Malic acid is used to lower the pH of a wine or cider, however if your going to have your wine or cider go through a Malolactic Fermentation (MLF) you should not use Malic Acid.
Malic acid is less sour than tartaric acid and can therefore be used in Rieslings, Gewurztraminer, and Muscat varieties. It will adjust the acidity by 0.1% per gallon.
It can also be used in adjusting Cider pH's since Malic acid is the acid primarily found in apples.
Usage: 3.4 grams per gallon