Wednesday, October 7, 2009

The first fermentation of 2009!

The first fermentation for the 2009 VELLUM is underway!

A few days ago we inoculated the must of the Petit Verdot and today the yeast have been multiplying quickly eating up the sugar in the grape juice. Unfortunately however the lifespan of a yeast cell is short-lived. Sometimes it is no more than a few days, but that is all that may be needed. Their purpose to winemakers is deceptively simple: consume sugar to make alcohol.

Although in most red wines it is ideal for stability as well as style that the yeast which began the fermentation consume all of the sugar before their population dwindles and eventually passes on - - in reality, a complete fermentation takes great planning, control and mindfulness.

It is very important too that all of this takes place in lower threshold but persistent temperatures (78-82 degrees F). In this environment the yeast may still thrive and produce its own heat but the wine greatly benefits by having its fruit and varietal character preserved. Here, a successful fermentation is quantified in very small fractions of a percent of residual sugar.

Right now the Petit Verdot is at 79 degrees F and about 6 Brix (measurement of sugar content) but on Saturday afternoon it was at 24.1 Brix. A typical fermentation does not move at this rapid speed considering that it is fermenting at a lower temperature.

Yeasts can perform in a wide range of kinetics where some metabolize sugar slowly as their population multiplies and lives longer and others may build up their population and consume sugar until they die quickly from the rising alcohol level.

The yeast chosen for the Petit Verdot was neither, however in this situation it performed like the latter. So what is important to realize here is that the right yeast was chosen for the job as well as a proper fermentation strategy.

To further aid the yeast, tomorrow the second of a process called a "delestage" will be performed. Here all of the wine will be removed from the tank and and then returned over the top of the grape skins and seeds gently. The intent of this process allows the yeast to obtain as much oxygen as possible to help live through this difficult stage as their food source depletes and environmental conditions worsen.

Eventually, this fermentation will become "dry" when the sugar level is so low that it can no longer be considered a viable food source and the yeast will pass on - leaving our wine in its wake!

- Karl Lehmann


Anonymous said...

The explanation for the fermentation process is some of the best writing I have ever read.

Kudos to the winemaker!

Anonymous said...

Your blog keeps getting better and better! Your older articles are not as good as newer ones you have a lot more creativity and originality now keep it up!