Page:The American Cyclopædia (1879) Volume VII.djvu/150

FERMENTATION the conversion of the sugar into lactic acid, which is evolved in considerahle quantity if the malt is allowed to cool in a moist state. The action of dilute acids, assisted by heat, also has the power of converting starch into dextrine and grape sugar. (See DEXTRINE.) 2. Alcoholic or Vinous Fermentation. If a decoction of malt is allowed to stand for a time in the open air at a temperature varying from 40 to 85 F., a change takes place, in which bubbles of carbonic acid gas may be seen to rise from the mass ; and upon exami- nation it will be found that portions of the sugar and gluten have disappeared, and in their place will be found alcohol, lactic, acetic, and succinic acids, and some glycerine, in varying proportions, depending upon the temperature and the amount of saccharification that had taken place in the malt. There will also be found more or less of a viscous substance con- taining yeast cells and germs and other micro- scopic organisms, and some mannite. If, how- ever, instead of allowing the decoction of malt to ferment spontaneously, it be kept at a tem- perature of 158 to 167 F. until most of the dextrine has been converted into glucose, and then filtered and cooled to 70 or 85 with suffi- cient rapidity to prevent the commencement of premature fermentation, and then a quantity of brewer's yeast which has been kept in a warm place until it begins to 'decay be stirred in the mass, brisk fermentation will soon be induced, by which nearly all the glucose will be transformed into alcohol and carbonic acid, as represented in the following equation : C C II ]Q 0, Glucose. 2C 2 H 6 + 2C0 2 Alcohol. Carbonic acid. Under the most favorable circumstances not more than 95 per cent, of the sugar passes into alcohol and carbonic acid, the remainder being converted into succinic acid and glycerine. Both these bodies are formed, according to Pasteur, as follows : 49C 6 H 12 6 + 30H 2 = 12C 4 H 6 4 + 72C 3 H 8 O 3 + 80C0 2 Glucose. Water. Succinic acid. Glycerine. Carb.acid. The production* of succinic acid in alcoholic fermentation was discovered by C. Schmidt in 1847. Pasteur discovered a few years ago that glycerine was also one of the products. Amylic alcohol or fusel oil is also frequently produced in alcoholic fermentation. Cane sugar, Ci 2 H 2 2 On, does not pass into alcohol and carbonic acid directly, but is first converted into glucose by assimilating one equivalent of water, thus : C 12 H 22 O 22n H 2 r. Water. 2C fl H 12 6 Glucose. It then passes into alcohol and carbonic acid as before represented. Milk sugar, Ci 2 H 24 Oi 2 , which has the same proportion of elements as grape sugar, but with a different molecular ar- rangement, is also transformed into alcohol and carbonic acid under the influence of cheese or other proteine bodies in a state of decay ; first passing, according to some observers, into glu- cose. Must of grape or juice of fruit, if boiled and suspended in a bladder in the midst of fermenting must or wort, will not ferment; and it has been stated that if yeast cells be prevented from coming in contact with the fermentable liquid, fermentation will not take place, although the soluble contents of the cells may pass through the membrane. Should this statement be substantiated by further ob- servation, it would go to show that the exceed- ingly minute germs of yeast cannot penetrate through the coats of animal membranes, al- though so small as to be scarcely visible under a magnifying power of 2,800 diameters, and would also show that fermentation, whatever may be the question as to its being itself a vital process or a chemical one, cannot take place without the influence of these vitalized germs. ' Yeast, torula cerevisice or mycoderma vini, is a fungoid vegetable organism, composed of mi- croscopic globules which attain a maximum diameter of about ^-^ of an inch. Each globule is composed of a thin membranous cell wall having the composition of cellulose, C 6 Hio0 6 , and is filled with a gelatinous proteine compound, principally consisting of exceeding- ly minute germinal granules. There are two varieties of yeast, depending upon the mode of propagation. When fermentation is con- ducted below 45 F., the propagation is carried on by an increase of the germinal granules within the cells by assimilation of nutriment from the fermenting liquid, until the cell wall bursts and the partially organized granules which are liberated proceed in their develop- ment, forming in turn parent cells. Yeast formed in this manner is called by the German brewers bottom yeast (Unterhefe), and is the kind used in the fermentation of Bavarian beer. It is deposited during the process at the bot- tom of the fermenting tun in the form of a grayish viscid or gelatinous mass, the yeast being more or less mixed with other sedimen- tary matter. TVhen, however, the temperature at which the fermentation is conducted is much above 45, say from 70 to 85, the develop- ment of germinal matter becomes much more rapid, and it passes, according to Dr. Lionel Beale, through pores of the parent cell wall, per- haps carrying a thin pellicle with it, and makes its appearance upon the outside in the form of what have been called buds, first discovered by Cagniard de la Tour. (See fig. 1.) These buds, which for a time remain attached by pedicles to the parent cells, then go on developing, and in time become detached and assume the functions of parent cells ; or buds may spring from them before their separation, and thus branches ex- tending to some distance may be formed, as in fig. 2. Fig. 3 exhibits an appearance often noticed : several buds growing from one parent cell, each filled with granular matter, and presenting an irregular outline. On account of its branching structure, yeast which grows in this way becomes buoyant from the collec-