How does the acidity of wine vary with temperature?

Dear Dr. Vinny,

I want to do a wine science experiment, and I’m wondering about factors that could influence pH. How does a wine’s temperature affect its acidity?

—Nayun, Australia

Dear Nayun,

Thanks for your great follow-up to last week’s question about bottle aging and acidity.

As I explained in that answer, once a wine has gone through fermentation and is sealed in the bottle, the chemical composition doesn’t change very much. (That’s assuming you’re not boiling it before your science experiment!)

As in all chemical reactions, temperature absolutely plays a role in the changes that do occur in a bottled wine over time. Generally speaking, reactions happen faster at higher temperatures, since there’s more energy available and the molecules are moving around faster. That’s why wine storage should be cool and consistent, which slows down these processes and ensures they happen at a desirable, steady, slow pace.

Now, you might want to put on your lab goggles, because I’m going to get a little technical. (And don’t forget to take appropriate safety measures during your experiment!)

The pH of any solution, including wine, will vary with temperature. Even the pH of pure water will decrease as temperature increases! Higher temperature means more free hydrogen ions—which in turn means a lower pH.

However, this change in pH doesn’t necessarily indicate a change in acidity, which is a measure of the ratio of hydrogen ions to hydroxide ions. Since there will also be more hydroxide ions at higher temperatures, the actual acidity of a solution will stay the same, assuming the increase in temperature doesn’t induce reactions that change its fundamental chemical makeup.

The bottom line is that unless you’re getting your wine really hot for your experiment, you’re unlikely to see any significant change in acidity, though the pH will change very slightly. As such, you may need to adjust your calculations to account for temperature differences.

Alright, goggles off! The far more important point for most wine lovers has to do with serving temperature and the way we perceive a wine’s acidity on the palate. If a wine is served ice cold, the acidity will probably seem sharp. If a wine is served too warm, the alcohol will stick out more in relation to the acidity, and the wine will seem flabby.

That’s why serving wine at the right temperature—where the acidity should present itself in balance, just as the winemaker intended—is crucial for helping your bottles show their best.

—Dr. Vinny