Our first harvest of the season at Three Fox Vineyards in Delaplane, VA occurred on Friday September 7th. It was a beautiful day, but the remnants of some tropical storms were supposed to blow through later that weekend, and we wanted to get the fruit off the vine before that happened. The last thing you want to have happen right before harvest is a big rainfall: the vines suck up the water and pump it into the grapes, effectively diluting their flavors at best, and possibly even bursting the fruit on the vine and losing crop. We had tested the fruit just a few days prior (more on that in a sec) and knew we were within the "harvestable" window, so rather than take the chance with the rain we decided to harvest perhaps a few days before what may have been the optimum time. This is not at all unusual, as especially in Virginia you are at the mercy of fickle weather systems and must adapt your harvest schedule appropriately.
Determining When to Harvest
To understand the decision of when to harvest, you need to know a little bit about how grapes grow and ripen. From the perspective of a winemaker, grapes go through two phases: an initial growth phase, during which time the berry size steadily increases, and a following ripening phase during which berry growth slows, sugar levels start increasing and acidity starts dropping (pH increases) [Ignore the anthocyanin in the cool cool graph I stole from the Texas Cooperative Extension page]. The transition between these two phases is called veraison - this is a French term which means "change of color of the grape berries". The berries start softening, and their color starts changing from fresh growth green to the color appropriate for their varietal (i.e., "red wine grapes" start getting reddish purple, "white wine grapes" start getting yellow-gold). Shortly after veraison is when you want to start taking readings of the sugar levels in the grapes to gauge how the ripening process is progressing.
Sugars levels in a liquid is measured in brix. The unit of measure- ment for brix is "degrees", so when you take a brix reading of the grapes, you'll record a result of something like "19.5 degrees brix". To take a brix reading of the grapes, you first walk around each "block" of vines (Three Fox "blocks" are 30 rows long) in the vineyard, and take a random sampling of 15 or so grapes. This random sample should include grapes from the beginning, middle and end of the vines, as well as from both of the East and West facing sides of the vines (Three Fox rows are oriented N-S). You then allow the grapes to rest a bit, and cool down to 65 degrees F or so (winery temps). Then you mash them up and use a refractometer (or fancier instrument, but a refractometer gives you a precise enough reading at this point) to measure the brix by placing a couple drops of the juice on the plate and looking through the viewer and taking your reading.
So, we had done this with our Viognier and Pinot Grigio a few days prior, and knew that we were within the "harvestable" window in terms of brix levels (I don't have my notes, so I can't tell you exactly what the brix levels were, but they were in the low 20s). Thus we decided to harvest the fruit before a possible storm could negatively affect their quality.
Next Up: Harvest and Crush
I think this has been a rather scary post for the non-technically inclined, with lots of weird terms like "brix" and "refractive index" thrown into it, so I'm cutting this one off. My next post will detail the harvest, crush, press and yeast addition to start off the fermentation of the Viognier and Pinot Grigio, and will have cool pictures rather than boring graphs!