Do you need to adjust the acid levels in your wine? Do you need to lower the pH of your fermentation must?
Both of these can be accomplished using Tartaric Acid. It will also work as a preservative after fermentation is complete. It can also provide some of the tartness that you would expect in a wine. It is the most widely used acid for winemaking.
Typical usage is 1 tsp per gallon in order to increase the acidity by 0.1% per gallon.
It can also be used in your Ciders for post MLF adjustments.