Also known as malic acid or hydroxysuccinic acid, it is one of the three most important organic acids in wine, along with tartaric acid and citric acid. In nature, it occurs mainly in unripe apples, barberry berries, quinces, gooseberries, rowan berries and grapes. It got its name because it was first isolated and described from apple juice in 1785. In the still unripe grapes it has a high content of up to 20 g/l, in the wine the content is between 0.5 and 6 g/l. Parallel to the sugar storage during berry ripening, the must acids decrease.
Malic acid is metabolised between 20 and 30 °C, i.e. it is burnt off in the course of cell metabolism and converted into sugar, whereas the degradation of tartaric acid only takes place at higher temperatures. This is why the remaining proportion of tartaric acid is always higher in ripe grapes. Tartaric acid is considered to be a soft, pleasant acid, whereas malic acid is considered to be a more aggressive-tasting acid that makes wine taste edgy and hard.