Potassium Bicarbonate is used in wine to help lower the acidity. 3.4 grams per gallon will effectively reduce acidity by 0.1%. You do not want to reduce the acidity by more than 0.3 - 0.4%.
Product as described.
I use a pH meter to check on the acidity and make sure the yeast aren't under stress. This is most common with cider and fruit wine making with RO water that has no buffering ability.
I use it to adjust my pH upward a little when my base is too acidic.
I have used this a couple of times on stuck ferments that get stuck due to high acidity levels (usually when doing fruit wines with acidic fruit). After adjusting temperature and stirring to re-suspend yeast, adding additional yeast and nutrient, I finally figured out that my must was too acidic. I added some potassium bicarb, and fermentation was rolling again soon. If your must has gotten too acidic, you may need to add fresh yeast after adjusting ph.