I spent some time at a friends winery as they were barreling down at the end of harvest. I was lamenting the fact that I blew through the acid this year. It was spectacular fruit, but the pH was in the 3.7-3.8 range. She showed me their stash and said that folks without optical sorters always need to add acid to account for the potassium released from the stems even if they fully de-stem. Can’t catch all the stems and we should adjust for it. It was one of her tips, she said get more aggressive as I increase the whole cluster.
A few years ago, a different wine maker had told me that his commercial destemmer left 10-15% stems and he adjusted acid by 0.15 pH units in his Pinot to compensate for it. I ended up adjusting Cab and PS to 3.55 this year and after MLF, we are sitting in the high 3.6’s. So far so good.