The total acidity, calculated as tartaric acid, may vary from as low as 0.3 to as high as 1.5 per cent. The amount varies with the season and variety. Tartaric acid does not appear to be formed from malic acid. Rather it appears to be a by-product of photosynthesis with carbon atoms 2 and 3 of Tartaric acid being the same as atoms 3 and 4 of dextrose. So far as is know tartaric acid is not a part of Krebs cycle.