Controlling the acid level (or pH) during and after fermentation is another means to influence the flavor and character of your home brewed mead. Must should be slightly acidic since spring water should have a pH of 7 and honey has a pH around 3.9. Yeast prefer an acidic environment, but many other organisms don’t. This helps the yeast get a jump on other organisms that could ruin your mead or impart off flavors. Simple and inexpensive kits are available at most home brew shops that will contain everything you need, and teach you how to test for the pH level.
Tartaric, Malic, and Citric are the most common acids used to influence the flavor and pH of mead. Any combination of these acids can be used, and most acid blends sold contain a mixture of all three. Tartaric is the dominant acid in grapes, Malic is the dominant acid in apples, peaches, pears, watermelon, and bananas, and Citric is the dominant acid in lemons, limes, and many citrus fruits. Natural fruit juices also be used to influence acid levels. Each acid has a distinct flavor, experiment with them to learn which you like best.
There is some debate as to whether acid should be adjusted before fermentation or after. Must will become more acidic as the yeast metabolizes sugars. If the initial pH is too low, the yeast may stop metabolizing sugars, or impart off flavors as the pH continues to drop. On the other hand, if the starting pH is too high, the yeast may face increased competition from bacteria which can spoil the mead or impart off flavors.
Adding acid after fermentation is most often done to influence flavor, not the pH level. Since fermentation is complete, you are able to add acids or fruit juices to taste. Acids added after fermentation can help to offset the cloying sweetness of honey in a very sweet mead. Our Recommendation:
You should monitor the pH of the must before fermentation, but we only recommend adding acid if the pH is higher than 6.0. This is only slightly acidic which will benefit the yeast, but should not result in a very low pH after fermentation. Additional acids or fruit juices can be blended in to taste after fermentation. If adding fruit juice, make sure the yeast is inactive so that fermentation does not start up again.
There are pros and cons to both approaches, you should try both and see which method you prefer.