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?