Acid in Wine: A Tutorial

Let’s pretend this is Burgundy. It’s the peak of what would be the best week of your Chardonnay harvest. It’s been over one hundred days since the fruit set on the vines. In an ordinary year the grapes would be perfect, but it’s raining. It has been raining for weeks and you are beginning to taste water in the berries as you walk through the vineyard. If you try to wait out the rain, the grapes may be so dilute that making a memorable wine from the saturated grapes would be difficult.

Or, you’re in the Rioja Alta. The sweltering heat has begun to ripen the Tempranillo grapes faster than expected. You fear that the potential alcohol will be so high by the time the grapes get to the winery that the remaining acidity will be imperceptible. Even the skins on the grapes are beginning to shrivel.

In both cases, due to two very different causes, the grapes arrive at the winery in an imperfect state. On one hand, the pH has been increased by the absorption of rainwater. On the other, the pH is high because of over-ripening. In both cases, some acidification is necessary to achieve balance in the final product.

A quick note on pH in wines before we begin adjusting the must. In wine, we typically see a pH of between 3 – 4. For each wine there are multiple styles that can be made, but as a standard whites have a higher acidity and thus a lower pH – closer to 3.0. Red wines have a higher pH and thus a lower acidity – closer to 4.0 (although typically closer to 3.5). The closer a wine’s pH is to 4, the less stable the wine will be in the long run. The closer a wine’s pH is to 3, the more stable it can be, but this is not a certificate to add acid to protect he wine from microbial problems. What we are attempting to achieve is balance.

So, your dilute white Burgundy grapes have a must weight of 22° brix (or 12.2° Baumé), which could be quite normal, but your pH is around 3.5. As you go through fermentation, surely the pH will increase and the final wine will seem flabby, fat. You require something more from these grapes. Your pH should be somewhere around 3.2. Adding a little acid can make this so.

In Rioja, your red wine must weight is much higher, somewhere around 30° brix (16.6 Baumé), and the pH is 4.1. The amount of sugar in the must will certainly result in a higher degree of alcohol and protect it from potential problems, but the pH needs to be lower for the wine to taste right – varietally speaking.

You can add acid in a number of ways. Lemon juice has been known to adjust the pH of white wines made at home, but this is a mediocre increase in acid and significant aromatic addition which may or may not be something you ultimately desire.

A neutral aromatic acid powder will typically do best in any situation (red or white): Tartaric, Citric and Malic acids are used in industrial settings and are therefore the best. They come in small and large amounts. The best of the best is Tartaric acid.