Potential Alcohol

The fermentation equation:
C6H12O6 -> 2 C2H5OH + 2 CO2
Fermentation converts sugar into alcohol and carbon dioxide. In my last post, I talked CO2, so I’m going to focus a little more on the creation of alcohol in this post.

The yeast will eat sugar, fructose, corn sugar, or honey to create alcohol. These types of sugars, when added to water, make water become thicker. There is a device called a hydrometer that can be placed in the solution. The thicker the solution, the more the hydrometer rises, and it sinks the thinner the solution is. Water will measure in at 1.000, and a finished dry wine will be a little less than that. This measurement is called Specific Gravity, often noted as SG.

So at the beginning, before yeast is added to the batch, a sample is taken in which the sugar content is found with an SG measurement. There are tables that then say for a given SG at a particular temperature, the yeast’s potential to convert sugar to alcohol will be x amount. This is important because it allows the brewer to know how strong of a drink it will become.

Further tests can be taken to know when the drink is done fermenting, as there will be no more sugar remaining. Also, sometimes the yeast quit working for a little bit, at which point it is “stuck”. Doing the test allows the brewer to recognize this problem and modify it.