Acids represent an important part of wine constituents and help preserve it. They are members of chemical compounds responsible for the sharp or sour tastes of all drinks and foods.
There exist several acids in wines, the most important of which are tartaric, citric, malic, lactic, succinic, and acetic.
Grapes contain a large of acids other than those mentioned above, but their importance is limited.
On average, wine contains 5 – 8 and occasionally more grams/litre acids. Low acid wines taste “flat”, fail to refresh or cleanse the palate, and do not allow the wine to cellar well.
An acid is a compound that yields hydrogen ions or protons (H+) in solution, or reacts with alkalis to form salts.
Acidity is also measured in pH values.
The scale contains 14 grades or levels. Level 7 is neutral, below 7 all grades are acids, and above alkaline.
The pH value of a solution indicates its concentration of hydrogen ions. A wine with a low pH value cellars well.
Grape, pending on climate may be high or low in acidity, and those from cool regions, high. Generally, grapes grown in warm climes are low in acidity. Winemakers can and do adjust acid levels in wine by chemical additions – in Jerez de la Frontera, where sherry wines originate, calcium sulphate (CaSO4) is added to compensate for lack of acidity.
Citric acid (C6H8o&) is added after fermentation to prevent haze in sparkling wines in Canada.
Tartaric acid (C4H6O6) is the most common acidulant in many regions.
Malic acid, found in considerable amounts in apples, occurs naturally in cool climate wines ad can be mellowed by subjecting the wine to a malolactic fermentation whereby half of the malic acid is converted to “soft” lactic acid commonly found in milk. The Ml (as it is called by winemakers) is initiated by increasing the cellar temperature by a few degrees as is done in Beaujolais nouveau production.
In Germany and other countries, the ml is left up to nature. In spring when temperatures increase naturally the process starts spontaneously.
Acetic acid occurs when fermenting juice or wine is exposed to excessive amounts of oxygen. Acetic acid in wine is highly undesirable.
In cool climate regions, winemakers de-acidify wines to reduce tartaric acid by addition of water, or blending, or fermenting using acid-reducing yeasts, or employing the ml process.
Potassium bicarbonate (KHCo3) or potassium carbonate (K2CO3) or calcium carbonate (CaCO3)
may be employed for minor de-acidification.
In adequate quantities acids make for a refreshing, cleansing, and balancing flavour. They uplift the taste of the wine.
Entry-level wines are generally low in acidity, don’t cellar well and generally considered to be insipid. Refined wines contain by contain a certain level of acidity for balance, and are sought by connoisseurs.
In practically all cool climate wine producing regions winemakers leave a small amount of residual sugar in their wines to balance for high acidity, or use the sussreserve technique, invented by German winemakers.