the same year Buswell and Strickhouser obplace TT-as so great that no practical importance was attached served that the sludge-reduction tanks a t Decatur, Ill., were producing about 200,000 cubic feet of gas a day. This large to the formation of this gas. It was not until 1897 that a waste-disposal tank serving yield is due to a considerable amount of wastes from a starch a leper colony in Matunga, Bombay, was equipped with gas works which are discharged into the city drainage system. collectors and the gas used to drive gas engines. At about The average yield a t Decatur is about 126,000 cubic feet of the same time the waste-disposal tanks a t Exeter, England, gas per day. The composition of the gases evolved by sludge-digestion were partially equipped with gas collectors and the gas was tanks varies somewhat. I n open tanks the methane is fre1 Received September 15, 1930.
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