Sunday, October 25, 2009

"A" is for Acidity

Some wine lovers have difficulty distinguishing and understanding the difference between acidity and tannin in wine. These are technical wine terms. Acidity is experienced on the palate as sourness, tanginess or zestiness. Tannin and astringency are experienced as bitterness and dryness.

If you bite into a lemon (acidity) and then chew a walnut (tannin), you will understand the difference between these two taste sensations. Both sensations are important to the taste, quality and longevity of wine.

Wine has three primary acids -- tartaric, malic and lactic. Acidity provides the refreshing bite we experience when we wip, supports the fruit flavours and adds to the after taste in the wine. Acidity also helps wine retain its colour and preserves its lifespan. A wine with good acidity will last for a longer time in the wine cellar. A wine with too much acidity can taste sour. This sourness is often misinterpreted as bitterness. A wine with too low acidity will taste flat. Tartaric acid accounts for more than half the total acidity in wines produced in warm climates. Some precipitates as an acid salt called potassium bitartrate or cream of tarter during the winemaking process. At home when the wine is chilled, the cold forces more potassium bitartrate to fall to the bottom of the bottle and form crystals. The crystals tell us that the wine was produced from ripe grapes that had sufficient acidity and minerals. The crystals, often referred to as wine diamonds or wine stones, are tasteless and colourless. Wine possessing crystals should be decanted.

Malic acid is the most sour of acids. It gives wine that distinct green-apple taste and is more readily found in wines produced in cooler climates. During the winemaking process, the winemaker will reduce this acidity by putting the wine through a malo-lactic fermentation. This secondary fermentation transforms some of the malic acid to lactic acid, thereby giving the wine a softer taste and creamy mouth feel.

Tannin comes from the stems, seeds and skin of the grapes during fermentation and from the oak barrels used to ferment and/or age wine. The level of tannin and astringency in the wine is determined by the grape variety used, the length of time the juice remains in contact with the skin/stems during fermentation and the time the wine spends in oak barrels. Some red grape varieties like pinot noir are thin skinned and so do not impart much depth of colour to a wine. As a result pinot noir is mostly light red with soft tannin and refreshing acidity. Cabernet sauvignon has thicker skin. As a result the wines are concentrated in colour and have a good dose of tannin. The use of oak barrels for fermenting and aging contribute to the level of tannin in white and red wine, as well. French oak barrels impart more tannin to wine than American and Eastern European barrels. Like acidity, tannin and astringency is also a preservative contributing to a wine's longevity.

Try the lemon and walnut test, then sip from a glass of cabernet sauvignon. You should be able to detect both the acidity and tannin in the wine.

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