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Why are my TA readings off?

TroubleShooting

Bernie Andreoli — Old Forge, Pennsylvania asks,
Q

I crushed and sulfited my Cab grapes. In doing the initial tests I got the following readings. Brix was 23.5 (+.22 temp correction) = 23.7, S.G. 1.099 (+.013 temp correction) = 1.112, TA = .60 g/100 mL, pH = 3.02, Temp = 75 °F (24 °C) In the last WineMaker contest all the judges said my wine lacked some balance and finish. I wanted to raise the acid level to .70 g/100 mL to help with the balance and finish but I am afraid the pH will go too low and prevent the survival of the yeast. I used the Vinoferm test kit for the TA and have a digital Omega 3+ pH meter for the pH. I calibrated the meter with a 7.0 NIST buffer prior to starting the measurements (the wine shop was out of 4.01 buffer packs). I took the readings 3 times from three separately retrieved samples. I also took three samples to test the TA and besides the color change indication, I tested the samples post color change for neutral pH of which I got readings of 6.98, 7.01 and 7.13 g/L so I know I was very close. I am going to add the yeast (Premier Cuvée) so I don’t expect resolution for this dilemma prior to this year’s batch, but hope to gather info in case it happens again in the future. My thought is since I am in the TA range for a red wine, although at the low end, I am going to inoculate without any acid additions. I find this a little strange since in all the prior years I’ve had to push the acid up to get it into the range. The grapes are from St. Helena, California.

A
I have to hand it to you for doing such complete analysis on your must. If every winemaker were as conscientious as you are, we’d have fewer stuck fermentations, sluggish malolactic fermentation bugs and unhappy yeast beasties. I think you made the right choice to not add any acid to this batch. As you mention, your pre-fermentation TA is already around 0.6-0.70 g/100 mL, which is definitely in the red winemaking sweet spot, especially for Napa Valley Cabs (St. Helena is a small town at the northern end of the Napa Valley). The pH that you report is a little odd though and gives me pause. With a pH that low (3.02) one would expect to see a corresponding TA in the realm of 0.80-1.0 g/100 mL as opposed to the more reasonable, lower levels you saw. My suspicion is that you already pointed out the source of this weird parameter – the fact that you only standardized your pH meter with one of the buffers, the pH 7.0 buffer. When using a pH meter (a great tool for serious
Response by Alison Crowe.