Acid testing.......?

This is an interesting question. Carbon dioxide in fermenting must will affect your acid titration. And, carbon dioxide in fermenting must will make it difficult if not impossible to accurately measure your sample. I suspose one could take a few ounces of fermenting juice and measure the volume. Then heat the fermenting juice to kill yeast and drive off CO2 that is present. If the heating evaporates liquid replace it with distilled water to the starting volume. Then test for acid as usual. One thing...during fermentation acid content will change. So, the acid reading you get may not be the starting value.

Bill Frazier Olathe, Kansas USA

Bill, Does the acid level always change as the must ferments? Does it increase or decrease? Do most folks adjust the acid level of their finished wine according to taste or the acid test after the wine is finished? thanks' James

james wrote "Does the acid level always change as the must ferments? Does it increase or decrease? Do most folks adjust the acid level of their finished wine according to taste or the acid test after the wine is finished?

During fermentation succinic acid increases but this acid is in very low concentration. Tartaric acid may precipitate out of solution as the fermentation goes along especially if temperature is cool. Malic acid can be changed to lactic acid by ML bacteria and this will lower the acid concentration. But my experience is that acid concentration tends to decrease over all when fermentation is complete.

Use your taster first to decide if the wine has too much acid. If it's too tart, depending on the wine, you can add a little sugar. If it's really acidic tasting do titrations to find out how much acid is in the wine and to guide you on acid removal. If it's flat tasting do titrations so you know how much acid can be added without over doing it.

Bill Frazier Olathe, Kansas USA

If you have a malo-lactic fermentation going at the same time as your primary fermentation, the total acidity will change as the fermentation progresses. You can sometimes end up with malo-lactic fermentation occurring without intending too, since the bacteria responsible can be natrually occurring. So, while you could get an accurate acid reading for that particular point in the fermentation, it may not be "accurate" in the sense of being stable over time.

I don't believe there's anything about the yeast fermentation process itself that would cause a problem for determining total acidity by titration, or with determining the pH with a pH meter.

However, if you are titrating and looking for a color change, that will probably be easier after fermentation has completed and the wine has cleared. If you're looking to maybe adjust the acidity by beginning a malo-lactic fermentation, however, you may want to determine the total acid level prior to the end of yeast fermentation, as the malo-lactic bacteria like grape skins and other nutrients in the must as well as the heat generated from the yeast fermentation. You can start the malo-lactic fermentation later after the yeast fermentation has completed, but you may want to also add some malo-lactic nutrient to help get it going.