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Importers of Fine Wines Since 1919 | Resources for the Trade |
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Making it soft and suppleWine is a distinctly acidic beverage. In fact, some wine makers feel that it can be a little too tart! In such instances, they put the wine through a second fermentation in order to change the nature of the acids in the wine. This results in a softer, creamier finished product. 
The technique is known as malolactic fermentation. In this process, malic acid is converted into lactic acid. Although this is an acid to acid exchange, the nature and the strengths of the two acids are quite different. Malic acid is tart, sharp and tastes of green apples. Lactic acid is softer and tastes of butter, butterscotch, toffee and caramel. These flavors are reflected in the finished wines! The hard, tart factsThe number one acid in wine, both in strength and in concentration, is tartaric acid. Before bottling, a winemaker will chill a wine in order to precipitate out some of this tartaric acid. (As you may remember from chemistry class, the solubility of a substance decreases with temperature!)
Sometimes, you’ll even find them in the bottom of your wine bottle, but they are harmless! You see, some producers feel that any time they handle a wine, they diminish its flavor, so they prefer to run the risk of tartrates in the bottle vs. adding another step to the winemaking process 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10
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Unlike the alcoholic fermentation which was carried out by yeasts, the malolactic fermentation is performed by bacteria. Malolactic fermentation is executed by the same bacteria that separate curds from whey in cheese making!
Lees are the dead yeast cells that collect at the bottom of the barrel or vat after the primary alcoholic fermentation is complete. Sur lie, in French, means “on top of the lees.” A wine that has gone through malolactic fermentation will pick up flavors of butterscotch, toffee, butter and caramel. Tartaric acid has a harsh taste that many compare to baby aspirin.
Tartrate crystals are called “Weinsteine” in German (wine stones). The Germans view them as a sign of quality. 
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The tartaric acid precipitates out as crystals called tartrates and settle to the bottom of the tank or vat then they are removed. Sometimes these crystals look like snowflakes; at other times, like shards of glass or bits of rock candy.
White wines that undergo malolactic fermentation often spend time resting on their lees in a process known as “sur lie aging”.
Tartrates are harmless. In fact, you know them well. Tartrates are sold as ‘cream of tartar’ in the baking aisle of your supermarket. You add a pinch to get those egg whites stiff!