One of the biggest consumers of my time during crush is sampling winegrapes. A couple of times a week I jump in my Passat - rather than the standard winemaker-issue white pickup truck - and make the rounds of all our vineyard sources, from west Lodi, to Clements Hills, on up past the Sacramento County line.
Though many winemakers prefer to fill a 5 gallon bucket with whole bunches of grapes, I like to walk along the row or two we'll be harvesting, randomly grabbing two grapes every few steps. One grape goes in a Ziplock baggie, the other into my mouth. Once I've got a hundred in the bag, I squish 'em and I'm done.
I try to get a feel for how the flavors of the grapes differ from one side of the vineyard to the other. In my mind I can taste the perfectly ripened grape as having a certain richness and complexity of flavors. If the grape tastes like boring, tart water, it's not close to being ready.
Though I tend to look for that certain typical Lodi jammy deliciousness, if all I get is raisin, I've failed. You could pay $15,000 for a ton of Rutherford Napa Valley Cabernet Sauvignon or $700 for Lodi Zin, but if the grapes have raisined, both wines will taste like the same alcoholic raisin juice.
Some other factors I consider are the acidity (pH) of the juice from the squished grapes as well as the sugar level (Brix). Browning of the seeds is also important as an indicator of ripeness and a predictor that the tannins won't be as harsh.
All this work is to make the absolute best decision as to which day to pick those grapes, because once they are cut off the vine, whatever flavors are present will be locked in. (Grapes don't continue to ripen as peaches do.)
In cool seasons like we're experiencing this year, the margin for error is forgivingly large. During warmer seasons even one day can make an obvious difference to how the wine will turn out. So figuring out which day to pick is probably the most important decision a winemaker will make.
Last Friday, 9/10, I followed Borra's winemaker Markus Niggli as he was getting a feel for ripeness in Gewürztraminer he'll be taking from Mokelumne Glen's river-side vines in Victor. Our conclusion was that the grapes just needed a bit more flavor, but were looking good.
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