THE ferment used for raising the dough in making bread is a microscopic fungus, so-called yeast, or, as it is called by the biologist, saccharomyces cerevisise. This organism grows in saccharine liquids, reproducing by budding. Its cultivation constitutes quite an important industry, some of the essential steps of which, as carried out in Prance, are illustrated in the accompanying views. The raw materials in this industry are barley, rye, and Indian corn. The first operation consists in cleaning this material in special engines provided with metal brushes, sorters, and separators. After the dust and other adventitious material has been thus eliminated, a certain portion of the grain is passed through a mill and is. ground to flour. The remainder of the barley is taken to another part of the plant, located in the basement, where the operation of malting and germinating is carried on. In the course of this process a certain ferment, known as diastase, is developed in the grain, which has the property of transforming starch into fermentable sugars. Throughout the malting operation it is necessary to observe careful precautions in regulating the temperature and humidity, as these factors exercise an important influence upon the proper course of the process. The temperature commonly employed is from 12 to 14 deg. Cent. The ordinary method of germinating the grain requires an extensive floor area and great attention on the part of the workmen, and is more- The fermentation vats. over applicable only at certain times of the year, for if the malting is carried on during the hot weather, there is apt to be a very serious development of mold. This last inconvenience has been very successfully overcome by the so-called pneumatic malting process introduced by Galland and others. This consists simply in circulating through the grain a current of air whose moisture and temperature i s regulated accord-ing to atmospheric conditions and to the. particular phase in the process. The wet barley is placed in double-walled sheet-iron drums or cyl- inders, through which the regulated air current is passed, while the grain is slowly turned over by rotating the drum about its geometric axis, for which purpose the cylinder is mounted upon four rollers, and is provided at one extremity with a toothed wheel engaging a worm gear. The cylinder rotates once in about forty minutes. The charging and discharging is effected through a man-hole closed with a door, while a platform gives the foreman access to the drum and enables him to observe the progress of the operation. After some eight or nine days the germination is sufficiently advanced, and the diastase is fully developed. It is then necessary to stop the operation, for otherwise the young plant would continue to grow, giving rise to other changes than those which are the manufacturer's object. It is time to take the barley out of the malting drum and to proceed to the next opera-. tion, which consists in drying the grain at an elevated temperature. This is carried out in long rectangular rooms built of brickwork, and measuring about twenty-three by thirty-three feet in length and breadth, and about forty to fifty feet in height. In these hot rooms the barley is spread out upon sheets'. of metal gauze, in layers about four inches deep, and is allowed to dry gradually. A short chimney at the end of the building allows the escape of the water vapor liberated in the process of drying. After the trying operation is completed the grain is lext passed on to a riddle, whereby the root-ets formed during the germination are sroken and separated. The grain is next passed between cylindrical rollers which bruise it without grinding it to powder. The product is now mixed with water, whereby the so-called must or saccharine liquid for fermentation is obtained. The preparation of. this liquor is carried out in double-bottomed macerating tubs, heated by steam and provided with mechanical agitators. The materials fed into these tubs consist of a mixture in about equal parts of flour and barley, ttte diastase in the malted barley being sufficient to turn into sugar not only the starch contained in the grain itself, but a further quantity, furnished in the form of untreated starch. It is, of course, an economy to malt only a portion of the grain and make it do duty for saccharifying both its own starch and a further quantity upon which no malting operation has been performed. As soon as the saccharification is complete, the product, in form of a doughy slush, is introduced into double-bottomed capper coolers, in which it is cooled down to 20 deg. Cent. From the refrigerator the must is distributed to a number of tubs of 220,000 gallons each, arranged in a special room, whose temperature is maintained constant through summer and winter, as this is an indispensable factor for the successful operation of the process. The tabs are then inoculated with a quantity <of yeast carefully prepared. The temperature of the must reaches 25 deg. Cent, at the start, and must not be allowied to exceed 30 degrees. It is important to rigorously observe these limits of temperature and to be scrupulously careful in the preparation of the grain, in maintaining the right proportions for the mixture, and in insuring absolute cleanliness of every part of the plant. From time to time, until the fermentation is completed, the yeast is gathered from the surface of the liquid in the tub. The yeast is then sifted in order to separate it from the malt and the mucilaginous material admixed with it, whereupon it is passed through a filter press which delivers it in the shape of slabs or cakes. Finally, the yeast is stamped in a briquetting press and made up in parcels of one pound, two pounds, and one-half pound, which are carefully packed in double wrappers for delivery to bakers and pastry cooks. The must, on the other hand, after the fermentation is completed, is carried off to reservoirs in the cellar, whence it is pumped to the stills. By a series of suc- Cf AD” Foot and Power OlrllV Screw Culling Automatic I ATUIC Cross Feed LAHlEd For Fine, Accurate Work Send (or Catalogue B SENECA FALLS MFG. CO. 695 Water Street Seneca Falls, N. Y, U. S. A. 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CONN. cessive distillations, the alcohol is driven off, and collected for marketing in the form of “rectified spirits.” The residue from the distillation is drawn off to a large tank provided with a stirrer, and is then distributed, while still warm, to be used for cattle food, or it may be collected in large wooden reservoirs and shipped in bulk or in casks. This malt residue contains most of the original nitrogen of the grain and a certain quantity of dextrine and unconverted starch, and forms one of the most nourishing fodders for cattle. Another by-product of the industry is the carbon dioxide which is formed in the fermentation process. This may be liquefied and placed on the market in steel cylinders.
This article was originally published with the title "The Manufacture of Yeast" in Scientific American 105, 23, 494 (December 1911)