INDUSTRIAL AND ENGINEERING CHEMISTRY
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narily supplied in the forms of gluten from grains or ammonia and phosphates. The lactic bacteria are susceptible to an excess of acid; hence the acid must be neutralized as it is formed in order for the culture to thrive. This is usually accomplished by the addition, a t the beginning of a fermentation, of sufficient calcium carbonate to neutralize the acid as produced. However, a very slight acidity is sometimes maintained during the fermentation to prevent the growth of contaminating organisms. This is done by the gradual addition of lime as required, but very close control is necessary in order to maintain a uniform acidity. A fermentation usually requires 5 to 6 days for complete conversion of the sugar to lactic acid, although the time may vary widely with conditions. When it is completed, sulfuric acid is added and the calcium lactate converted to lactic acid and calcium sulfate. The latter is filtered off and washed. The resulting weak lactic acid (about 8 per cent) is concentrated in vacuum pans to the desired strength. Grades
The lactic acids of commerce may be classified as “technical” and “U. S. P.’J The technical class may be further subdivided into “dark,” “light,” and “edible,” according to the color and to the degree of purification during processing. The dark grade is generally produced from molasses and the light and edible grades from starch or sugar. The preparation of the edible grade is similar t o that of the light grade except that more extensive purification treatments are required to remove heavy metals, etc., which would be objectionable in foods and beverages. The technical grades of acid are usually marketed a t strengths of 22 and 44 per cent, although other strengths may be supplied if desired. The U. S. P. grade of acid is not produced in this country, but is imported from Germany. It is a water-white or very slightly yellow product produced by purification of the technical grade and contains 85 per cent of lactic acid. The containers in which lactic acid is shipped are wood tank cars, hardwood barrels, glass carboys, and smaller bottles. Uses
The leather industry is the principal consumer of lactic acid, utilizing probably 80 to 90 per cent of the entire con-
Vol. 22, No. 11
sumption of the country. Its most important function in leather processing is the removal of lime from dehaired hides. The solubility of calcium lactate, together with the mild effect of the lactic acid upon the hide substance, make it an ideal acid for this purpose. The technical lactic acid has t o a large extent displaced the old-time bran drench which was formerly used for deliming. The active constituent of the “soured” bran drench was lactic acid produced by natural fermentation; hence the technical lactic acid produces the same effects upon the leather. However, the technical acid has the great advantage of producing a drench of definitely controlled composition which tends to insure uniform and consistent results in this important step of leather production. Lactic acid is also used for plumping leather, but its advantages over other acids, such as sulfuric, hydrochloric, and oxalic, are not so pronounced as in the deliming operation. The dyeing and finishing of textiles constitutes an important field for the use of lactic acid, particularly in chrome mordanting and in acid dyeing of wools. I n recent years a large amount of lactic acid has been used in the production of ethyl lactate, a high-boiling solvent for the nitrocellulose used in the production of pyroxylin lacquers. The edible and U. S. P. grades of lactic acid are gradually finding increased uses in widely diversified lines of food and beverage products, some of which are infant foods, low-alcohol beers, soft drinks, candies, poultry, and stock foods. I n infant foods lactic acid appears to have a corrective effect upon the digestive tract; in near-beers its purpose is improvement of flavor and odor; in soft drinks and certain candies it acts as an acidulent replacing citric and tartaric acids. Its advantage over acetic in this respect is that the acidity of the product can be increased by the use of lactic acid without making the taste objectionable. I n poultry and stock foods certain advantages are claimed for lactic acid either as the commercial acid or its salts or in the form of buttermilk products. The wide natural occurrence of lactic acid in food products has accustomed the digestive tract to it. This, together with a mild pleasing taste and marked preservative qualities leads to the belief that the most important development of new uses for lactic acid in the future will be along the lines of food and beverage products.
History and Development of the Modern Yeast Industry’ Charles N. Frey FLEISCHMANN LARORATORIES, 1 5 8 ~ HST. A I D MOTTAVE.,
HE fermentation in-
NEW YORK,
N. Y.
The history of the yeast industry from the earliest spontaneous generation, The times down to the manufacture of the modern comfourth or modern period, foldustry has had severa1 distinct periods pressed yeast is outlined. The various theories of lowing thetime of Pasteur and fermentation which have arisen during the course of extending to approximately of development. One may the development of the industry are described. A 1914, also covered a further be called the period comprising the art of the ancients, inbrief survey of the uses and biological properties of development, the ammoniacluding the period antidating Yeast is given. molasses phase. It would be extremely inthe compressed-yeast industry; the second, the compressed-yeast industry before Pasteur; teresting if we could call forth representative men from the third, the period of scientific study of yeast which includes every one of the great nations which have existed since the the period of Pasteur and the period immediately afterward. dawn of civilization. We would ply them with questions This period is chiefly represented by two groups, one group regarding their system of philosophy and their interpretarepresenting the vitalistic and the other the chemical point tion of the laws of nature. What forces in nature did they of view. I n addition there was a group who believed in recognize and how did they succeed in controlling or combating them? It is impossible for us to conceive, even were di1 Received October ll, 1930.
T
November, 1930
INDUSTRIAL AND ENGINEERING CHEMISTRY
rections given us, all the methods used by the ancients in their arts and sciences. This is especially true of the fermentation industry. The origin of many of the processes which have come down to us is buried in the distant past and me cannot trace their source. Fermentation in Ancient Times
Recent discoveries have shown that the lake da-ellers of Switzerland had cultivated grains and were familiar with the making of bread. Possibly the bread they made was not a fermented bread. It is well known to us that the Egyptians mere familiar with the manufacture of flour, the making of bread, and the fermentation of beer. The beer mentioned in Egyptian times was probably connected with sacrificial rites. The Babylonians also had considerable information regarding the manufacture of beer, the fermentation of bread, and the milling and manufacturing of flour. We are told that two kinds of beer existed in Egypt-one made for the poor class of people which was dark and not properly clarified, whereas that made for the wealthier class was brilliant and well prepared. The Egyptians clarified their beers by means of fine clay. There also existed two kinds of bread-a refined white bread for the wealthy class and a coarse brown bread for the poor class. This condition also prevailed in Babylon. The Babylonians sprouted and dried the grains, ground them, and then mixed them with water and baked. The roasted malt loaves were then crushed and mixed with water, and crushed raw grains were added which probably carried the organism of fermentation. After fermentation the mash was filtered through straw mats and the spent grains were even washed or sparged. I n Egypt, Osiris was regarded as the god whose wisdom gave man the art of fermentation. The Egyptians had probably perfected baking and brewing a thousand or more years before the Christian Era. They ground the wheat, in either the wet or dry form, and subsequently the dough was fermented. This fermented dough was baked on slabs of stone or brick and possibly iron plates, in a well-constructed baking oven. Figures found in the tombs indicate that the Egyptians molded brick by hand but they worked the dough by treading it with the feet. The Egyptians also knew the advantage of adding salt. Their bread was undoubtedly made from wheat and barley. Most of the bread making was performed by the women of the household. The Jews distinguished between leavened and unleavened bread. They were probably familiar with the knowledge of both the Egyptian and Babylonian people. The Jews were familiar with brewing and in 257 A. D., Rabbi Huna, a brewer, was Rector Magnificus of the Jewish University in Tura. Probably the first statement of yeast action was made by St. Paul, when he said, “Know ye not that a little leaven leaveneth the whole lump?” The Greeks were in immediate contact with the Egyptians and the people of Asia Rlinor. They were familiar with the methods of bread making and they imported large quantities of wheat for food purposes. The Greeks did not adopt beer as a national drink. The fermentation of wine was probably a spontaneous process and its preparation seems to have been well understood by them. The Greeks are said to have sterilized their wines by heating. Belm of Crete states that wines were boiled before exportation. The significance of this statement was not appreciated until the work of Scheele and Appert appeared in the nineteenth century. The Romans produced a vesiculated type of bread similar to that made a t the present time. At least this is indicated by the researches a t Pompeii. Illustrations of women kneading dough on a board placed in a circular trough have been
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found. Professional bakers began to appear in Italy after the war with Perseus, according to Pliny. Previous to that time most of the work had been done by the women or by slaves. When baking became an industry, slaves were imported to do the work. Later criminals were selected to grind the grain and still later on power was applied, horses or oxen supplying the power. According to Pliny, the Romans were also familiar with mine making and seemed t o be aware of the fact that if the wine jars were stored too closely contagion would spread from one jar to another. Instructions indicate that they knew how much space was necessary t o insure the keeping of wine. Pliny states that new mine often turned to vinegar. The Slavic races of Russia prepared their own beer, called ‘lkwass,” by sour and alcoholic fermentation of wheat, barley, or rye, using sprouted grains and the flour of raw grains. A process of distillation was also known to them. We may conclude that the ancients possessed considerable knowledge regarding the art of fermentation. The Middle Ages
There is evidence that the bakers were well advanced in their technic in the Middle Ages. There existed regulations in regard to bakers and the weight of bread. I n France public baking ovens were in use. An entire village might operate one oven. Beer was brewed chiefly in the monasteries and by brewers after the twelfth century. The wealthy are said to have made their own beer. After the Reformation many of the monks who had been driven from the monasteries developed the commercial production of beer. Lager beers were made in 1300. Possibly the chief skill involved was in cultivating the stock yeast and in mashing the grains. Hops were introduced about 900 A. D. Albertus Magnus (1193-1280) and Roger Bacon (12141284) considered fermentation and digestion as analogous. No distinction between organic and inorganic material was made. T. B. Paracelsus (1493-1541) discussed putrefaction and fermentation, but no experimental work is cited to substantiate his theories. I shall not attempt to review the period of the Middle Ages but shall pass directly to the period covered by more recent historical documents, especially the work following the discovery of bacteria by Leuwenhoek in 1685. The Period before Pasteur
I n 1775 Krunitz wrote an encyclopedia on yeast, in which he stated that the yeasts are those bodies existing in the liquid during fermentation and which are driven to the surface and later settle to the bottom-that is, when the fermentation is completed. This is believed to be the first definite statement in the literature regarding the nature of the substance causing fermentation. Kriinitz also said that good results were obtained if one took the yeast which had been obtained in the course of fermentation and added wheat flour, a small amount of sugar, and some wort, and placed it in a warm place. He recognized the importance of culturing the yeast. The follon-ing are some of the important figures who contributed to the development of the art of yeast making. Ton Justi (1720-1771) described methods for preparing “Kunsthefe.” Westrumb (1751-1819) advanced the art of making stock yeast by improving the methods of preparing the “sauerteig.” He showed how to prepare the wort by proper malting, addition of hops, and temperature control. He also advised the use of the thermometer. Hermstadt (1760-1833) advocated the use of lorn temperatures for the mash. He did not understand the true nature of the substance initiating fermentation, but he developed
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good technical methods. I n 1819 he stated that the top yeast was purer and better than the bottom yeast. It had a tendency to gather at the top and run from the bunghole of the fermenting tuns. He also described a method for determining the good yeast by dropping a spoonful into boiling water. If the yeast floated on the surface similar to lard it was a good yeast, but if it sank to the bottom it was a poor yeast. He tested his yeast by mixing a quart of yeast with a teaspoonful of brandy, some sugar, and a spoonful of wheat flour and allowing the mixture to stand. If the yeast was good it promptly started to ferment. He also introduced a saccharometer. Benno Scharl, Riem, l’istorious, and Dorn made improvements in the preparation of “Kunsthefe.” Pistorious introduced an improved distillation apparatus for the separation of alcohol from the mash. Fremg and Boutron about 1839 studied the souring of the wort. Scheele had observed that an acid was produced in the souring of milk and in the production of sauerkraut. The sour produced in the mash was regarded by many as acetic acid in spite of the work on the structure of lactic acid published by Gay-Lussac and Palouse in 1833. Fremy and Boutron added enzymes from the stomachs of dogs, and later from calves’ stomachs, to worts, and observed the formation of lactic acid. Liebig was interested in these experiments because he thought it proved that his ideas of the nature of fermentation were correct. They also noted that the lactic ferment would produce acid and that when the production of lactic acid reached a certain point it was stopped on account of the high degree of acidity. By neutralizing the solution the production of acid was resumed. About 1800 compressed yeast began to be known in England, Holland, and Germany. The first compressed yeast was prepared by an Englishman named Nason about 1792. This yeast was prepared without hops. About 1800 the Dutch process a t Schiedam became known, but it is reported that the yield was only from 4 to 6 per cent. It is believed that the mash was made from rye and malt, diluted to 10” Balling, and seeded with yeast a t a temperature of 18-19’. Ton Dunndorf in 1817 stated that a compressed-yeast process had been operated in Holland since 1781 and consequently it was often difficult to dispose of the beer yeast. The bakers and housewives were in the habit of obtaining their yeast from distillers and brewers and possibly when the compressed yeast was developed it proved to be a better fermenting material than beer yeast. Formulas are also given in the literature in regard to the preparation of starting yeast. These preparations were used by housewives and bakers and possibly also by the brewers and distillers. I n 1822 a chemist by the name of Tiele pointed out the value of malt, which he stated mas due to its sugar. He did not recognize the presence of diastase in the malt. He regarded yeast as a sort of gluten which changed starch into sugar and sugar into alcohol and carbon dioxide. This idea of the nature of yeast was expressed by Fabroni in 1799. I n 1833 Tebenhoff showed that distillers’ yeast or top yeast was better than beer yeast for bakers. Gutsmuth described a process for growing yeast which he obtained from Holland. This process was so well conducted that he was able to carry on his operations during both the summer and winter. Temperature control was becoming an important factor. Yon Plonitz and Xubry froze yeast and stored it in a frozen state. One of the most prominent men in the fermentation industry in the early part of the nineteenth century was Ludersdorff. He developed methods for souring the wort, improved methods of selecting the stock yeast, and introduced
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methods of control, such as the use of an improved saccharometer, the thermometer, and a process for the preparation of stock yeast. Ludersdorff also investigated the nature of the malt used in the preparation of the yeast. He developed a method for determining acidity in the sour wort as well as in the yeast mash. He knew the advantage of using acid to prevent contamination and to stimulate growth. He also introduced the microscope into the fermentation industry. Ludersdorff pointed out that the addition of hops mould prevent contamination in the fermenting mash. As a scientist he contributed information which greatly influenced the work of Liebig, Pasteur, and Mitscherlich. The results of Quevenne in 1838 on the toxic action of acids and alkalies were verified and applied to the industry by Ludersdorff. Otto in 1840 began mashing at approximately 40-50°C. and used steam in his manufacturing process. He soured with sulfuric acid using 0.5 to 1000 liters of wort. He obtained 6 to 8 per cent yield of yeast when he prepared his own stock yeast and obtained practically three-fourths of the theoretical yield of alcohol. Balling in 1845 published an important work on fermentation. His development of the saccharometer was a great achievement and enabled the operator to control the mashing of his grains and the fermentation of the wort. Stammer introduced improvements in the determination of acidity in worts and fermenting solutions. Mautner in 1846 used corn to replace part of the rye in the mash. He used malt for the conversion of starch. He also refrigerated by putting ice in the cellar and was the first to obtain uniformly good temperature control. Later he built a factory in which he stored ice on the second floor and carried on his fermentations on the lower floor. Paupie in 1 i 7 1 was familiar with a method of preparing dry yeast by means of ashes; the yeast and ash were wrapped in cloth and dried in the sun. The first dried yeast was sold in Vienna in 1822 by Burka. Previous to that time other methods of preserving yeast had been described. One method, described before 1800, was to place the yeast in a bottle and add oil t o cover it and then bury it several feet in the ground where it would remain cool. Other methods consisted in wrapping the yeast in cotton or cloth, removing as much moisture as possible by the addition of wood ashes, drying this material in the sun. and then storing it until further use. Hops were also frequently added. Recognition of Various Types of Fermentation At the time of Ludersdorff and in the early period of Pasteur several types of fermentation began to be clearly distinguished-(1) acetic, (2) lactic, (3) alcoholic, and (4) putrefactive. In order to follon- the growth of these conceptions, we shall return for a moment to the scientific development of the ideas on fermentation. The yeast industry was awaiting the application of the new ideas in science, and fortunately those who so eagerly approached the problems Tvere able to make great contributions. The following summarizes briefly the so-called scientific period comprising the vitalistic and chemical theories which arose prior to Pasteur. Scientific Period CREhfICAL THEORIES O F FERMENTATIOS-In 1659 SylViUS deBoe distinguished between fermentation and other reactions in which gas is given off. In 1669 Becher stated that only sweet solutions underwent fermentation. Somewhat before this time Van Helmont (1577--1644) observed that fermentation was produced by a specific agent, but did not ascertain what this substance was. He found that gas is present in the fermentation of wine.2 However, in 1659 2
Van Helmont named this “gas syl! estre.”
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IL1'DUSTRIdL AiYD ELVGINEEIZIAVG CHEMISTRY
Willis stated that fermentation was caused by a substance which, owing to its molecular instability, communicated its vibration to other substances present in solution. Sta!il (1660-1734) elaborated this theory and gave an explanation of fermentation which was accepted up to the time of Liebig, who became the most eminent protagonist of this view. 131a(.k (1728-99) showed how to distinguish gases from each other, and stated that, carbon dioxide is tlie only product formed, aside froiri alcohol, in the transforination of sugar. McBride found that approximately all fermentation gases contained carlion dioxide. He established the identity of carbon dioxide as one of the gases given off duriiig fermentation, and Caveiidish found that approximately 57 per cent of the gase. given off during fermentation of sugar consisted of carlmi d:oxide (fixed air). -1further derelopnient in the cliernical idess of feriiientatioii occurred ~vlienLavoisier (1743-94) applied himself to the solution of this prohleni. I n 1789 he stated that during t'ermr,ntation alcohol and carbon dioxide are forined. ier undertook tlie fir3t quantitative d u d y of tlie products of alcoliolic fermentation of sugar. His analytical results n-ere inaccurate, hut lie correctly pointed out the iriiportant fact that the sugar lireaks u p into akoliol. cariioiiic acid. and n-hat lie regarded as acetic acid, n-itliout any addition of matter from extranmis sources. Tlierefore. the agent causing the fernientation doe? not coiitriblite any material. According to Lai-oisier. 95.9 parts of sugar yield 57.7 per cent aIc:ohol, 33.3 per cent carbonic acid. aiid 2.5 per cent acetic acid. ~vliicligives a total of 95.5 parts. The conclusions of' Lavoisier were later inT-estigated by Gay-Lussac and much later by Pasteur. Gay-Lussac foririulat ed t lie fo!l ou-ing equation :
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presence of albuniins it de2oniposes into alcohol and carbon dioxide. Liebig did not deny the presence of the yeast globules, but he did not accept the view of Pasteur that fermentation was a vital act of the yeast cell. The French chemist, Berthelot. also favored the chemical theory of fermentation. He believed that nitrogenous compouiitls, such as casein, are able to decompose sugar. Teast acts on sugar by virtue of its prot,ein. His studies on invertase led him to express the view that fermentation is due to enzynies. It is not yery clifficult to understand why Liebig came to the conclusion that fermentation is not a vital a:t. It1 1828 Kohler had synthesized u r w . I n 1811 Kirchhoff foulid that starch was transferred by mineral acids into glucose, and he shot!-ed that no acid was consumed in the process. I'ayen and Persoz in 1830 made the discovery that gcrrminsting seeds contain a suhstance which transforms starch into sugar. Liebig was also familiar with the enzyme einu!sin wliicli acts on aniygda!in. Davy in 1820 observed that finely divide1 platinum conr-erted alcohol t o acetic acid. I t is unfortunate that the views of Pasteur and Liebig were not adjusted. for Pasteur c!early perceired the posFibil~ty of t,lie living cell producing a suhstance which coni-erts sugar to alcohol and carlmn dioxide hy a p r o m s anslogous to that liy which emulsin decomposes amygdalin. To the statrnient c ~ fPasteur that, ferinentat,ion i p associated .ivit'!i the life of tlie cell, Liebig finally replied; "From the chemical standpoint a-!iich I loathe to give up, the act of a living orgsnisni is a species of niolecular \-illration aiid in tllis sense the \vorl
