Saturday, 22 February 2014

Subzero Chills

I really thought things were getting cold enough when we started killing ferments by reducing the temperature to 5 degrees (see post on 'chill kills' it turns out these are really minor chills in comparison to the technique of cold stabilisation.

There are a number of white wines that are now in their final stages of production and it is important to ensure they are ready for bottling and sale.  Clarity of the wine (or limpicity, if you like wine-geek terms) is considered a very important aspect for the consumer, so winemakers want to ensure that there are no unstable compounds that may precipitate out of the wine whilst it is in the bottle.

The most common compound to precipitate from wine is potassium bitartrate (cream of tartar), which is present in the wine due to the high levels of tartaric acid found naturally in grapes.  Interestingly enough, the tartrate crystals that can form are actually quite harmless, it is primarily for aesthetics that they must be removed.  Consumers may mistakenly identify tartrate crystals as glass or other foreign particles and consider the wine undrinkable.

Potassium bitartrate crystals will precipitate out in greater quantities as the temperature is decreased, therefore to be absolutely certain that enough crystals have been removed, the wine is chilled right down to -2 degrees.

It is possible to determine roughly when subzero temperatures have been reached because the door of the stainless steel tank will be frozen over!  The photos below were taken when the chill had reached 2 degrees.

the chiller - frozen over!
the tank of wine being stabilised