The topic of acids in wines has been the center of discussion many times in our wine circles. It is important to realize that both good and bad acids exist in the wines that we drink. Let's explore the different acids in wines and their influences on the wines that we drink.
Two common acids in wine are tartaric and malic acids, which vary depending on grape variety and region that they are grown. A good example is looking at the Chardonnay varietal from France verses California. A Chardonnay from Burgundy, France has a lower concentration of malic acid than one from Napa Valley California. Both tartaric and malic acids are nonvolatile, meaning that they do not evaporate or boil off when wine is heated. An example of a Volatile acid in wine is acetic acid which is vinegar. Acetic acid boils off easily when heated, and is a bad or undesirable acid in wine. Volatile acidity is part of the fermentation process and is normal when it is about 0.03-0.06% of the final product. One thing to note is that some old Italian wines have acetic acid that can be detected in the aroma and taste and is acceptable by drinkers of this style. This means that it is a little higher than normal, but if it gets too high it also would not be palatable.
Tartaric and malic acid production occur during grape development and is affected by temperature. Warm climates cause the acids to be removed from the grapes through respiration. This causes the wine from a warmer climate to have lower acid than wines from a cooler environment. Chablis from France have a much higher acidity level than a Chablis from California or Australia which is significantly warmer. One key item to remember is that cooler regions produce less sugar (lower alcohol) and higher acidity. Warmer climates produce higher sugar levels (higher alcohol) and lower acid levels. French wines like the Chablis are blessed with high acidity providing a brilliant and vibrant wine, but can be plagued during seasons where the grapes do not get enough warmth and sunlight to produce sugar levels needed for alcohol production.
In France there are requirements on the minimum allowable alcohol level for their wines. To remedy the problem with seasons producing low sugar contents in the grapes, the French Government allows controlled amounts of sugar to be added to the grape must in a process known as chaptalization. Chaptalization is not allowed in California, but is allowed in Oregon and New York, where cold weather can affect grape sugar levels. Warmer climates like California, where sugar levels and alcohol production is not an issue tend to lack acidity. These areas are permitted to add tartaric acid and other acids to increase the acidity of the wine.
Malolactic fermentation (MLF) is a wine making process converting malic acid, which has a tart taste to lactic acid which is much softer on the palate. Some white wines undergo MLF and almost all red wines undergo MLF naturally. Some wines such as Chablis require MLF to lower their naturally high acidity. Since some wines have less malic acid than others, the MLF is not as important in these wines as those with higher malic acid levels. For example, a White Burgundy typically contains less malic acid than a Napa Valley Chardonnay. Therefore, when a white burgundy undergoes MLF, very little acidity is lost and the characteristics of the wine is maintained. But a California Chardonnay contains more malic acid so when it changes into lactic acid the acidity changes appreciably. The problem in cool climates is too much acid, whereas the problem in warm climates is too little acid. For consistency the U.S. measures total acidity (TA) of a wine as all the acid is tartaric. This maintains consistency in the measuring of total acidity in a wine. A high TA is 1.0% which would be very tart to most people. A low TA of 0.4% would result in a wine that is flat tasting without any type of vibrancy to it. Low TA wines are also more susceptible to infections and spoiling. As a benchmark, most red table wines have about 0.6% TA and white wines are usually a little higher.
PH is a logarithmic scale used to measure a solution's acidity level. To put this into perspective, a wine with a pH of 3 is 10 times more acidic than a wine with a pH of 4. The thing to remember about pH is that the higher the pH, the lower the acidity, and the lower the pH, the higher the acidity. TA and pH are related, but are different in the measurement of acidity in wine. The pH represents the active acidity of the wine. If too high, say 4.0 or above, the wine becomes susceptible to spoilage. Low pH inhibits spoilage and will preserve the wine. Tartaric acid is sometimes added to fermenting grape juice in California to achieve an acceptable final pH since some acid is lost during the fermentation process.
Having a higher PH reduces the TA of the wine. For example, a California Chardonnay has a total acidity of 0.58 grams per 100 ml (0.58%) and a pH of 3.4 compared to a TA of 1.10 grams per 100 ml (1.10%) and a pH of 2.91 in a late harvest Johannesburg Riesling with 21% residual sugar. Higher acidity is required in sweeter wines to balance the high sugar content.