Malic acid is the acid found in apples and is, therefore, the best choice for adjusting ciders.
A rough approximate of weight is 1 tsp = 2.7 grams.
One level teaspoon of Malic Acid will raise the acid content of on U.S. gallon by .15%-tartaric.
Product of Europe
Malic is less sour than tartaric acid and can also be used to make acid adjustments in Rieslings, Gewurztraminer, and Muscat varieties, though many winemakers still prefer to use tartaric acid in these situations. You would not want to add Malic acid to any wine that will undergo malolactic fermentation. As a note: only half of the artificially added malic acid will convert to lactic acid during malolactic fermentation.