The ideal time to test and adjust acidity of red wine is just after grapes have been pressed to form the must, but before fermentation has begun. Having optimum acid levels will yield a better fermentation. T.A or titratable acidity is a measure of total acidity by measure of volume. For a dry red wine the range is .60%-.70% T.A., and for a sweet red it is between .65% and .80%. Commercially available titration kits are the the simplest and most effective method of testing your must. They are inexpensive and can be reused.
You should begin by collecting a testing sample of 15 cc or milliliters of your must. The units are interchangeable, it just depends on what scale is being used by your kit. Add the indicator, generally phenolphthalein, according to the kits instructions. For this next step, it is important to work slowly. Add the reagent, often sodium hydroxide, using the provided syringe. Go slowly, adding one ml at a time, stopping in between to agitate the test tube until the color returns to normal. When the color change is permanent you can your T.A based on how many milliliters were used to reach that state. Six milliliters of sodium hydroxide equals a T.A of .6% for example. After testing, dispose of your sample. Do not pour it back into your must, the sample will be toxic.
Now that your must’s T.A is known, adjustments can be made as needed. Too much acid is generally countered by adding calcium carbonate. 2.5 grams of it will lower the T.A of a gallon by roughly .1%. Commercial acid blends can be used to increase acidity, 3.9 grams generally raises the acidity of a gallon by .1%. Whenever you are adjusting acidity, dissolve the additive in a little bit of wine first before adding it to your must. Adding it directly requires vigorous mixing which will expose your must to excess oxygen. Go slowly and measure carefully. Once the desired level is reached, your red wine is ready to ferment.