How to Measure Acidity in Wine

The Role of Acids in Wine | Recommended Acidity Levels
Measuring Acid Using Titration | Measuring Acid Using a pH meter
Adjusting Acid Levels in Wine |

The Role of Acids in Wine
Before we jump into our discussion of how to measure acidity in wine, it's paramount to first understand why acid levels are important to the winemaker.

Acidity provides the crisp, slightly tart taste of wine on your palate. Too little acid, and your wine tastes flabby and non-committal. Too much acid, and your taste buds scream for relief. When acids are properly countered by the other ingredients in wine (such as alcohol, sugars, trace minerals, etc.), the wine is said to be "in balance", which is the desired end result of all winemakers.

Now that you know how acids impact a wine's taste, which acids are found in wine? Acids are present in wine in many forms, but the largest percentage of acidity (at least in wine made from grapes) comes from three primary types of acid:

• Tartaric acid
• Malic acid
• Citric acid

You may have seen or heard of a product called acid blend*, which is nothing more than a powdered mixture of the three acids listed above. If after conducting an acidity test of your wine, you discover that your wine lacks the correct amount of acid, the simplest solution would be to add an appropriate amount of acid blend to your must prior to fermentation. But we can't do that unless we know our desired acid levels.

Recommended Acidity Levels
Since each style of wine (red vs. white; sweet vs. dry) is made to taste different, it makes sense that each wine style would have its own range of recommended acid levels.

The chart below provides guidelines for acidity based on the type of wine you are making. Individual tastes vary, of course, so the information shown are recommendations only:

The numbers in the chart represent total acidity as a percentage by volume; winemakers refer to this as the titratable acidity, or T.A. for short.

If you're making wine from a grape concentrate kit like the ones sold on this site, you won't have to fiddle with measuring and adjusting acidity and pH. This has already been done for you by the kit manufacturer - the grape juice is already chemically balanced. On the other hand, if you make wine from scratch, read on to learn more...

There are two basic ways to measure acidity: measure it with a titration kit or a pH meter. Next, we'll explain how to perform each test.

How to Measure Acidity Using a Titration Kit
One of the simplest and most effective ways to measure T.A. in wine is by the titration method, which uses an inexpensive titration or acid test kit. These test kits can be purchased for as little as $6.00 and can be used over and over again.

If you took chemistry in high school, you'll probably remember that titration is a process where you determine the concentration of an unknown substance in a liquid (in our case, we are looking for the amount of acid in must or wine) by slowly adding a small amount of reagent (a base called sodium hydroxide - NaOH - whose chemical concentration is known) until a change in color occurs due to the presence of an indicator (phenolphthalein).

To begin the test, you will draw a 15 cc sample (one cc equals one ml) of must into a test tube. Most test tubes that come with the acid test kits are marked with a line indicating this volume. If not, no sweat. Just use a small plastic syringe (provided) to precisely measure the desired amount into the test tube, and be sure to rinse the syringe afterwards.

Next, put about 3 drops of phenolphthalein indicating solution into the test tube. Swirl or shake the test tube so the indicator is mixed in with the must.

Using the syringe, draw out 10 cc of reagent (sodium hydroxide), making sure there are no bubbles in the liquid. Be careful to avoid contact with your skin or eyes. This NaOH stuff burns something awful!

Very carefully, add the sodium hydroxide to the test tube 0.5 cc at a time. After each addition, swirl or shake the test tube to mix the contents together. You'll notice that the color of the liquid will momentarily change upon the addition of reagent. If you are testing white wines, the color change will be pink; if testing reds, the color change will be gray. Just swirl and swirl until the color subsides. So long as the color of the must goes back to the original color, repeat this step until the color change is permanent.

When the color (either pink or gray) DOESN'T go away, stop and determine the amount of reagent used. From here, it is very simple to determine the acidity of your must. For each cc of reagent used, this equals 0.1 % TA.

For example, if you used 6 cc of sodium hydroxide to react with the must, the titratable acidity of your must is 0.6 %.

Pretty simple, eh? Just remember to throw away your sample, since this stuff is toxic. DO NOT add it back into your must or wine.

Lastly, wash and dry your test equipment before storing it away.

If you ever run out of sodium hydroxide or phenolphthalein, just ask for Item #2717 or #2716P, respectively.

How to Measure Acidity Using a pH Meter
Measuring acidity in wine using a pH meter is very similar to the titration method explained above, but with a twist: Instead of looking for a color change (which can be very difficult to determine depending upon the color of your wine) to indicate the titration is complete, you simply add the reagent a drop or two at a time until your pH meter reads 8.2.

Why 8.2? This is the same pH at which phenolphthalein changes color.

If you can afford a pH meter (they can be bought for as little as $50 or so), this method is a much more accurate way to measure acidity than the straight titration explanation above. But pH meters are finicky things, so handle them with care:

• Don't drop the meter or otherwise damage the probe
• Keep the probe clean and free of debris
• Always calibrate your meter with fresh buffering solution before each test
• Be sure to stir the sample thoroughly after each addition of the reagent
• Store your pH meter in the manner recommended by the manufacturer, especially regarding the care of the probe

If you take good care of your pH meter, it should last a long time.

Adjusting Acidity Levels in Wine
Once testing is complete, you will know what your acid levels are. Compare this value with the suggested T.A. ranges in the chart shown above.

If you need to increase acidity:

• Add acid blend to increase acidity.
• 3.9 grams of acid blend will raise the acidity of ONE gallon of must by 0.1 %.

As a helpful hint for those who do not have scales, 1/4 teaspoon of acid blend weighs approximately 1.2 grams; a teaspoon weighs about 5.1 grams.

If you need to decrease acidity:

• Add calcium carbonate to lower acidity, but only to reduce acidity by 0.4 % or less.
• 2.5 grams of calcium carbonate (commonly referred to as chalk) will lower T.A. of ONE gallon of must by approximately 0.1 %.
• Alternatively, you can add a chemical called Acidex in place of calcium carbonate. Refer to the manufacturer's instructions for proper dosage.

One-fourth of a teaspoon of calcium carbonate weighs about 0.5 grams; one teaspoon of calcium carbonate weighs about 2.6 grams.

General tips:

• Until you get the hang of it, test your must twice to be sure of an accurate reading.
• If you need to make an adjustment to the must based on your testing, go slow and lean when adding acid blend or calcium carbonate (as the case dictates). You can ALWAYS add more chemicals to make further adjustments, but if you overshoot your mark it's difficult to take it out!
• Take a follow up sample to see how your adjustment went.
• Keep good records so you can duplicate or adjust future batches of wine.

*Many wine recipes call for the addition of acid blend during the workup of the must. The worst thing you can do is to blindly add acid blend (or any other chemical, for that matter) simply because a recipe calls for it. You should always test your must for acid and pH levels before you make any adjustments.