Just days now before the Sauvignon Blanc comes in. Our small section, as well as Lail and Honig wineries' sections, the fruit is definitely sweet enough to make great wine, but the acids are still a little high. For our wine, which is made in a clean, fresh style, we try to pick as soon as possible to keep the alcohol low and the acid relatively high. Now, that said, it's pretty easy to pick too early if you just look at a sugar sample. While I send Brad, my assistant, out to get berry samples and run the numbers, I primarily look at the pH to see when the trends show a big change in direction. Simply put, a lower pH means higher acidity (pH is the inverse logarithm of the concentration of acid, a combination of tartaric, malic, and a few others). As grapes mature, they use up the malic acid and the acidity goes down and the pH rises. If you plot the pH on a line over the sampling season, it suddenly takes a turn which, in my view, is where one enters the window of ripeness. It then becomes stylistic and discretionary for when to harvest. Back to the Sauvignon Blanc, I try to pick early on in the ripeness window but not too soon which would lead to a too-tart wine.
The trick here is to make sure it's not too early and a field sample is only as good as the skill of the person sampling. I'm always drumming on Brad to "sample the juice," meaning, "don't sample what looks good to eat (a natural reflex), but instead represent what will come in to the winery." That means you have to find all the clusters hiding in the canopy, which, for Sauvignon Blanc, is quite bushy. If the field sampler can't find it, the pickers surely will.
As an insurance policy for harvest timing in our Sauv Blanc, I always make a point to go out in the block and literally stick my head deep into the canopy and look around. I look for the greenest clusters in there and taste a few berries from those clusters. They represent the tail end of ripening and when THOSE berries taste in balance, we pick ASAP. Note that I wrote "taste," not "measure" because, in the end, that is the winemaker's ultimate tool. I'm sure we could measure just those tail-end berries for pH (forget sugar) and get a verifiable result, but why bother? As my French counterpart said to me when we had a translation issue, "it's the taste." Kinda cool that we have these measuring devices built-in, wherever we go (unless you have a cold).