Must is grape juice (sometimes still mixed in with the peels) before or at the start of fermentation, just as wort is malty sugary water but becomes beer when y

Must is grape juice (sometimes still mixed in with the peels) before or at the start of fermentation, just as wort is malty sugary water but becomes beer when yeast is added and fermentation begins. At the end of fermentation very little sugar remains, so these are definitely not interchangeable liquids. These terms have a legal definition in most places, because wine and beer is taxed heavily but grape juice is not.