230 MASSACHUSETTS AGRICULTURE. 



As an agent to excite fermentation, yeast in some one of its 

 many forms, is in this country more generally used than any 

 other. The active principle of yeast, and how it acts to chemi- 

 cally decompose the sugar of the flour so as to liberate the gas, 

 has ever been a mystery. The microscope has yet been able to 

 show little beyond the fact that it belongs to the vegetable 

 kingdom — that it is a plant of the fungus tribe. Under a 

 powerful magnifier, it is seen to consist of innumerable rounded 

 or oval bodies, which are the true vegetable cells. Each little 

 globule consists of an enveloping skin or membrane, containing 

 a liquid within. When placed in favorable circumstances, 

 these globules, each containing within itself the seminal princi- 

 ple, are rapidly multiplied by budding off from each other, and 

 so the plant is built up, and somehow its growth disturbs the 

 combination of elements that make up the sugar, and the 

 carbonic acid gas is set free. 



The most common form in which yeast has been made and 

 kept, is that of a liquid. In making yeast, the brewer is accus- 

 tomed to use malted grain, barley being preferred. The grain 

 is moistened and kept warm till it begins to sprout. In this 

 operation a chemical change takes place by which a portion of 

 the starch is changed to sugar. It is then dried, and the 

 process is stopped. In this state the grain is called malt. It 

 is next crushed and soaked in warm water, at a temperature of 

 about 160 degrees, to extract the soluble matter it contains. 

 Hops arc then added, and the liquid is boiled to coagulate the 

 excess of gluten ; and when again cooled yeast is added, and 

 the mixture is left to ferment. The malt gives strength and 

 activity to the yeast ; the hops serve to check the fermentation 

 before all the sugar is changed to alcohol, and to delay the 

 production of acid. 



But it has been found that yeast may be more conveniently 

 preserved by drying ; and manufactories of dry yeast are now 

 established in various places, and it is thus easy to procure a 

 good article with but little trouble. But many persons prefer 

 to make it for themselves, and it is easily prepared in tliis way : 

 boil three ounces of dry hops half an hour in a gallon of water, 

 and strain the liquid through a fine sieve into an earthen 

 vessel. While hot, stir in two quarts of wheaten or rye meal. 

 When lukewarm, add a half-pint of good yeast and let it stand 



