Dr. David Muhleman

The-Wine-Educator    WINE & SPIRITS EDUCATION AND CONSULTING SERVICES FOR THE CONSUMER AND THE PROFESSIONAL

Acids in Wine

Wine is inherently an acidic drink. Even wines that taste sweet to the consumer are very high in acid; the residual sugar simply masks the acidic character. One of the keys to a sweet German Riesling is the “racing acidity” underlying the sweetness.

Acid is also one of the two primary indicators of when to pick the grapes. Young grapes have high, high, acid and very low sugar. Most winemakers want to pick their grapes at the point where sugars and acids are at their maximum. Past that point, sugars continue to rise as acids start to drop. Without the acids, the wines become “flabby” and lose much of what makes the liquid “wine.”

Acids are also one of the three principal ways of preserving wine for aging. High alcohol, high sugar, and high acid are the three elements that help a wine mature with acid. Again, a German Riesling with high residual sugar and high acid, can easily age for 20 years.

Acid in wine (along with alcohol) is one of the reasons bacteria rarely grows in wine. With the exception of a few harmless (to your health) bacteria, nothing harmful can live in wine. That may be why in olden days wine was healthier to drink than the local water supply. So acids (as well as sugars) are the keys to wine chemistry.

There are three principal acids which come from the unfermented grape: Tartaric, Malic, and Citric. During the fermentation process three additional acids may be formed; Lactic, Succinic, and Acetic.

The first three (of which tartaric is present in greatest amount) are a function of the grape growing, and grape harvesting. Again, some wines, such as German Rieslings are harvested with high acidity, which is often counterbalanced with residual sugars. Other wines, such as California Zinfandels are often harvested with lower acids and higher sugar levels (producing high alcohol and low acids).

The acid balance of the final wine can be traced back to many winemaker decisions, the most important being the varietal of grape; in that many grapes are fully mature (ripe) and ready to harvest with high acidity still in the grape (e.g., cold climate Pinot Grigio), and other grapes may have lost most of their acids by the time the grape is mature/ripe enough to harvest (e.g., warm climate Semillon).

So the first two places a winemaker has to influence the desired acid balance in the finished wine; are in the vineyard (grape selection, and the harvest decision). The next place the winemaker can influence the desired acid balance in the final wine is in the winery; the fermentation process.

One obvious decision is if the winemaker’s choses to acidify (or de-acidify) the must.  Depending on the Total Acidity, the Titratable Acidity, and the acidity levels the winemaker desires; many regions allow the winemaker to adjust the must’s acidity. This practice has a wide range of possibilities from the addition of additional acid (normally tartaric), to the dilution of the must with additional water, to the addition of additional must of a different acidity, or the addition of de-acidifying base chemicals.

Once satisfied with the acid balance of the must, the winemaker can also manipulate the post-fermentation acid levels through processes such as, malolactic fermentation, cold/heat stabilization, temperature of the fermentation process, oxygen levels (oxidation), and even the process of draining off the free run can change the acidic balance of the remaining wine/must.

Once the alcoholic and the malolactic (acidic) fermentations are complete, the winemaker can still adjust the acid balance (before bottling) through racking, cold stabilization, different aging regiments, barrel/stainless steel selection, temperature control, and blending. Even the acidity of the water used in the winery can be adjusted to affect the resulting wine. And even after bottling, the winemaker can manage acidic balance through bottle aging, and determining when to release the wine.

Generally, allowing the wines to age allows some of the acids to break down and lower the total acidity of the wine. So the winegrower, and winemaker have the ability to control (adjust) the acidity of the wine though their vineyard decisions, through the vinification decisions, all the way to the decision of when to bottle and when to release the wine.

Wine is an acidic beverage. The management of these acids is one of the most important roles of the winemaker, and they have many places in the wine making process to make the decisions to modify the acids in grape juice and wine. Hopefully they make good decisions.