Sl6 MICROBIOLOGY OF SPECIAL INDUSTRIES 



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 pres^d 

 the easier itis to obtain a sound fermentation. 



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

 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-sour. 



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 diluti6n.* 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 kepi 

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

 ing 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 fermenting vat, they will neutralize a certain proportion of the heat 

 of fermentation, and 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 manu- 

 facture 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 the fumes of burning sulphur or with a solution of potassium 

 metabisulphite is therefore usually necessary. The sulphuring should be as light 

 as possible with acid musts as it tends to preserve the fixed acids. For the same 

 reason it benefits musts of low acidity. In from twelve to twenty-four hours, the 

 must is purged of all its gross impurities including dust, and solid particles de- 

 rived from the skins and the stems and pulp of the grapes. It may be slightly 

 cloudy or nearly clear. It can then be drawn off into clean casks and fermen- 

 tation started with yeast. The microorganisms settle only in part but they are 

 all paralyzed temporarily. 



This defecation is of great value, ridding the must of substances that would 

 affect the flavor of the wine in the heat of fermentation and eliminating the excess 



* Formerly a decision of the U. S. Dept. of Agriculture forbade the use of the term "pare 

 wine" when water in even the smallest quantities had been used. By the federal law of 1916 

 dilution with water up to 35 per cent, is allowed. 



