Well bugger me sideways. I did a quick search before but couldn't find anything. I have since found this, which I have shamelessly lifted for ease of reference as it was in a long archive document from the HBD. It was written by Steve Alexander in 2002:
I've used campden tablets (a combination of sodium and potassium
metabisulphite) at around 1 to 2 grams in the mash for a 20L batch of beer.
This should produce about 40-80ppm of SO2. This seems like a *lot* of
metabisulphite to me, but it's below the levels used by winemakers. Campden
tablets are commonly used by winemakers to develop 100ppm of sulphite in
unfermented wine must.
I've only done this a couple of times - pils beers both times - and the
method produce a notably light colored beer with good flavor
characteristics. I haven't performed a controlled test of the method.
Only recently, as I prepared an talk for the recent MCAB did I come to
realize all of the advantages that sulphites bestow.
Sulphites -
- inhibit certain of the oxidase enzymes in the mash,
- prevent the Maillard processes and phenolic oxidation that lead to wort
darkening,
- mask the flavors of aldehydes,
- reduce the rate of lipid auto-oxidation and carbonyl formation.
They're a cure-all, and except that some people are allergic, can be highly
recommended. Yeast, particularly certain lager yeasts, produce some
sulphites during fermentation.
In the ASBC paper that Jim Adwell gave the web-link for the other day the
researchers added comparable levels (1.275gm of potassium metabisulphite to
15L of wort) at he beginning of the boil (the ASBC paper has several typos
btw), and the beer had lower trans-2-nonenal potential than a control and
higher levels (1.5ppm) of SO2 in aged beer, and according to the authors
"very good stability". They measure the results in terms of oxididation
products - oxidized polyphenols, oxidized sulphites(sulphates), carbonyls
and oxidized isohumulone.
Some of the same Belgian authors published a study in (JIBv105pp269-274,
Noel et al) in which they take a commercial beer and treat it with various
"stabilization" chemicals and then age the samples both naturally at 20C
and also at 40C with some O18 isotopic oxygen in the headspace. Cold-side
aeration.
Sulphite (13ppm of SO2) strongly protected polyphenols from oxidation.
PVPP treatment reduced the levels of polyphenols, but increased the level of
sulphite oxidiation.
Ascorbic acid additions caused a huge increase in sulphite and polyphenol
oxidiation ! The mechanism is the same one that is involved when reductones
from dark malt appear in beer. Ascorbic and reductones are anti-oxidants -
but if they are oxidized and given a tiny amount of Cu or Fe - then they
actually catalyze the oxidation reactions.