It really isn’t important that you learn a lot about wine and beer making through the fermentation of yeast. It’s a simple process. You really need to know only a few things to make good wine and beer.
Wine and beer making through yeast fermentation is a chemical process by which microorganisms such as bacteria, molds, and yeast break down sugars into water, alcohol, and carbon dioxide gas.
The Yeast Fermentation Process
Yeast fermentation has been around for a very long time. Often, when a person begins to research the fermentation process, they are not aware of the fact that this has been going on almost since all of recorded history. The idea of wine and beer making through yeast fermentation is something that has been going on for many many years, this is part of why it is so important to find out your information from the sources that can actually help you.
Normal Home Brewing Fermentation Process Is In Two Parts. Part 1 Aerobic (Oxygen is present) This is the initial rapid process where the yeast is doubling its colony size every 4 hours. (Usually 24-48 hours) Part 2 Anaerobic. (No oxygen present) Slower activity and the yeast focuses on converting sugar to alcohol rather that increasing the number of yeast cells. (This process can take from days to weeks depending on the yeast and the recipe)
Fermentation Basics How It Works
When yeast is used to ferment a solution containing a lot of sugar, fermentation usually stops although sugar and yeast are still present.
Yeast have evolved what some consider a "primitive" form of metabolism to use sugar for an energy source. In alcohol fermentation, yeasts that produce carbon dioxide and alcohol and energy as end products, when the alcohol reaches a certain level it will inhibit the yeast from fermenting any more sugar.
Yeast cells ferment sugar because they can! When there is no Oxygen available, only organism that can ferment are able to synthesize and reproduce. The alcohol and CO2 increase in fermentation, eventually this inhibits the cells even though there is still sugar available.
The level of alcohol tolerance by yeast varies from 5% to about 21% depending on yeast strain.
Brewer's yeast can tolerate up to about 5% alcohol. Anything beyond this alcohol level the yeast cannot continue the fermentation process. Wine yeast on the other hand tolerates up to about 12% alcohol.
The fermentation process has other limits such as temperature. Greater than 27C kills the yeast less and than 15C results in yeast activity which is too slow. The amount of sugar in the solution can be too high and this can prevent fermentation. Some recipes suggest adding the sugar in parts throughout fermentation rather that all at the beginning. This is especially true if the brew is aimed at producing a high level of alcohol. Some yeast strains have evolved to handle higher sugar levels. Yeast such as Tokay and Sauterne.
To learn more about the role of fermentation in human history, read Brewing for Millenia
