"Rene" wrote:

Metabisulphite, as a reducing agent may well have a precipetating
effect on certain proteins in solution. Alcohol in general also has a
precipetating effect on proteins (though generally in higher conc),
but together with the metabisulphide it may just about turn the cards.
It may explain the haze. Then, a gelatine fining simultaneously with
the metabisulphide addition after the last racking should get rid of
the problem.

A quick test you could try is to have a sample of your cloudy wine,
add some contact lens cleaner (containing proteases) and see if the
haze disappears.

Rene,

Thanks for the info, but I'm a little confused:

I think of precipitation as suspended solids dropping out of solution and
sinking to the bottom. Are we in agreement on this usage?

Do you mean that two reducing agents in combination may have the opposite
effect, i.e. to form a haze rather than cause precipitation?

If so, why doesn't this occur more frequently? Are there any predictable
(and thus avoidable) circumstances under which this might occur?

I'm now wondering if the two inexplicable hazes I've had in the past (with
apple wine!) have been a result of the S2O5 additions after all (although
they didn't occur in already clear wine, but rather the wine just failed to
clear without a great deal of fining).

Thanks.