How do they know how much alcohol the beverages contains when companies make alcoholic beverages?

Question

For example how do they know/measure that a beer contains 4.5% alcohol?

In: 3

Answer 1

Alcohol is made by the fermentation of sugar by yeast. Essentially the yeast eats the sugar and poops out alcohol.

A solution of water and sugar is more dense than a solution of water and alcohol. So the way that you figure out how much alcohol was made is by taking the density of the product before fermentation has started, and the density of the product after fermentation is complete. Then you use a formula that computes the difference in density into alcohol percentage.

People who make wine and beer at home do this with a device called a hydrometer, which is a glass bulb that kind of looks like a thermometer. You fill a test tube with your liquid and you float the hydrometer in it, and based on how high it floats, that tells you the density of the liquid.