MICROBIOLOGY OF ALCOHOL AND ALCOHOLIC PRODUCTS. 427 



CONTROL or THE MICROORGANISMS. 



Given grapes of suitable composition, the quality of the wine depends 

 on the work of microorganisms. The art of the wine maker consists 

 almost entirely in the control of these microorganisms. His success in 

 facilitating the work of the useful form (true wine yeast) and in preventing 

 or hindering the work of injurious forms determines the quality of his 

 product. 



BEFORE FERMENTATION. On the skins of sound ripe grapes as they 

 hang in the vineyard the microorganisms are comparatively few and in 

 an inactive condition. With the utilization of intelligent methods 

 they cannot injure the wine. On broken or injured grapes, the number 

 is greater and the forms more active. If many such grapes occur they 

 should not be mixed with the sound grapes if the best wine is to be made. 



Care should be taken to avoid unnecessary bruising of the fruit if it cannot be 

 worked immediately. Molds, wild yeasts and acetic bacteria multiply rapidly on 

 grapes wet with juice. 



The sooner the grapes can be crushed and placed in the fermenting vat or 

 pressed the easier it is to obtain a sound fermentation. 



Cleanliness is essential. Grapes, which are gathered in moldy, vinegar-soured 

 boxes, hauled in dirty wagons or cars, and passed through dirty crushers, conveyors and 

 presses, may be so completely infected with injurious germs that it is impossible to 

 obtain a good fermentation. The most injurious forms of dirt are must, grapes, or 

 wine, which have been allowed to become moldy or vinegar-soured. 



Dust or soil is less injurious and, if excessive, may often be removed by sprink- 

 ling, especially is this true if the grapes are too sweet and require dilution. Washing with 

 antiseptics is not permissible. A weak solution of potassium metabisulphite might be 

 used with benefit if it were not for the difficulty of regulating the amount of sulphurous 

 acid entering the fermenting vessel. 



If the grapes have to be kept for some time before crushing they should be kept 

 as cool as possible to delay the growth of molds. Gathering in the cool of the morning 

 is desirable and if grapes are gathered when warm they should be left in boxes to cool off 

 during the night whenever possible. If the grapes are cool when they reach the fer- 

 menting vat they will neutralize a certain proportion of the heat of fermentation, 

 accordingly the difficulty of avoiding injuriously high temperatures is diminished. 



However carefully the grapes are handled, a certain amount of dust containing 

 germs and other injurious matters will reach the vats and presses. In the manufacture 

 of white wines, especially, it is desirable to get rid of these matters before fermentation. 

 This is best accomplished by settling and decantation. 



As the juice runs from the press it is pumped into a settling tank or cask. If it is 

 cold, below 15, and of full normal acidity, the impurities may settle in twenty to forty- 

 eight hours. If the temperature is higher than 15 and the acidity low, molds and yeasts 

 will develop or fermentation will start and prevent settling. A slight sulphuring with 



