Just checking the 2009 Sandihurst Waipara Riesling for heat stability. Its a standard test that (nearly) all wineries do. Most white wines have Bentonite added to them in order to confer stability on the proteins found in wine. Unstable proteins, once too warm, give the wine an unsightly haze. .
Bentonite is a clay, basically an aluminium silicate, that when dispersed in water exists as minute flat plates. We add the Bentonite, in the order of 1-2g/L or thereabouts and mix the tank thoroughly. The positively charged proteins then attach themselves to the negatively charged and heavier Bentonite plates before falling to the bottom of the tank. We generally filter the now-stable wine to another tank. discarding the lees at the bottom.
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The test for stability used here is simple. A 0.45u filtered sample is kept in a water bath at 80C for 6 hours and then cooled/observed for haze. As seen above this Riesling, after an addition of 1.2g/L, still exhibited a little haze so will need more Bentonite added.
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