At the end of the harvest season...
Almost all of our grapes are harvested now and we are at the end of a long period when I spend a lot of time monitoring the grapes' sugar level. Starting in July when veraison (see my blog from July) occurred we started testing Chardonnay grapes destined for sparkling wine. Sugar levels rise very fast after veraison and we went from 5 Brix (percent sugar in a grape) to 14 Brix in 3 weeks. Since we pick those grapes somewhere between 17 and 19 Brix we have to start checking more frequently at that point.
We harvested the first Chardonnay on August 18, and after fermentation the wine is now waiting to go through a second fermentation in Champagne bottles later in the season.
Depending on the wine you make you aim for different sugar levels. As an example I like Sauvignon Blanc grapes to be around 22.5 Brix but for red varietals I am looking for around 24-25 Brix. On Monday when we pick the last grapes, Cabernet Sauvignon, it will be 8 weeks since the first grapes came in. And no more sugar analysis in the field. The refractometer for measuring sugar which I carry around all the time can now get a rest.
But sugar is just one aspect. Acidity is just as important and it decreases at the same time as sugar levels go up. While the sugar becomes alcohol during fermentation, the acidity stays in the wine and is both a great flavor enhancer and preserves the wine as it ages. I like to pick grapes at the lower end of typical sugar levels which keeps a little more acidity in the grape and makes for well-balanced wines.
However, the most important aspect in deciding when to pick the grapes is still taste. Our taste buds are fine instruments which are easy to bring along. I taste the grapes and look at the color of skins and seeds. Seeds go from green to brown, they lose some of the bitterness and the flavor of the grapes become more complex. At the end of the day the subjective taste of the winemaker is the most important measurement.