Malic acid: a grape acid, not a fault

The standard

As a microbially degradable acid, malic acid is the target of malolactic fermentation: its level decides how much acidity a wine loses through this breakdown and how much softer it becomes.

Criteria

• It is distinguished from microbially stable tartaric acid as an acid of its own
• Its level falls with grape ripeness, not with ageing
• It is the substance that biological acid conversion transforms

Distinction

Malic acid ≠ tartaric acid: both are grape acids, yet tartaric acid stays microbially stable while a microbially degradable acid is removed by lactic-acid bacteria. Malic acid ≠ lactic acid: the one is the starting substance of biological acid conversion, the other its result.