Lively. Racy. Silvery. Bright. However you describe it, acidity is what makes a wine sing. This month, we’re going to talk about the role acidity plays in balancing a wine, and how it affects other aspects as well. We’ll also take a look at the key factors that influence acidity. Buckle up and take a ride on the A(cid) train with us.
Acid is essential to good wine. The various acidic compounds found in the bottle contribute a fresh, crisp counterpoint to the other elements like sweetness and tannins, as well as helping to preserve the wine. Acidity is a complex subject, so we’ll start with the basics.
On the molecular level, an acid is a solution containing free protons. These protons are the nuclei of hydrogen atoms whose electrons are in use in a molecular bond. The number of free protons in a solution determines how acidic it is. Acidity can be measured in two ways: pH or titratable acidity in grams per liter. The former measures the actual number of free protons in a solution, while the latter compares the mass of all acidic compounds to the mass of the solution. Confused yet?
Think of it like this: pH is a quality measure, total acidity is a quantity measure. Because different acids release different numbers of protons in solution, some acids are stronger than others. This can lead to the immensely confusing situation of two wines with the same total acidity by mass having two different pH measures. A good example of this can be seen in wines that undergo malolactic fermentation, in which malic acid is converted into the weaker lactic acid. The total acidity has not changed, but there are fewer free protons, which makes the wine less acidic overall, and contributes to a softer mouthfeel. One other fun fact to keep in mind: pH is expressed as a negative logarithmic value, so higher pH translates to lower acidity, and a small change has a relatively large effect.
When we talk about a wine’s balance, acidity is a key factor. The sour, fresh “bite” of tartaric acid, the main type found in wine, cuts through sweetness and mellows the astringency of tannins, and is responsible for the “backbone” or “focus” we love in good wine. Acid is especially important to dessert wines to counter the sweetness.
Acidity also helps to preserve a wine, and can extend its aging potential. White wines with high acidity tend to age better than their low-acid counterparts due to the acid’s preservative effect. Additionally, acid tends to interact with alcohol to produce esters, highly aromatic compounds which add a great deal of complexity to a wine. Most esters are produced during fermentation, and tend to break down in the bottle. A wine with good acidity, however, can undergo esterification during aging, revealing hidden aromas. This transformation can be significant enough to change the character of a vintage. For example, the 2010 vintage in Austria was remarkably difficult, with cool, wet conditions throughout the growing season. The grapes struggled to attain ripeness, acid levels were high, and the vintage was largely panned by wine critics. After nine years in the bottle, however, the wines have developed lovely aromatic esters, and are finally enjoying their day in the sun.
Acidity plays a major role in pairing wine with food as well. High-acid wines are a versatile pairing tool, as they can both complement acidic dishes and cut through heavy ones. Think Grüner with asparagus, or Riesling with schnitzel. While some other wines pair well with specific dishes, we always look to our acid-rich standbys when faced with difficult pairings.
Acidity is dependent on many factors, and a vigneron must account for many variables to ensure proper balance. Variety, growing region, vintage-specific weather events, and even the time of day the grapes are picked will greatly influence the acidity and overall balance of the finished wine. It’s a delicate endeavor, but it pays off.
Of all the factors contributing to a wine’s acidity, growing region is perhaps the most influential. Grapes grown in cooler regions take longer to ripen, and retain their natural acidity more than grapes from warmer regions. Cool-region white grapes such as Grüner Veltliner, Riesling, and Furmint thrive in these regions.
Grape variety plays an important role as well. Some grapes, most notably Riesling, have a natural tendency to retain acidity during ripening. Others, such as Grüner Veltliner, struggle to maintain acidity, especially during warmer vintages. Furmint, normally used as a blending grape, has natually high acidity. These varietal differences demand thoughtful winemaking decisions. While potential acidity is determined by growing region and variety, the acid in the finished wine is always up to the winemaker.
The instincts and experience of the winemaker ultimately determine when the grapes are picked. If they are picked too early, the grapes may not be physiologically ripe; picked too late, and the acidity is lost. Some winemakers even plan harvests in the cool early morning hours to ensure optimal acid levels.
The challenge of preserving and balancing acidity in a finished wine is a chief concern of vintners, and they all have their own ways of tackling it. In the Wachau, Peter Veyder-Malberg is known to pick his grapes earlier than other producers in the area. His strategy is primarily intended to avoid overripening and fungal infections, but it has the added benefit of preserving acidity. In Burgenland, Günter & Regina Triebaumer painstakingly match grape varieties to soils for optimal development. In Alsace, Domaine Bernhard & Reibel employ similar site selection to ensure that their Rieslings express the lively acidity they are known for.
Variety: 100% Grüner Veltliner
Vineyard: Terraced Loibenberg site, Gneiss and Löss
Analysis: Alcohol: 12.5%; Acid: 4.7 g/L; Sugar: 1.0 g/L
Variety: 100% Riesling
Vineyard: Single vineyard “Rittersberg,” Mica-rich Dambach Granite
Analysis: Alcohol: 14.0%; Acid: 3.82 g/L; Sugar: 2.2 g/L
Variety: 100% Furmint
Vineyard: Weathered slate soils near Rust
Analysis: Alcohol: 12.0%; Acid: 7.0 g/L, Dry
The Silver Thread
Acidity is the silvery thread that wines from cool growing regions share. The tart, bracing zing of a balanced, well-made Riesling, Grüner, or Furmint is surely one of the most rewarding pleasures of wine enjoyment. Making an expressive, balanced wine is no easy task, and acidity plays a key role. From growing region to picking time, the winemaker must keep a close eye on all the factors that influence acidity, but the reward is worth the effort, and these wines really do sing!