About half a gram of citric acid per gallon is often added to commercial wines to improve long term stability. Diammonium phosphate is a major ingredient in many proprietary yeast foods. It is added to juice or must before fermentation to supply extra nitrogen. The additional nitrogen encourages rapid yeast growth and more dependable fermentations. California Chardonnay grapes are often deficient in nitrogen, and many winemakers add DAP to all Chardonnay juices to help the yeast complete fermentation and not leave residual sugar in the wine.
Juices lacking nitrogen can cause another problem.
Some yeasts produce excessive quantities of hydrogen sulfide when a juice lacks sufficient available nitrogen. Here, winemakers add DAP to provide extra nitrogen to reduce hydrogen sulfide formation. In the past, winemakers often added small quantities of fumaric acid to their red wines. The acid prevented malolactic fermentation from occurring after the wine was bottled. However, since sterile filtration equipment became widely available, fumaric acid is seldom used commercially.