27 



tauj^ht the Chinese the art ot husbandry, and the method of making 

 bread from wheat, and wine from rice. 



In the process of wine makino^, the grapes, as soon as they are 

 picked, are carried to a suitable vessel and there pressed. The juice of 

 the grape, called "must," together with the skins, is then placed in a 

 large vat ; and the yeasts, which are always present on the surface of 

 ripe fruit, begin to grow, and in their growth produce alcohol and gas. 

 This production of alcohol is called the fir^t fermentation ; and when it is 

 nearly over, the wine passes through a strainer into a cask to undergo 

 the second fermentation. This cask fermentation lasts for several months, 

 and during this time flavouring substances are formed which give the 

 aroma, or bouquet, to the wine. The high price of certain wines is due 

 to the excellency of their aroma, which is largely a product of the yeast- 

 plant. 



Sometimes injurious forms of } east get into wine, and cause wine 

 diseases. One of the commonest is a yeast-like plant which changes the 

 alcohol into vinegar, and gives the wine a sour, or vinegar, taste. 



Cider and perry mav be regarded as the wines of those districts in 

 which the grape does not flourish. Cider is the juice of the apple fer- 

 mented with yeasts that are naturally present on the surface of the fruit, 

 and perry is the fermented juice of the pear. 



Barley, yeast, and hops are used in the making of beer. The 



barley is allowed to germinate, or 

 sprout, in order to change the starch 

 of the kernel of the barley into sugar. 

 This material, extracted by means of 

 hot water, is the food in which the 

 yeast plant grows and produces alcohol 

 and carbonic acid gas. 



Other substances are used to give 

 flavor to the beer ; but the essential 

 part of the making is the changing of 

 the sugar solution into alcohol by 

 means of the }east plant. 



Special varieties of yeasts are used 



to make diff'erent kinds of beer, as ale, 



lager beer, etc. ; and, as in the case of 



wine, disease-producing yeasts very 



.often appear and produce a cloudy, or 



fied, the natural' size "i.eiii- only one-thou- turbid, Hquor, which is disliked by those 



II in the fijfure. , i • i 



who use such dnnks. 

 From a study ot the changes in bread, wine, etc., we see that 

 the yeast plant, in order to grow, requires a proper supply of food, 

 which should consist of a mixture of nitrogenous substances, a certain 

 amount of carbon (usualh' supplied in the form of sugar), and also 

 mineral matter. About 20 per cent, of water is also necessary, and a 

 suitable temperature, between 60 and 90 degrees Fahrenheit. If these 

 conditions are present, the yeast-plant is able to live, grow, and pro- 

 duce other yeast-plaiits. 



'. ^ 



\ 

 V 



Fig- 31. Full <;-ro\vn yeast plants greatl.v magiii 

 fied, the natural size liein 

 sandth-part of the size show 



