Brewing beer require an understanding of how yeast converts sugar into alcohol. Understanding how yeast converts sugar into alcohol allow a person to understand how much alcohol will be contained in your beverage when it is complete. Yeast performs the conversion of sugar into alcohol, but it doesnt completely convert all of the the sugar to alcohol.
Instead, half of the weight of the sugar is converted to ethanol, and half of the weight of the sugar is converted to carbon dioxide with the remainder of the sugar being used to perform the growth of the yeast. Consequently, because some of the sugar from a specific weight of sugar is converted to carbon dioxide, only a specific and predictable amount of that sugar will become alcohol in the final product. The type of sugar that is used will change the amount of alcohol that is produced due to the difference in fermentable material within the different type of sugars.
How Yeast Turns Sugar into Alcohol
If using table sugar, which is pure sucrose, the yield of alcohol will be high from that sugar. Using honey, which contains some non-fermentable material, will lead to slightly lower yields of alcohol. Brown sugar contains molasses, which adds flavor to the brew but reduces the amount of alcohol that is produced due to the high amount of non-fermentable material within the molasses.
A chart can be used to display the difference in these yields to allow for the substitution of one type of sugar for another. Temperature will impact how the yeast perform the conversion of sugar to alcohol. If the temperature is too low, the yeast will not effectively perform the necessary chemical reaction to produce alcohol, leading to lower alcohol levels in the completed batch.
The ideal temperature for brewing is between sixty-five and seventy-five degree. If the temperature of the brew is too high, over eighty-five degrees, the yeast will begin to suffer, leading to the production of off-flavors in the beer. By controlling the temperature at which the brewing process occurs, the yeast can effectively perform its conversion of sugar to alcohol.
The type of yeast that is used will impact the amount of alcohol that can be produced due to the different alcohol tolerances of each type of yeast strain. Bread yeast has the lowest alcohol tolerance of the yeasts, only able to ferment to around 8%. Ale yeasts can ferment to around 11% alcohol, but wine and champagne yeasts can reach alcohol percentage in the mid-teens.
Distiller yeasts are capable of producing alcohol levels above 20% if the brewing conditions is set accordingly. Matching the type of yeast to the amount of sugar in the batch will ensure that the yeast can survive the fermentation process. To calculate the percentage of alcohol in the final product, the difference between the original gravity of the batch and the final gravity can be used.
The brewer must measure the original gravity prior to the addition of the yeast and the final gravity is measured after the batch has fermented. Multiplying the difference between these two gravities produce a constant that can be used to calculate the percentage of alcohol in the beer. A chart can be used to display the alcohol yields from different amounts of added sugar to the batch to allow the brewer to understand if the desired percentage of alcohol is achievable with there batch.
The batch size does not change the relationship between the amount of sugar in the batch and the amount of alcohol create. However, batch size do change the amount of sugar that is used. The relationship between gravity points, pounds of sugar, and gallons of liquid is the same regardless of batch size.
By knowing the amount of sugar needed to reach a certain amount of alcohol, the brewer can adjust the batch size without having to change the recipe altogether. By tracking the relationship between batch size and the amount of sugar needed, brewing becomes a scientific process with no guesswork. By also tracking these relationships, it becomes possible to adjust only one variable at a time to understand the reason for the changes in the batch.