Acid is a fundamental component of wine and impacts wine structure and microbial stability as well as sensory perception. If a wine has too much acid it can taste sour but if it has too little it can taste dull, lifeless and flabby. In an ideal world, all harvested grapes will contain an exact balance of components and the desired acid level for the winemaker’s intended wine style. Unfortunately, this is near impossible as climactic variations and weather events, varietal differences, and varied wine styles all impact acid development and stability.
Depending on the style of wine created, vintage, region and varietal, a winemaker may focus on increasing, decreasing, or maintaining acidity from harvest to secondary fermentation. Malic and tartaric are the two primary acids found in wine. Malic acid is highly subject to consumption by grapes and typically provides a “green apple” sort of freshness to wines. In warm regions and vintages, malic acid is typically low as it can be utilized by the grape as fuel to process the “dark cycle” during respiration. For example, the climate of the Barossa Valley in Australia enables grapes to accumulate sugar easily, albeit at the expensive of malic acid loss. Furthermore, popular and intensely ripe and fruit-dominated winemaking styles such as Australian Shiraz and Napa Valley, California Cabernet Sauvignon, may cause winemakers to pick grapes at the latter stage of ripening wherein malic acid levels are low.
In contrast, since grapes don’t utilize tartaric acid as fuel , these levels remain relatively constant throughout berry development and ripening. Typical acidity levels are between 4.5 and 8.5 g/L with corresponding pH levels of 3.1 to 3.8. Red wines are more likely to have higher acid changes post fermentation due to the shift that potassium can cause via binding with tartaric acid. As a result, low acid varieties, such as Syrah grown in warm climates, may have pH’s well above the dangerous 4.0 mark. High pH wines are noted to have less crisp flavor, exhibit flatness, have decreased microbial and oxidative stability and in red wines, decreased color intensity. Now that’s wine for thought!