The pH or the acidity of wine affects many stages in wine making and ageing. The fruits which are usually used for wine making are acidic by nature, but sometimes as a practice wine makers add some acids to enhance the qualities of wine and aid the ageing process.
A low pH value will inhibit the growth of bacteria and it can also inhibit the yeast growth upto a certain level. It increases the desirable flavour compound production and inhibit the production of undesirable compounds.
Also pH level affects the taste of wine. If pH goes below 3.0 wine will have a more tart taste and when pH is around at 4 wine is known to has a flat taste. Therefore adjusting of pH in wine making is quite important, but the ability to adjust pH and produce a great wine come only through practice and tradition.