Q&A with Paul: “Do winemakers need to add tartaric acid to keep it fresh and age-worthy?”


Thanks for the question Andrew!
We explore why we add acid to wine, looking at the chemistry, and, impact on taste, as well as how it will affect the wines ability to age.

First question, why do we add acid?

To achieve balance in a wine where tannin, alcohol, and, flavour are in harmony.

The amount of acid can be too high making the wine sour or too low giving it a flat, lifeless mouthfeel.

Wines with higher acid level and lower pH tend to make fruit appear fresher and colour brighter. For the wine geek, you can check out the chemistry behind this in the video in the article “Just How Does Sulphur Affect Wine? + A Pro Tip for Buying Old Wine”.

The amount of acid in the wine is related to the pH, however, many chemicals in the wine impact (buffer) how direct that relationship is.

The pH impacts microbial stability, a low pH creates a less friendly environment for bad bugs to grow. It also makes any Sulphur added more effective and able to kill bugs.

Technically, many winemakers target a pH of less than 3.65 in a finished red wine. At the end of the day technical science of winemaking acid, this ends up as a wine style decision.

That covers balance and microbial stability.

What about the ability to age and stay fresh?

Well, the lower the pH and the higher the acid the fresher the wine will stay.

To answer your Barossa question acid will be added to many wines.

The article referred to above explores this in detail with a white wine experiment I conducted over 20 years with wine bottled at 2 different Sulphur levels.

Typically warmer climates need to add more acid than cooler climates, some cooler climates need acid removed!

Within a region, different vineyards as a result of their management, vine age, wine balance, yield, will give different pH and acid profiles.

Older vines with lower yields and better balance generally have better pH and acid profiles.

Timing of picking influences acid levels dramatically. As fruit matures acid reduces. The riper the fruit the lower the acidity and higher the pH. The shift to picking earlier across many of Australia’s wine regions has seen greater retention of natural acidity from the grapes and reduced the need to add acid.

If a vineyard has been loaded with potassium this can dramatically reduce acid levels in a wine as the potassium will encourage the formation of crystals with tartaric acid that will then fall out of solution.

As a winemaker, you then have to decide what type and more importantly when to add acid. In Australia, there are a number of different acids that can be legally added to wine.

For reds it’s normal to add tartaric acid.

For whites it’s common to use tartaric acid, and, less so to use citric acid, lactic acid and malic acid.

The trick is to know the style of wine you want to make and get everything under control early. There is a fair range of pH and acid levels that will be technically correct giving you room to move.

Wine is a chemical soup that changes dramatically during fermentation, the longer you wait the harder it is to get it under control as the multiple chemical equilibriums start to move against you.

So in general, if needed, I’d hit it hard and early. The earlier you sort it, the better the integration of the acid, and, end texture of the wine. If you add a large amount of acid late in the winemaking process, that acid will not integrate as well, and, will give the acid a hard texture in your mouth.

There is an equilibrium that exists between all the different forms of tartaric acid, yes there are several, in grape juice and wine. If you keep the pH of the juice or must below 3.56 the pH will drop if precipitation of tartrate, the crystal combination of K+ (potassium) and HT- (one of the forms of tartaric) known as Wine Diamonds occurs. If the pH of the juice is above 3.56 and tartrate forms then the pH increases. The presence of alcohol increases the pH at which this little bit of wine chemistry magic happens to 3.65.

Hope that helps! Short, but, very complicated question!

Making wine with real personality and intrigue, wine that says DRINK ME, is not easy. Understanding the ‘rules’, and, having the numbers from the lab, allows you to break them, and, push the boundaries, with the confidence that you’re less likely to bugger it up. The greatest sin a wine can make is to be boring!

There are too many acids in wine to cover them all here. Some are present in the grapes and juice, others are produced by yeast or bacteria, some are converted from one acid to another by bugs.

Finally, there are heaps that can be legally added, all of them have different perceived intensity and impacts on aroma and flavour as well as well as strength ie the ability to change the pH of the wine.

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