Last year, I had a stability issue with my 2008 Northern CA sauvignon blanc. It was crystal clear when I bottled (I swear--even filtered with a 0.5 micron filter), but as the summer progressed and temps in the basement cellar rose, some slight sediment fell out. Didn't affect the amazing taste or aroma, but the slight haze resulted in poor marks in the Winepress.US competition. The judges uniformly stated that without the haze, it would have been the Best of White by a long shot. Oh well, that's my bad. BUT--how to prevent this from happening again in the future???
The most likely conclusion that I've come to is a protein haze. My research tells me that Sauvignon blanc is notorious for protein hazes that form upon warming. These proteins are soluble at lower temperatures, but start to denature and precipitate as the temperature increases. A common preventative is to fine the wine with bentonite. The bentonite clay absorbs the soluble proteins and fall to the bottom of the carboy.
The main reason I've been looking into this is because I've got 15 gallons of 2009 Chilian chardonnay that I'd like to bottle soon. I had split the chard into 3 different 5 gallon batches to experiment with different yeasts, MLF, and oakings. Two carboys are crystal clear while the third is still a little hazy. I decided to do a light dose bentonite fining on the clear carboys for protein stabilization and a heavy dose on the hazy carboy for clearing & protein stabilization. Gets a little more complicated when one of the clear carboys has some lees at the bottom, so I have only had time to bentonite fine the other clear carboy. The other two will have to wait until after Christmas when I can rack them off the lees deposits.
That all said and done, I hydrated a 1.5 g/gallon dose of bentonite in 3/4 c of warm water--swirling like crazy and then letting the mixture sit for 24 hr. Only then did I pull some wine out and dump in the bentonite suspension and top off the carboy. After giving a good swirl to mix, the suspension has been slowly falling out over the past couple of days. I may have to bring the carboy upstairs to warm to room temperature before racking and bottling, but will see after Christmas.
By the way--the left over wine that I had to taste was AMAZING! Clean & crisp, with bright green apple & citrus flavors. Ooh, boy! Can't wait for this one!
a MA Winemaker