A wine which doesn’t have enough acidity is flabby and boring.
What is acid?
It is one of the five primary tastes – sweet, sour (acid), bitter, salt and umami (savoury). An example of an acid is citric acid in lemons. These tastes are detected by tastebuds, which are located mainly on the tongue, but also in other parts of the mouth.
How acid levels change as a grape berry grows
The diagram above shows that acid levels increase as a grape berry grows, but only to a point. Véraison is the moment when a grape berry changes, and starts to ripen; it softens, changes colour, sugar levels rise, and acid levels fall. Unripe grapes are hard and acidic, with little sugar. Over-ripe grapes are sweet and bland.
Which acids are present in wine?
Tartaric is the main acid, and its level stays fairly steady during ripening. Malic acid is the other significant acid, and this decreases after véraison.
Examples of two contrasting types of wine:-
- Champagne – the grapes are picked with high acidity, and quite low sugar levels. In most wine regions the grapes would be considered under-ripe. At the end of production, sugar is usually added to take the edge off the acidity.
- High alcohol Cabernet Sauvignon – these come from hot climates, where the grapes are picked very ripe, with high sugar levels and relatively low acidity. This sugar produces a wine with plenty of alcohol, and acid may be added to make the wine more palatable.
How can you tell how much acid is in a wine?
Unfortunately, very few wine labels provide this information, but the winemaker’s website often does. Acidity is usually stated as pH. I won’t bore you with a chemist’s definition, but pH is a scale in which water is neutral at level 7. The lower the number, the more acidic a liquid is, and wine is usually 3 to 3.5.
A balancing act
Acidity is particularly important in sweet wines, to ensure they are not bland. Sugar masks the acidity, so it may not be obvious, but all good sweet wines have it.