Acidity is one of the most important components in wine, as it affects a wine’s flavor, balance, texture, color, smell, and it is important in protecting it from undesirable bacteria. It is also one of the main characteristics that people respond to quite strongly, both positively and negatively. Those who say that they don’t like sour or tart wines usually want a wine with lower acidity. Those who like more acidity complain that low acid wines taste fat or flabby. One of the main measures of a wine’s acidity is its pH. This is a 14 point scale that measures a solution’s alkalinity or acidity. Water is neutral and has a pH of 7. Everything below 7 is acidic, and the lower the pH, the higher the acidity. Most white wines have a pH between 3.0 and 3.3, and red wines between 3.3 and 3.6. Remember that the lower the pH, the more acidic – and it is more acidic by a factor of 10. A pH of 3 is 10X more acidic than a pH of 4.
There is a second way acidity in wine is measured, and it is grams/liter – which gives you the percent of acidity found in a wine. It is related to pH. A California Chardonnay which has 5.8 grams acidity per liter (which is the same as 0.58%), would have a pH around 3.4. A Late Harvest Riesling may have 11.0 g/l (or 1.10%) acidity and a pH of 2.9. Interestingly, a lot of acid is required to balance out all of the sugar.
Grapes contain acids naturally, and thus the wines made from them contain acids as well. Grapes grown in cool climates (Europe) have higher acidity than grapes grown in warmer climates (California). This is just the opposite of sugar production: the warmer the climate, the higher the sugar. Three primary acids are found in wine grapes: tartaric, malic, and citric acids.
Tartaric acid is rare in other plants but abundant in grapes. During flowering, high levels of tartaric acid are concentrated in the grape flowers and then the young berries. While some tartaric acid is free standing in wine, the majority of it concentrates in potassium acid salt (tartrates). These tartrates can bind with other substances in the wine during fermentation (or after) and crystallize into tiny pieces that look like shattered glass. This sediment is harmless, and it is not a flaw. It forms on the bottom of the cork and sometimes falls to the bottom of the bottle. Since it is sometimes off-putting to the wine buyer, especially if it is an expensive wine, winemakers will sometimes intervene to force the crystallization through cold stabilization of the wine and then filtering these “wine diamonds” out. But, again, it is not a flaw, and it does not affect the taste of the wine. Just letting the bottle sit upright for an hour or so before drinking will let all of the tartrates fall to the bottom. Finally, if a winemaker needs to decrease the pH of the wine, extra tartaric acid can be added for balance.
Malic acid is found in nearly every fruit and berry, and its taste is very similar to green apples. It is often so strong that it needs to be softened through a process called malolactic fermentation (MLF). Almost all red wines naturally undergo MLF, and some white wines are prodded into a secondary malolactic fermentation through inoculating them with a bacteria. In the process malic acid (apples) is turned into lactic acid (milk), which is much softer and creamier. I used to be confused when a winemaker would tell me that a given white wine had seen 50% MLF. What this means is that one barrel of it had no MLF and the other did, and they were blended together.
Citric acid is plentiful in lemons and limes, but not so much in grapes. Most of it is consumed by bacteria during fermentation, leaving 5% or less of it than the tartaric acid in the wine. But it can impart a nuance of citrus to some wines.
This blog has been pretty technical so far. Now I want to take a more general view of acidity in wine. For me, wine isn’t real wine unless it has good acidity. It is the acidity that perks up the taste buds and makes food taste better. And I guess that since I am of Italian decent, wine for me is an experience only half lived if it does not accompany a great meal. I also find that low acid wines can slip down too fast, which can result in headaches the next day. With higher acid wines, their tartness makes me sip them more slowly. So many customers ask me why in America wine gives them headaches, while in Europe it doesn’t. For most the reason is simply alcohol: the European wines are lower in alcohol and the acidity makes you drink them more slowly.
But you don’t have to have the same tastes as I. There are great wines with lower acidity, and I sell many. But to find the right wine for the right person, the merchant needs to know more about the customer’s taste for acidity than just about any other preference. To sum up, acidity and tartness/sourness go hand in hand. But many customers use the adjective “bitter”, when they often mean sour. Wine can be slightly bitter at times, but this usually comes from the tannins in the wine. And this will be the segue into the topic for my next blog.