Two years later, they realised the fermentation is caused by bacteria, not yeasts, as with alcoholic fermentation. In 1900 malolactic bacteria were isolated for the first time, and injected into a wine to induce a malolactic fermentation, and in 1901, the chemical equation was put to paper. As a grape ripens, its sugar level increases and its acidity, or pH level, decreases. Winemakers must decide at what point they decide to harvest depending on the style of wine they are making. While the ability to age cannot be reduced to just one variable, generally speaking if the wine is one to enjoy early, the grapes will most likely have a lower acid content than those used for a wine destined for ageing.
Acidity is also important in terms of structure.
A wine with too much acidity, however, comes across as too sharp. Yves commented that almost all red wines undergo malolactic fermentation, partly to exhibit these characteristics, and partly to stabilise the wines. For white wines, there is more choice. If a wine is made in a cool climate region, the grapes naturally have a higher amount of acidity than those coming from a warm region. Cool climate wines often need softer acidity, and malolactic fermentation is quite frequent.