Winemakers Influence on Acidity
How Winemakers Adjust Wine Acidity
Winemakers regulate acidity during and after fermentation. Keeping the acidity of a wine within varietal specific ranges has very important benefits and allows the wine to reach its full potential. Acidity affects all aspects of the wine, from taste and feel, to color and stability, to microbial resistance.
Winemakers can regulate and influence the acidity in their wines by:
- Cold Stabilization: Reduces total acidity by reducing tartaric acid.
- Malolactic Fermentation: Reduces malic acid, which tends to be harsh, changing it to lactic acid, which is much softer.
- Adding Citric Acid: Balances malic acid dominated fruit base.
- Adding Tartaric Acid: Usually added to a wine with low acidity.
- Adding Acidic Blend: To round out a wine with low acidity.
Lowering the Acidity of Wine
Winemakers can lower the acidity of their wines in a variety of ways:
Cold Stabilization Techniques: Acid levels can also be reduced by cooling the wine to the point that tartrate crystals are formed. This means that the tartaric acid will react with other molecules to form a solid, which is then purged from the wine. Different chemicals can also be added that will remove tartaric acid from a wine. Winemakers exercise caution in this process, because wines with low acidity tend to taste “fat.”
Adding calcium carbonate: Calcium carbonate primarily reacts with tartaric acid and is relatively inert in the presence of malic acid. However, a by product of this reaction is calcium malate, which is a solid precipitate from a small amount of malic acid reacting with calcium carbonate. Cold Stabilization should follow this procedure to ensure that all of the tartrate crystals are removed before bottling.
Adding potassium bicarbonate: This molecule is a buffer that is used to de-acidify wine with too much acid. A 30% reduction in total acidity can be seen in this procedure and should be followed by Cold Stabilization.
Adding potassium bitartrate: Potassium bitartrate is used to promote cold stabilization. The mechanism of action lies in the principles of equilibrium; adding this will shift the reaction to promote formation of tartate crystals from tartaric acid, reducing the acidity of the wine.
Malolactic Fermentation: Alcoholic Fermentation refers to the process were yeast consumes sugars and produces alcohol and carbon dioxide. Malolactic fermentation is quite different; Leuconostoc bacteria cultures, not yeast, are introduced during or following alcoholic fermentation. These bacteria convert tart malic acid into softer lactic acid, reducing perceived acidity and leaving a rounder profile.
Raising the Acidity of Wine
Keeping wine at an acidic pH is very important for the wine. In some cases, it is wise for the winemaker to add acid to raise the acidity to the levels necessary to maintain its qualities.
Adding Tartaric Acid: If the acidity is too low, winemaker will often add tartaric acid. Tartaric acid has numerous benefits, including a high Ka (which is a measure of the strength of the acid: the higher the more acidic) and microbial stability. However, it does have its disadvantages; the main being tartrate crystals forming on cork. Many see these crystals as a sign of spoilage, but this is a natural process that does not affect the quality of the wine.
Adding Citric Acid: Citric acid is a less common way for winemakers to increase the acidity of their wine. But it does have its benefits, one of them being that it does not form tartrate crystals. The main disadvantage is that it is easily metabolized by bacteria, making it microbially unstable. However, cirtic acid adds a crisp freshness to a wine that tartaric acid does not.
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