rethinking acid corrections

Assuming that your measurements are accurate, you are probably overestimating that liquid volume of your must. You need to subtract about

15-25 % from the apparent volume in the primary (the exact figure depends upon the size and condition of your grapes).

One way to handle this is to add HALF the tartaric acid indicated, stir, and retest the must. If you achieved half the adjustment you calculated, you can safely add the same quantity. If there is a discrepancy, adjust the additional amount you are adding accordingly.

That makes sense, but on a really simplistic basis, when you taste a fresh grape, the juice tastes sweet and the skin tastes tart. That must mean that when the juice and skins are fully fermented, the resultant must is more acidic than the starting juice.

Lee

That also makes sense, but .... try the same test after 24 hours of fermentation (or cold-soaking), and you will see that most (if not all) of the tartness (but not tannin content) has been adsorbed by the liquid must.

Sorry, but that's not right. The juice tastes sweet, but the skin tastes _tannic_. When the fermentation starts to break down the skins the pH goes _up_ because of the release of potassium therein.

At the end of fermentation, the wine may taste noticeably acidic, but that's due to dissolved CO2. That goes away with either barrel aging or degassing, and ML fermentation will further reduce the wine's acidity.

Tom S

Tom, of all contributors to this newsgroup, your comments are always helpful and accurate, and I wish you lived next door. But I'm still confounded why I get such screwy discrepancies when I test a freshly crushed must versus when I wait for 4-5 days of fermentation. I virtually always see lower pH's after 4-5 days, and the TA's are often higher. I'm getting to the point where I think my acid corrections are hurting more than helping.

Lee

If you failed to degas your sample taken during fermentation it may very well read higher TA than initially. I'm not sure about the pH going down for that reason though. Try bringing your samples just to the boiling point to drive off the dissolved CO2 before you run your measurements and see if that helps.

BTW, when doing an acid addition always try it on a small sample first and _taste_ it as a sanity check.

Tom S

Lee, are you saying that you see these type of changes even if you don't make any acid corrections, or that the numbers you measure after you make an acid adjustment are not what they should be 4-5 days later?

If the latter then you have to think about what Negodki said about over or under-estimating the amount of juice you have in your must. Are you taking measurements right after your adjustments as well or just 4-5 days later?

If the former, then something else is going on.

Lee, as Tom says, at 4-5 days of fermentation your wine is going to be high in dissolved CO2 which means carbonic acid in your wine which will both raise TA and lower pH. So that's a very difficult time to make reliable measurements of either. As Tom also says, if you want to try to measure either TA or acid during or just after fermentation, you need to take measures to degas your sample, by boiling and/or shaking vigorously. Your apparently increased acidity may well have something to do with dissolved CO2. All of the advice you've gotten on taking care with additions is good, though - whether it's sugar, SO2, acid, or anything else, putting it in is a lot easier than getting it out ;^)

- Mark W.