This is my favorite time of year in the winery. The smell of fermenting grapes has engulfed the win ery while the musts quietly go through their transformation. As I look around the winery building I realize just how many changes we've made to our fermentation process and I thought I would share them with you.
In 2009 we picked nearly 5 tons of grapes which is a lot for us. Since we had such a bounty I thought it might be a good time to throw caution to the wind and let one of those tons ferment spontaneously while the rest I fermented as normal and pitched yeast (the safe route). It turns out that the "feral ferment" as it's called in Australia was by far my favorite tank and we have since stopped buying yeast. The modern winemaking process has the winemaker add a good amount of sulfite before pitching the yeast and this is done primarily to keep the wild yeasts and bacteria from starting on the grapes before the factory yeast has a chance to do its job. Purchased yeast has a very high tolerance to sulfites so it has no problem starting and completing the fermentation under those conditions. This is a very safe and sane way to make wine and has been the common practice in commercial wineries for some 50 years. In the feral ferment, the winemaker can't use as much sulfite (we want the wild yeasts to do their job after all) and this makes for a much more stressful process. At any time a rogue strain of yeast or bacteria can take over and create some really funky flavors and odors or even start the vinegar process. Careful attention must be paid to a feral must, but so far they've all gone pretty smoothly for us.
Incidentally, the addition of sulfite doesn't kill the wild microorganisms, it simply keeps them at bay for the duration the free sulfite concentration remains at a high level. Sulfite's power diminishes as the wine is exposed to oxygen and if it's not replenished those wild yeast and bacteria can get back to work spoiling the wine.
This year we introduced a new fermenter in the form of a terra cotta amphora and I don't know if I just wanted to do things as the Greeks and Romans did or if I just had a temporary moment of insanity, but I didn't add any sulfites. We can make a very good wine this way, but it's going to require that we harness the full antioxidative power of the grapes. I'll go more into that next time.