24 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



and the quality of his water, yeast, and 

 fermentable materials, his yields of alco- 

 hol may approximate those indicated or 

 may, on the other hand, fall far below it. 



Nature of Teast 



Yeast, the exciting agent of the alco- 

 holic fermentation, is familiar to the gen- 

 eral public chiefly in the form of the 

 small square cakes which are sold at 

 groceries, and to workers in breweries 

 and distilleries as a more or less frothy 

 paste. Whatever its outward form and 

 appearance may be, it always is made up 

 of innumerable microscopic plants which 

 are globular or ovoid in form, approxi- 

 mately 1 4000 inch in diameter, and fairly 

 colorless and transparent as seen under 

 the microscope. Yeast withstands pro- 

 longed exposure to cold without serious 

 injury, but is weakened rapidly when 

 kept at high temperatures, and is killed 

 quickly when heated to about 110 degrees 

 Fahrenheit. It ordinarily reproduces it- 

 self by a process of budding, and grows 

 at the expense of various nutrient ma- 

 terials, such as lime, potash, phosphoric 

 acid, and nitrogenous compounds, which 

 it absorbs from the solutions in which it 

 is placed. The vigor of a fermentation 

 seems to depend largely upon the phenom- 

 enon of yeast growth. Good fermentation 

 can not be established without abundant 

 and suitable nutrients for the yeast and 

 its vigorous development. 



The selection of a suitable yeast for 

 any purpose and its preparation and 

 maintenance in a pure and vigorous condi- 

 tion are arts which demand thorough 

 training and experience. They can not 

 be learned from books alone and call for 

 no small amount of manipulative skill. 



Preparation of Saccharine Solutions for 

 Fermentatiou 



Certain saccharine materials, such as 

 the juices of most fruits and of the sugar 

 cane, are in their natural condition so 

 susceptible to fermentation that they can 

 not be preserved unaltered unless they 

 are sterilized in sealed bottles or some 

 antiseptic or preservative material, such 

 as salicylic acid, is added. Other sugar- 

 containing materials, such as molasses, do 



not ferment readily until they have been 

 subjected to certain preliminary treat- 

 ments. Thus, both cane-molasses and beet- 

 molasses must be diluted with water be- 

 fore they can be fermented; and since 

 they often are deficient in the nitrogen 

 compounds which are essential to yeast 

 production it sometimes is found neces- 

 sary to add nitrogen to their solutions in 

 the form of ammonium sulphate or some 

 equivalent material. Furthermore, beet- 

 molasses is usually alkaline, and as yeast 

 will not work in alkaline solutions it is 

 necessary to acidify beet-molasses before 

 adding yeast to it. Diluted sulphuric acid 

 is commonly used for this purpose. The 

 amount of water or of chemicals which 

 must be added to a given quantity of mo- 

 lasses to fit it for fermentation will de- 

 pend upon the composition of the latter. 

 Experience has shown that with ordinary 

 cane-molasses it is desirable to use about 

 six volumes of water for one of molasses. 

 In this way a solution is obtained which 

 contains about 12 per cent of sugar and 

 is capable of producing approximately 6 

 per cent of alcohol. This proportion of 

 sugar has been found, in general, to give 

 the best results with regard to the rate, 

 completeness, and economy of fermenta- 

 tion. 



Preparation of Fermentaljle Solutions 

 from Starchy Raw Materials 



While the saccharine raw materials of 

 the fermentation industries can be pre- 

 pared lor use by the relatively simple 

 processes of solution or juice expression, 

 such materials as potatoes and grain, 

 which contain little sugar and much 

 starch, must be subjected to special treat- 

 ment in order to convert the insoluble and 

 unfermentable starch into sugar. The 

 series of operations by which this starch 

 conversion is accomplished is called 

 "mashing." and consists of a preliminary 

 scalding or cooking process, the purpose 

 of which is to liquify the starch, and of 

 the saccharification proper, in which the 

 soluble starch is converted into dextrin 

 and sugar. The agency by which the 

 latter conversion is accomplished is the 

 specific action (in the presence of mois- 

 ture, and at a suitable temperature) of 



