Geronimo
Norges Skaal!
- Joined
- Nov 19, 2011
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When first pouring the must into a fermenter, the resulting splashing and foaming oxygenates the mixture. When you inoculate the must with yeast, since there is a presence of O2, the yeast will immediately set to work multiplying and growing until they have consumed all the O2. During this aerobic phase (and continuously until the end of the fermentation) yeast will produce mainly CO2 gas and ethyl alcohol, along with some hydrogen, methane, and various other things. CO2 is heavier than air, therefore right after fermentation starts the must will have a blanket of CO2 over it unless it is purposely disturbed by air movement. Even with air movement, the oxygenation of the must after fermentation starts is very minimal unless the must is vigorously agitated which can harm the yeast and oxidize the fermentation.
Once all the O2 is consumed in the must, anaerobic fermentation continues until all nutrients and sugars are consumed. During this phase, the introduction of O2 is typically harmful and can cause premature spoilage, bacterial infections, etc. It is always best to limit the exposure the wine has to O2 from this point and through the bottling process. Even in the bottle, only a small amount of air is left in the headspace. Also, the fermentation should conclude with all available yeast cells to ensure a clean fermentation that does not stop prematurely, and that keeps competing organisms in check. Removing the yeast cake from the bottom of the vessel, or skimming the yeast foam or krausen from the top in mid-fermentation is not advisable. In fact once fermentation appears to be complete, leaving the wine in contact with all available yeast for 2-4 weeks will produce the cleanest, most completely fermented final product.
So in conclusion, you should aerate the must before inoculating with yeast, pitch a healthy yeast dosage and some nutrient, then leave the yeast to do the rest without intervention. Managing the temperature and sanitation throughout these phases is the best practice that will help you end up with the desired final product.
Once all the O2 is consumed in the must, anaerobic fermentation continues until all nutrients and sugars are consumed. During this phase, the introduction of O2 is typically harmful and can cause premature spoilage, bacterial infections, etc. It is always best to limit the exposure the wine has to O2 from this point and through the bottling process. Even in the bottle, only a small amount of air is left in the headspace. Also, the fermentation should conclude with all available yeast cells to ensure a clean fermentation that does not stop prematurely, and that keeps competing organisms in check. Removing the yeast cake from the bottom of the vessel, or skimming the yeast foam or krausen from the top in mid-fermentation is not advisable. In fact once fermentation appears to be complete, leaving the wine in contact with all available yeast for 2-4 weeks will produce the cleanest, most completely fermented final product.
So in conclusion, you should aerate the must before inoculating with yeast, pitch a healthy yeast dosage and some nutrient, then leave the yeast to do the rest without intervention. Managing the temperature and sanitation throughout these phases is the best practice that will help you end up with the desired final product.