07 Jan Wintertime in the Cellar
I’m often in the cellar tasting through our wines in barrel this time of year to monitor the aging process. Part of the aging process is a secondary fermentation in barrel that dramatically changes the mouth-feel and perceived acidity.
Malolactic Fermentation (MLF) converts the harsher tasting malic acid to the softer lactic acid by a strain of bacteria called oenococus oeni. Fermentation is a loosely used term in this case as the process doesn’t produce alcohol, but it does give off Carbon Dioxide. It’s usually done on all red wines because the reduction in acidity creates a softer wine that doesn’t clash with the more pronounced structure and tannin.
Some whites are also run through this secondary fermentation (usually Chardonnay) to help lower the acidity and to create a rounder mouthfeel. MLF can sometimes add a buttery (diacetyl) character to the wine in some cases…..like Rombauer Chardonnay as an example.
During the winter I’m constantly sniffing barrels and listening for the tiny CO2 bubbles in barrel that let me know that MLF is still progressing. We’ll test each consolidated lot in the cellar to see how far along they are in the fermentation by using a spectrophotometerto measure how much malic acid is left in each barrel. It measures the light absorbance at 340 nanometers for each barrel sample and compares it to the light absorbance of a known standard. When the readings for malic acid reach less than 0.05 grams per liter then we’ll consider the MLF done.
While MLF is progressing the wine will taste a bit “buttery” or “yogurty” as the diacetyl is prevalent at this stage. Ideally the temperature should be around 70 degrees to push the wine through MLF in about 2 to 3 weeks. Cellar temps are a bit chillier than that and so it can take until spring for some barrels to finish.
After MLF is complete the wine is ready for a dose of sulfur to help protect it from oxidation and to keep it microbiologically stable. Before adding sulfur to the wine I first make sure that the diacetyl flavors have been consumed by the lees. If there is any diacetyl left the sulfur addition will keep the buttery character in the wine and that would be considered a flaw.
After the final dose of sulfur is added to the last barrel I can finally relax a bit with a glass of wine in front of the fire!