+ 1 on salcoco's post..
there are limits on PH, SO2 and ABV levels.
Malic acid is a harsh form of acid (much like that found in a grapefruit).
Lactic acid is a softer form of acid that can be found in milk.
Like Salcoco said above, Malolactic fermentation converts malic acid to lactic acid.
You may hear of a wine tasting buttery and soft? Most of the time this is due to a malolactic fermentation.