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Crazy pH Shift


Al Basiulis — San Pedro, California asks,

I purchased Pinot Noir grapes from Santa Ynez, California. The crushed grapes readings at harvest were 3.35 pH and 24.5 °Brix. When the grapes arrived at our location we confirmed those readings then put the crushed grapes in A cold room for four days. After the first day, the air conditioner (A/C) started to lose power and the room hit 70 °F (21 °C) for two days. By the time we discovered this fact, the natural yeast had taken off and reduced the must to 10 °Brix. At this point we added Lalvin BRL97 to finish fermentation and moved it on to malolactic fermentation (MLF). Two weeks later we picked up Syrah grapes with a pH reading of 3.55, which we again confirmed locally. The A/C was working this time so we were able to use our traditional yeasts we use for Syrah while the must was still at 24 °Brix. After fermentation we also put the Syrah through MLF. The pH of the Syrah was now 3.73. Unlike the Syrah, the Pinot pH has gone from 3.35 to 3.94. I checked my pH meter by checking against a cream of tartar solution (3.52) before testing the Syrah (3.73) and Pinot (3.94). I had consistent results over 3 different occasions so I have to believe the readings are correct. Any thoughts as to what would have caused such a dramatic shift in the pH? the native yeast?

I applaud you for trying fresh winegrapes in your home winemaking, you’re lucky that you are (relatively) close to a fine winegrape growing area like the Santa Ynez Valley. I grew up just down the California coast from there and one of my first harvests was at Curtis Winery in the area that at the time had its own estate vineyards containing Pinot Noir and Syrah. My current company grows many acres of Pinot Noir in Santa Barbara County and it continues to be one of my favorite grapes to work with. The data you report for your Syrah is extremely typical. Syrah tends to come in quite high pH after MLF is complete, so your 3.55 to 3.73 shift is entirely normal. In fact, I’ve seen Syrahs with a 3.55 starting pH register in the 3.90s after MLF so 3.73 isn’t that high and is in fact quite a good number. Your situation with your initially acid-balanced Pinot Noir (pH of 3.35 at 24.5 °Brix), in contrast, is indeed a strange one. Having a starting pH of 3.35 in
Response by Alison Crowe.