Chapter 19

Juice and Wine Acidity

Deacidification of Must and Wine

Cool-climate regions, which include parts of northern Europe, Canada, New Zealand, and northeast USA, are characterized by shorter ripening periods and/or suboptimal mean temperatures (9°15°C, 48°59°F) during the late ripening season. The rate of malic acid respiration is significantly slower in cool climates, resulting in immature grapes at harvesting, containing a high TA content and low pH. In these conditions, malic acid concentrations are almost always greater than those of tartaric acid.

Deacidification Correction Methods

Deacidification is the process of decreasing the TA of must and wine, leading to an increase in pH. There are several options available to bring acidity into balance. Using one tool, or several in combination, can help control high acidity that comes along with the cool climate varietals. Strategies to reduce acidity may be by chemical treatment or biological in nature. Generally, acidity and pH adjustment can occur at almost any stage during vinification. However, deacidification is typically done prior to fermentation for several reasons.

Chemical Treatment

Titratable acidity of the wine can be decreased and pH increased by addition of carbonate salts such as potassium bicarbonate and calcium carbonate. These salts will react with the excess tartaric acid to produce hard soluble tartrate salts, which will precipitate and lower the TA. Before adding these salts, it is necessary to have a baseline reading of both TA and pH and to follow-up with a TA and pH analyses.

Reverse Osmosis

In lower-VA wines (less than 0.7 g/L acetic acid), winemakers can blend with a non-contaminated and lower-VA wine. Ensure that the high-VA wine is sterile filtered before blending. In higher-VA wines (greater than or equal to 0.7 g/L acetic acid), winemakers can use reverse osmosis (RO) to lower the acetic acid concentration (Gardner, 2015).

Biological Deacidification

The yeasts which are involved in the fermentation process affect the final quality and organoleptic characteristics of the wine, including acidity levels and specific organic acids produced.

Malolactic fermentation (MLF) is done by the lactic acid bacteria, which converts malic acid into lactic acid. Upon completing a full malolactic fermentation, the acidity can be reduced, depending on the amount of malic acid consumed (Section 7.2).

Blending

Blending is a common practice that is mainly used to create balance and style of the wine (Section 8.6). It's also used as a method to adjust the acidity of the must or wine.

Amelioration

In certain winemaking regions of the world, it is permissible to add liquid sugar (Section 3.3), water (Section 3.2), or a combination of sugar and water, to reduce the acidity and/or increase the sugar content of the grape must or wine.

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