SI? MICROBIOLOGY OF SPECIAL INDUSTRIES 



During Fermentation. — However carefully the injurious germs 

 have been excluded and the good yeast increased, fermentation will not 

 be successful unless conditions as favorable to the latter and unfavorable 

 to the former as possible are maintained. 



The temperature of the crushed grapes or expressed must is of 

 importance. If it is below 15°, unless the weather is warm, the grapes 

 should be warmed to 20° or 25°. Unless this is done, the molds and 

 S. apiculatus, which require less heat than S. dlipsoideus, will develop 

 more quickly. This is especially true when starters are not used. In 

 the warmer and earlier districts the grapes are practically never too 

 cold. On the other hand, unless there is great carelessness, the grapes 

 are never too warm for the commencement of fermentation. The 

 warmer they are, however, the more artificial cooling will be necessary 

 later, and the sooner it will have to be applied. 



Thorough crushing is necessary in the case of white wine, to faciU- 

 tate the expression of the juice. For red wine, the grapes are also 

 thoroughly crushed and the skin, pulp and juice are fermented together. 

 Imperfectly crushed grapes ferment unevenly and incompletely; thus 

 the growth of mold is much facilitated. 



The must should be thoroughly saturated with air at the beginning 

 of fermentation to insure the multiplication of the yeast. The aeration 

 received in the processes of stemming, crushing and pressing is usually 

 suflScient for this purpose. More aeration would be harmful by injur- 

 ing the flavor and color of the wine by over-oxidation and promoting 

 the growth of injurious aerobic organisms. An objection to the sterili- 

 zation of must by heat is the expulsion of the air and the difficulty of 

 replacing /it in the proper amount. 



The proper use of sulphurous acid in the regulation of fermentation 

 is one of the most important and necessary but least understopd parts 

 of the wine-maker's art. Only by this proper use can wholesome 

 wine of the highest quality be produced. Improper use will injure or 

 completely spoil the wipe. Its beneficial effects are due primarily to 

 its action on microorganisms, on enzymes and on the color of the wine. 



In the small quantities properly used in winemaking, it is antiseptic in a degree 

 varying with the amount. All microorganisms are susceptible to its action in vary- 

 ing degrees. Bacteria are particularly sensitive, molds and psuedo-yeasts less so, 

 while wine yeast is the most resistant of the ordinary forms found in must and wine. 



The result of the use of the proper amount of sulphurous acid in crushed grapes 



