In my last blog on processing the grapes I took you through the crushing/destemming, pressing, allowing the resultant juice to settle overnight, racking the semi-clarified juice to individual carboys, testing, chaptalizing, and adding nutrients. I then transferred all the white grape juice filled carboys down to my wine cellar where the temperature was between 55 °F and 60 °F. Meanwhile I left all my reds in the garage at a warmer temperature to start their fermentation. But why bring that white juice to the wine cellar to start fermentation there instead of the garage? It comes down to trying to bring out and maintain the fruity aromas that are so sought after in white wines.
In commercial wineries bright, crisp, and fruity white wines are typically fermented in stainless steel tanks that have a temperature-controlled jacket that encircles them. That temperature-controlled jacket is utilized during fermentation to maintain a consistent relatively low temperature in order to maximize fruit aromas and flavors – around 55 °F. If you fermented your white wines at significantly higher temperatures, all those wonderful peach, pear, pineapple, apricot, and citrus aromas and flavors would be lost. Unfortunately, as a home winemaker, I don't have access to temperature-controlled tankage. So, I compensate with cooler ambient temperatures that happen to exist at this time of year in my wine cellar. As my white wine fermentations all take place in 5- or 6- gallon carboys, they are small enough volumes that the heat produced in the fermentation process is easily dissipated by the lower ambient wine cellar temperatures. This works to allow me to bring out all those non-grape fruit flavors that make white wines so special.
A shot of my Vidal Blanc at harvest.
Once I have all my white wine carboys set up on the benches in my wine cellar, I prepare my yeasts as per the re-hydration instructions on the packets. I then add the yeast to the carboys and provide a good mix. Each then gets fitted with an airlock and I await the beginning of alcoholic fermentation. This is the process by which sugar from the grape, and the added cane sugar from chaptalization, is converted biologically to alcohol and carbon dioxide. The airlock allows the carbon dioxide to escape while keeping air out. Air, especially with white wines, can be a formidable enemy. Air can cause oxidation — browning and off-flavors — as well as allow for unwanted aerobic organisms — acetobacter — to gain hold and turn your potentially wonderful wine into a wonderful salad dressing!...