CHAPTER VI.* 



THE MICROBIOLOGY OF ALCOHOL PRODUCTS. 



WINE. 



Wine may be defined shortly as the product of the alcoholic fermenta- 

 tion of grapes and the usual cellar treatment. 



The classifications of wines are numerous and the varieties innumerable. They 

 may be separated, however, into a few main groups, depending on chemical composition 

 and methods of manufacture. Dry wines are those in which practically all the sugar 

 has been removed by fermentation; sweet wines, those in which enough sugar remains 

 or is added to be noticeable to the taste; fortified wines, those that have received an 

 addition of distilled wine spirits; and sparkling wines, those highly charged with carbon 

 dioxide, produced by supplementary fermentation in the bottle. Each of these 

 groups includes white wines made from the expressed juice of the grape, and red wines 

 made from both the juice and skins of red grapes. 



GRAPE JUICE AND WINE AS CULTURE MEDIA. 

 Grape juice, known technically as must, is a sugary, acid, organic so- 

 lution very favorable to the growth of yeasts and of many other fungi, 

 but unfavorable to most bacteria. Wine is of a similar composition but 

 contains alcohol instead of sugar and is therefore less favorable to the 

 growth of most microorganisms. Both liquids are of highly complex 

 composition. Their character as culture media is indicated by the fol- 

 lowing table: 



Composition of Must and Dry Wine. 



Must. 



Wine. 



Specific gravity 



Fermentable Sugar . 

 Alcohol by volume. . . 

 Acidity (as Tartaric) . 

 Nitrogenous matters 

 (soluble) 



Tannin 



Dry extract 



Ash. 



i. 0600 to 1. 1090 

 12. o to 25.0 per cent 

 none 



.5 to i. 25 per cent 



.2 



Traces 



to . 4 per cent 



.20 to .70 per cent 



. 9850 to i . oooo 



o to . 5 per cent 

 8.0 to 15.0 per cent 

 .25 to i. o per cent 



variable but small 

 traces to .30 per cent 

 .15 to .40 per cen 

 .13 to . 50 per cent 



* Prepared by F. T. Bioletti. 



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