428 MICROBIOLOGY OF SPECIAL INDUSTRIES. 



the fumes of burning sulphur or with a solution of potassium metabisulphite is there- 

 fore 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 impuri- 

 ties including microorganisms, dust and solid particles derived 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 fermentation started with yeast. 



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 of protein 

 matters that would serve as food for injurious bacteria. Centrifugal machines have 

 been devised to hasten the process of defecation, but their work is less perfect. 



Sterilization by heat has been tried for the same purpose but with indifferent 

 success. High heating caramelizes part of the sugar and oxydizes the must, thus 

 injuring the flavor. Discontinuous heating at lower temperatures in an atmosphere of 

 carbon dioxide is preferable but troublesome and expensive; all methods have the 

 defect of extracting undesirable substances from the solid matters which are heated with 

 the must. 



Chemical sterilization is still less practicable. No substance could be used for 

 this purpose except sulphur dioxide; this used in sufficient quantities would seriously 

 injure the flavor of the wine. The effect would be totally different from that of the 

 small quantities used in defecation. 



All the methods discussed have for their object the diminution or elimination of 

 microorganisms of all kinds. With the injurious forms the true yeast is also removed. 

 The more perfect these methods, the more necessary it is to add wine yeast. Without 

 this addition, in fact, all these precautions may result in harm, for the wine yeast, being 

 present in much smaller numbers than many of the injurious forms, may be completely 

 removed while enough of other forms are left to spoil the wine. 



A " starter" of some kind is therefore necessary with defecated must 

 and useful in all other cases. 



A Starter. One method of producing such a starter is to gather a suitable quantity 

 of the cleanest and soundest ripe grapes in the vineyard, crush them carefully and allow 

 them to undergo spontaneous fermentation. Perfectly ripe grapes should be selected 

 and the fermentation allowed to proceed until at least 10 per cent of alcohol is pro- 

 duced. If imperfectly ripened grapes are used or the starter used too soon, the 

 principal yeast present will be S. apiculatus. Toward the end of the fermentation, 6*. 

 ellipsoideus pre-dominates. From 4 to 12 1. (i to 3 gallons) of this starter should be 

 used for each 500 1. (100 gallons) of grapes or must to be fermented. Too much 

 "starter" should not be used in hot weather or with warm grapes; unless this precau- 

 tion is obesrved, it may be impossible to control the temperature. 



This starter is used only for the first vat or cask. Those following are started 

 from the first fermentations, care being taken always to use the must only from a 

 tank at the proper stage of fermentation and to avoid all tanks that show any defect. 



An improvement on a natural starter of this kind is a pure culture of tested yeast. 



