What Does Acidity Do To Wine?
Acidity: many who have attended a wine tasting or read tasting notes have heard this term thrown around. Good acidity, bad acidity, acidity on the finish, on the mid-palate. It has balanced acidity, too much or too little. But what is it really?
“It’s the level of tartness in a wine,” explains Master of Wine Amy Christine, a wholesale representative for Southern California’s branch of Kermit Lynch, and co-owner of Black Sheep Finds in Lompoc, California. “The more your mouth is watering, the higher the acid.”
This tasting term applies to the sensation a wine leaves in your mouth. The source of this sensation — its intensity, flavour and type — are naturally occurring wine acids that play a large role in winemaking.
“There are three main acids [in grapes],” says Dave Carson, winemaker at See Ya Later Ranch in Okanagan Falls, British Columbia. “Tartaric acid, malic acid and citric acid. But citric acid is in a really small amount … it’s more about the tartaric and the malic and how they interact together.”
“Tartaric acid is unique to wine,” mentions Paul Pender, winemaker for Okanagan Falls’s Tawse Winery. “I think there is only one other fruit that has it.”
Each acid plays a different role in the winemaking game. Tartaric acid is a background player, supporting and stabilizing the wine as it evolves. “Tartaric preserves the stability of the wine,” says Pender. “If the pH is under three-point-five, the sulphur you add is a preservative; over, it is no longer effective.”
“On its own, tartaric acid doesn’t affect the colour. But it affects the pH — if it’s a high pH, the red wine tends to be less stable, less red and more brown,” says Carson. “High pH can also usually affect age-ability. Wine with low acid and high pH can be described as flat and flabby.”
The pH levels don’t discriminate; they can be changed by malic acid as well. “Malic acid is not stable,” says Christine. “Following alcoholic fermentation, malic acid will naturally convert to lactic acid, softening and lowering the acidity and raising the pH.”
The instability of malic acid causes instability in the wine that can either be neutralized through malolactic fermentation or controlled to create a specific flavour profile. “Malic is a harsher acid, often described as a green apple acid,” says Carson. “For instance, if you have a very cold year and a high malic acid concentration, you might have a wine that comes off very hard in the finish.”
Even though malic acid is more prominent on the palate, it has less influence on the structure. “Tartaric is a strong acid and malic is a weak one,” says Pender. “The other [important] acid is lactic acid.”
If the winemaker doesn’t want to have the harsh, green apple flavour in their wine, they will use malolactic fermentation to convert malic acid into lactic acid.
“It’s actually a bacterial conversion of malic to lactic acid,” corrects Carson. “People call it fermentation, but that’s incorrect.” This conversion softens the acidity of a wine, taking advantage of the smooth lactic acid to create a different flavour profile in the final wine.
Lactic acid does not naturally occur in wine grapes. It is a by-product of the fermentation process and is used at the winemaker’s discretion, much like all of the other acids.
“Malic and tartaric are the primary acids present in grapes,” says Christine. “Tartaric and lactic are the primary acids found in a finish wine, assuming it has gone through malolactic fermentation.”
“Lactic acid is a lot softer of an acid,” mentions Carson. “As the conversion continues, the total acidity of the wine goes down. It becomes softer and tends to have more of a mouthfeel.” This is why red wines go through malolactic fermentation — because red wines should be soft and round, rather than sharp and tart.
The winemaker can control the lactic acid levels by choosing whether or not to use malolactic fermentation, but controlling the levels of tartaric and malic acid in the wine is a bit more complicated. Both are naturally occurring, which means that winemakers have to pay careful attention to the vines, climate and temperature.
“The level of acidity in a wine is related to climate,” says Christine. “Different regions and climates naturally produce different styles of wine, some of which are stylistically more acidic than others.” In fact, temperature and climate determine the rate at which the acid levels in the grape change.
“Tartaric acid is predominant [in the grape],” Carson explains. “It’s at a fixed level. As the grape ripens, the berry gets larger in volume. Tartaric acid goes down … because of dilution — more things come in.” At a fixed level, it means that when the grape berries are small, they are highly acidic because there is no juice or liquid to mix with the tartaric acid. But as they ripen — grow in size and increase in juiciness — the tartaric acid is diluted, combined with the natural sugars, other acids and the juice of the berry.
Malic acid is also prey to dilution, but what makes it less prominent than tartaric is that it escapes the berries through respiration — evaporation through the skin of the berries. “This is mostly related to weather,” says Carson. “Mostly the nights. If you have very warm nights, you’ll get lower malic levels because when it’s warm, the respiration levels increase. If you have very cold nights, higher levels of malic.”
The respiration and ripening of the grape changes the ratio of the acids within the berries themselves. “Malic acid is high prior to véraison, but as grapes ripen, malic acid will respire and tartaric, the more stable acid, will become predominant,” says Christine. “Cooler climates, like those in Mosel, Germany, produce grapes with higher levels of malic acid due to the cooler temperatures and low rates of respiration.”
“Malic acids can be virtually nothing if you have a really, really hot year,” states Carson. “It gets used up in the respiration.”
The two things winemakers need to watch (among the million other things they are taking into account) are ripening speed and temperature levels. This can be tricky, even for very experienced winemakers. Winemakers monitor the vineyards to determine when to harvest, which is one of the only ways to control the acid levels.
“What you do in the vineyard is one of the most important things you can do in winemaking,” says Pender. “If I have a hotter year, I’m going to pick earlier. In 2012, we picked our Chardonnays in August, because it was so hot. In 2014 it was cool, so we picked the first week of October.”
“This year for our wines at Black Sheep Finds, we based most of our picking decisions on the pH of the grapes,” says Christine, giving her unique experience from a warm climate winery. “We want to retain natural acidity, so we are in general picking earlier in order to achieve better fruit to acid balance.”
Unfortunately, sometimes the harvest date isn’t enough. During crushing or fermentation, the winemaker notices that there is too much or too little acidity. The previously mentioned malolactic fermentation is one way to reduce the acidity but there are a few other techniques winemakers can use to fix a wine’s acidity.
“Blending, watering back (where legal), cold stabilization (where tartaric acid precipitates out of the wine), malolactic fermentation, addition of calcium carbonate, ion exchange,” Christine lists.
If the wine has too much acidity, but they don’t want to remove the malic acid, they balance with sugar. “You can balance acids off with residual sugar,” says Carson. “You can add sugar back by sweet reserves or by stop-fermenting wines, where you remove the yeast or inhibit its ability to convert sugars.”
There are risks to adding sugar though. “If you have high acidity and try to balance with too much sugar, you can get ‘sweet and sour’,” warns Carson. “Where you have a wine that comes off as sweet, then there’s a hole in the middle and then it’s sour.”
There are fewer options for winemakers if acidity is low. “Blending and acid additions prior to fermentation,” states Christine. Blending works if you have a batch that is high in acidity and a batch that is low. But when there is no batch available to balance the wine, that’s where acid additions come into play.
“Typically, 99 per cent of the time when winemakers add acid, they add tartaric,” Pender states. “When aging wine in a barrel, the tartaric acid precipitates out and forms a crystal. Winemakers buy bags of tartaric acid … the trick is to add enough to balance the pH and not make it taste like you’ve added acid.”
“People add tartaric acid right at the crushing, to adjust the pH so the wine is microbially safe,” adds Carson. “The sooner you make any additions to wine, the better the wine can mellow.”
Acid additions don’t happen very often, with winemakers working hard to ensure it isn’t needed. “We are winemakers and want to make it as natural as possible,” says Pender. “But in the end, we want to make a wine that is safe during its lifespan.”
Knowing how acidity comes into play and which acids are present isn’t enough to truly understand “acidity.” What matters to the consumer — i.e. you and me — is how the acidity appears in the final product.
“Acid plays a couple different roles — a sensory role, the taste, the sharpness of the palate,” explains Carson. “It also plays a role in the juice and wine from a micro stability perspective. The lower the pH, the less the microbes want to live in it.”
Wine acids provide the final product not only with the tartness but also colour, structure and the ability to age without deteriorating. “We can use the existing acids in the wine to influence the flavours,” says Pender. “The acid in the wine gives it its longevity and freshness.”
“Malic acid has the green apple. Sharp,” says Carson. “Tartaric is a less harsh apple than malic … but not as mellow as lactic acid; it does provide flavour characteristics.”
Sensing the acidity in a wine is about using more than just your taste buds. “If it’s a red wine, you can look at the colour and taste it,” says Pender. “Trust your palate. Taste if it’s bright and crisp and has that nice sharpness you get with acidity. Or is it softer, flabbier and more on the sweet side.”
“You pick it up at the middle to the end, mid-taste would be the best way to say it,” says Carson. “It’s a sharpness. You will taste it throughout, but in a white wine it’s more on the end and a red, it’s more in the middle. It’s a lot where the wine actually hits your tongue.”
There are some wines that lend themselves to the crisp, sharp, freshness that comes from higher acid levels.
“I like high acid in my Rieslings, then I balance them with sugar,” says Pender. “I often don’t allow malolactic fermentation in Chardonnay because I like a lot of acidity … I want them to be crisp and fresh, with the green apple taste.”
“The secret to great balance in Champagne is adjusting the sugar to match the wine’s acidity,” Christine chimes in. “Riesling has residual sugar and the high acidity helps balance the residual sugar, making the wine appear perceptibly less sweet.”
However, the final result shouldn’t scream “acidic” — it should be balanced and enjoyable.
“At See Ya Later Ranch, all of the reds go through malolactic fermentation,” says Carson. “For the whites, I don’t really talk about the acids and sugars separately. I don’t really focus on acidity in wine … it’s about finding that balance.”
Next time you open a bottle of wine, try to find that sensation on the tongue, mid-palate or finish. Maybe it’ll be tart, crisp and fresh. Maybe it’ll taste like green apple. Perhaps you’ll get a bit of butter or a hint of smooth cream. Whatever you sense, now you’ll know the term to describe it … and perhaps impress a few friends by identifying which acid was used.
Acidity in Grape Varieties
Master of Wine Amy Christine gives us a rough guide on the acidity levels in wine. “I’m more the type to say drink what you want and eat what you want,” says Christine. “That said, high acid wines pair great with creamy foods. Acid cuts through fat and can balance the richness of a dish.” Experiment by comparing the cold climate version with its warm climate counterpart to see if you can tell how the acidity changes by region.
Riesling, Sauvignon Blanc, Pinot Noir, Nebbiolo
moderate to high acid
Chardonnay, Sangiovese, Merlot, Cabernet
Viognier, Roussanne, Tempranillo (though this varies a lot)