it's (fairly) easy to read a recipe that's already out there, or use a kit that someone else has already pre-packaged all the ingredients. but i would like to take it to the next step and be able to calculate the correct proportions myself.
if i have a grape, how can i figure out its sugar content? how do you know the correct proportions of sugar/liquid/yeast? how do you know when to move to secondary (tertiary) fermentation? if you alter those lengths, how will that alter the end product and which characteristics will be altered?