Ever opened a bottle of wine and seen crystals floating on the bottom or sticking to the underside of the cork? These are harmless tartaric acid crystals. Welcome to the strange world of acidity in wine. These acid components can be complex, but they are fundamental in determining how a wine looks, tastes and is made.
According to Denise M. Gardner, a winemaker from Pennsylvania, our mouths instinctively respond to acidity. Want to see how acidic a wine is? Keep your mouth open after you take a sip. When you start salivating, your mouth reacts to the acid. The more saliva, the more acidic.
The pH scale
Wine contains many acids, but the two main ones that occur naturally in grapes are tartaric acid and malic acid. What we commonly call acidity is technically called total acidity or titratable acidity.
"Titratable acidity is related to how our mouth works," Gardner says. "The more saliva you need to come in contact with a liquid, the more acidic it tastes," she says.
"Titratable acidity is related to pH, but they measure different things. While titratable acidity measures amounts of acid, pH measures the strength of those acids. The pH scale is measured from 0 to 14, with the ends of the spectrum being the strongest. "
"Usually, if a wine has high acidity, it has low pH. High acid / low pH wines are stable because their environment discourages the growth of bacteria and other microbes."
Also important to remember is that the numbers on the scale are unwieldy. "I think pH is more on the chemical side, and titratable acidity is more about the flavor profile of those acids," says Alison Thomson, owner/winemaker of LA Lepiane Wines in Santa Barbara, Calif. "A high acid wine is more lemony, and it makes your 'mouth water.' It makes you want to drink more. I see pH as a reflection of the stability of the wine."
How does acid affect the way a wine looks and tastes?
Acidity is measured on the pH scale, where a lower pH number indicates higher acid levels, while a high pH means lower acidity. By comparison, acidic white vinegar tends to have a pH of 2.5, while milk has a pH of 5 to 6 and water has a pH of 7 (neutral). The pH of a wine ranges from 3 to 4.
Red wines with higher acidity are more likely to have a bright ruby color because the lower pH gives them a red hue. Red wines with higher pH and less acid can take on a blue or purple hue. Wines with lower acidity can also take on a brown color because they are more susceptible to oxidation. It may not be as noticeable in red wines, but can be unpleasant in young white wines.
"Oxidation can become a problem regardless of pH, but the reaction occurs more quickly at higher pH levels ", says Gardner.
A wine with high acidity will usually be harsher and more acidic in flavor. A low-acid wine will feel softer and rounder on the palate. If done carefully, it can be a lovely, luscious feeling, but when low acidity is combined with high pH, a limp or almost soapy feel can result.
A wine with high acidity will usually be harsher and more acidic in flavor.
A low-acid wine will feel softer and rounder on the palate.
Acidity provides part of the backbone needed for long-term aging, so highly acidic wines are more likely to improve over time than wines with smaller amounts. The stability of wines with high acidity/low pH helps with aging. Conversely, wines with high pH are more susceptible to contamination.
Normally, these problems are corrected in winemaking by adding sulfur dioxide, which helps absorb some of the oxidation that would fuel microbial growth. But it takes much more sulfur dioxide to get the same effect in a wine at a pH of 4 as a wine with 10 times more acidity at a pH of 3.
Wines with higher pH need more sulfites to protect them from oxidation, as this reduces the effectiveness of the sulfites. In addition to legal limits on sulfur additions, winemakers must ensure that their wines do not take on unpleasant sulfur-like flavors, such as rotten eggs or cooked cabbage.
It's all about balance
"With higher pH wines, there is a recommended amount of sulfur you can add to make a wine microbiologically stable," Thompson says. "But if you really follow that, your wine will just taste like sulfur. You have to consider a lot of different factors. Looking at acid is one component, but tannin and alcohol are also important components. "
Where wine gets its acidity
The acidity of a wine begins in the vineyard. Potassium found in the soil can find its way into the grapes and increase alkalinity, which helps neutralize acidity and increases pH.
Unripe grapes have a high acidity level, but this decreases as they ripen. Grapes grown in cooler climates tend to contain higher acidity because there is less heat and sunshine available to increase the sugar and pH levels of grapes. A winemaker can increase acidity by adding tartaric acid to the grape juice before fermentation. The process is common in warmer climates, where grapes can become overripe and pH can get too high.
Sometimes a winemaker may face the opposite problem: excessive acidity. If a wine seems too acidic, malolactic fermentation may be encouraged. It converts aggressive malic acid, the kind found in green apples, into softer lactic acid, which you might know best in milk.
"Malolactic fermentation is an example of a winemaker manipulating a wine's acidity problem." - Denise M. Gardner, winemaking consultant
Almost all red wines undergo malolactic fermentation, but it is more of a stylistic choice in white wines. Many people familiar with this process know that it plays a role in creating buttery styles of Chardonnay, but that flavor can be avoided if it is not desired. The key point is to reduce acidity.
"Malolactic fermentation is an example of a winemaker manipulating the acid profile of a wine," Gardner says. "The acid concentration doesn't necessarily change, but you change the identity of the acid from malic acid to lactic acid. So there will probably be a pH change, but there will also be a change in acid levels. You can taste that change ... because lactic acid makes a wine softer and less acidic."
Remember those tartaric acid crystals? If a wine contains a lot of tartaric acid at bottling, the acid can clump together into crystals as it cools. The crystals, also known as tartrates or wine diamonds, dissolve back into the wine when heated.
By Noelle Hale / @WineEnthusiast / Photos by Getty
