"steve" wrote in message
...
Hi folks,
I am seeing something that I thought was really only a problem with beer
making - specifically that when I put my 2003 French colombard in the
fridge
it gets cloudy. Just like a chill haze in beer. This wine is crystal clear
at room temperature, and was filtered prior to bottling, but definitely
develops a haze when chilled.

Anyone seen this before? or have an idea what might be going on?
thanks - steve in vancouver

Steve,
Grapes contain tartaric acid potassium. Potassium reacts with tartaric acid
and forms a material called potassium bitartrate. Potassium bitartrate is a
clear, crystalline material. Cooks usually refer to potassium bitartrate as
cream of tarter, but most winemakers call this material "tartrate."
Potassium bitartrate has several interesting physical properties. (1) Only
small quantities of this material can be dissolved in grape juice. (2)
After grape juice ferments and alcohol accumulates, even less potassium
bitartrate is soluble in the water-alcohol mixture. (3) The quantity of
potassium bitartrate dissolved in wine is strongly dependent upon
temperature, and cold wine cannot hold as much potassium bitartrate as warm
wine.

Generally, grape juice contains all the potassium bitartrate it can hold
when the grapes are picked. Alcohol begins to accumulate when the grapes
are fermented. As the alcohol concentration increases, the new wine becomes
saturated, and potassium bitartrate precipitates out of the wine. As
fermentation continues, more alcohol is produced, and more tartrate is
forced to precipitate out of the wine. So, new wine is over saturated with
potassium bitartrate when fermentation is complete, and the tartrate
continues to drop out of the solution. However, tartrate precipitation is
very slow at normal cellar temperatures, so potassium bitartrate causes
serious long-term stability problems for the wine industry.

The following example illustrates a common tartrate stability problem. A
new white wine is clarified and aged for several months. The wine is then
filtered with a 0.45-micron membrane and bottled. The newly bottled wine is
clear and bright, but the wine is still nearly saturated with potassium
bitartrate. Ultimately, a consumer puts a bottle of this wine into a
refrigerator for a few hours before it is served. The wine cools rapidly in
the refrigerator, and potassium bitartrate precipitates out of the cold
wine. (See property number three above).

As tartrate drops out of solution, suspicious looking crystals are formed in
the bottle, or haze forms. Tartrate hazes are very unsightly, and sometimes
the consumer mistakes the tartrate crystals in the bottle for glass
particles. In any case, the consumer is unhappy, and the winemaker is
embarrassed. All commercial white and blush wines are cold stabilized (held
just above freezing for several days) sometime during the winemaking process
to remove the excess tartrate material before the wine is bottled.