2009 Wine Harvest

The 2009 harvest has arrived! I picked up three 5.4 gallon buckets of California grape juice this past weekend, which will make about 80 bottles of wine. I had my heart set on a petite syrah and a tempranillo, but you need to adapt to the vagaries of the harvest and delivery schedule. So I ended up with a barbera, a sangiovese and a sauvignon blanc. I've done a lot of wine making in my life, but this will actually be my first white, not counting mead!
The barbera had an original gravity of 1.092, the sangiovese 1.100 and the sauvignon blanc 1.102. Assuming these all ferment to dryness, this should yield alcohol by volume of 12.2%, 13.2% and 13.5% respectively.
How does all this abstruse alchemy work? It's not that complicated. Wine makers and beer brewers all use a tool called a hydrometer. This a weighted glass measuring tool that floats in the wine must or beer wort (or in a cylinder for ease of measuring). Depending on the specific gravity of the liquid, the hydrometer will float or sink to a measuring line on the instrument. You can thank Archimedes for this neat trick!

So what is specific gravity exactly? Well it is the ratio of the density of the liquid to the density of the water. The gravity of water on the scale is set to 1.000. The suspended substance that increases the density from 1.000 to 1.100 or 1.102 is comprised almost exclusively of sugar. The yeast will consume the sugar and as a by-product will produce alcohol and carbon dioxide. The resulting alcohol will have a gravity similar to that of the water and therefore you can take another gravity reading (the final gravity) and can calculate the amount of sugar consumed and hence the amount of alcohol produced. You can calculate this yourself, but there are lots of web calculators that do all the fancy math for you. Remember to keep track of the temperatures as well, as the gravity of the beer or wine will change as the temperature increases or decreases away from the default value of the hydrometer, usually like 60 degrees Fahrenheit.

There are several other methods of calculating sugar levels in wine. You often hear the word "Brix" used in wine making, which is similar to gravity, but more precise because it measures sugar levels by the refraction of light as it passes through the liquid, as compared to pure water. Vineyard owners like this tool because they can squish a single grape in the field to test sugar levels and determine the perfect time to harvest their grapes.

Stay tuned for more info on fermenting and aging of the 2009 vintage!