The principle of wine making is that in the process of wine making, the sugar in the grapes is converted into alcohol and carbon dioxide by the action of the yeast, thus turning into wine.

And generally homebrewed wine is made from table grapes, which do not have as high a sugar content as specialized wine grapes, so sugar is added, and the purpose of adding sugar is to achieve a reasonable alcohol content.

Purpose of adding sugar:

During the wine fermentation process, sugar is added not to achieve sweetness, but to obtain the target alcoholic strength, the principle is roughly as follows:

(1) It is broken down into glucose and fructose under the action of sucrose converting enzyme.

(2) Glucose and fructose, converted to alcohol, carbon dioxide, and water by the action of yeast.

Therefore, sugar is added only if the original sugar in the grapes is too low, and the amount of sugar added is also directly and positively correlated with the original sugar level and the target wine level.