604 



MICROBIOLOGY OF ALCOHOLIC FERMENTATION 



growth of most microorganisms. Both liquids are of highly complex 

 composition. Their character as culture media is indicated by the 

 following table: 



COMPOSITION OF MUST AND DRY WINE 



Must 



Wine 



Specific gravity , 



i. 0600 to 1.1090 



Fermentable sugar 12.0 to 25.0 per cent 



Alcohol by volume 



Acidity (as tartaric) 



Nitrogenous matters 



(soluble) 



Tannin 



Dry extract 



Ash., 



none 

 o-5 



O. 2 



Traces 



to 1.25 per cent 

 to 0.4 per cent 



0.20 to 0.70 per cent 



o . 9850 to i . oooo 

 o to o . 5 per cent 

 8.0 to 15.0 per cent 

 0.35 to i.o per cent 



variable but small 

 traces to 0.30 per cent 

 1.4 to 4 . o per cent 

 0.13 to 0.50 per cent 



Fortified wines (sweet wines are usually fortified) usually con- 

 tain enough alcohol to make them practically antiseptic to all 

 microorganisms. 



THE MICROORGANISMS FOUND ON GRAPES 



On the surfaces of grapes, as they are brought to the cellar, may be 

 found any of the bacteria and fungi usually carried by the air and by 

 insects. Many of these are incapable of growing in grape must, and 

 are, therefore, without effect on the wine. 



MOLDS. The spores of the common saprophytic molds, Penicil- 

 lium, Dematium, Aspergillus, Mucor, are always present in abundance, 

 and they find in must excellent conditions for development. Botrytis 

 cinerea, a facultative parasite of the leaves and fruit of the vine, is also 

 nearly always present in larger or smaller quantities. All these molds 

 are harmful to the grapes and the wine. Some of them, such as Penicil- 

 lium, may give a disagreeable, moldy taste to the wine, sufficient to 

 spoil its commercial value. Others, such as some Mucor s and Asper- 

 gilli, may injure the wine but slightly except by destroying sugar and 

 diminishing the alcohol. Dematium pullulans may produce a slimy 

 condition in weak white musts and most of them may injure the 

 brightness and flavor to some extent. 



On sound ripe grapes these molds occur in comparatively small 

 numbers and being in the spore or dormant condition they are unable 



