Sodium Met - Prevention of oxidation

[MARMITE]

I was re reading GW's book Home Brewing The Camra Guide page 122 and see that S Met is used as a preservative in beer as an antioxidant. Does anyone add this to their beer as a matter of course as a precaution against oxidation and how much do you use ?

[steve_flack]

I don't add it to my finished beer but I've seen it being added to casks at a commercial brewery (Palmers in Dorset). They were adding a Metab tablet to each cask at racking. I'm also aware that you can add it to the mash to reduce oxidation there - 20-30ppm of Potassium metabisulfite is the suggested dose. One campden tablet gives about 50ppm per gallon (as the sodium salt).

EDIT: Isinglass finings are preserved with sulfites AFAIK so maybe I am adding sulfites indirectly.

[MARMITE]

Thanks for the reply steve. I dont understand why oxidation is a problem in the mash. surely the boil will eliminate any air and then we need to admit air for the fermentation.Am i missing the point.?

[Aleman]

oxidation does not have to involve air, merely the transfer of an electron from one chemical to another (Or going the other way the transfer of a proton from one chemical to another) One of the chemicals is reduced and the other is oxidised.

Is this a problem in the mash?? It could be.
Are we as home brewers likely to see it? It might be possible, it can show up as a loss of hop flavour and at very low levels is quite subtle, it is also not likely to show up except in long term storage. From the reading I've done over the last couple of years it also appears to be more possible in 6 row barley than UK 2 row.

Why should we be concerned? Should we? The mash absorbs an incredible amount of oxygen from the airspace above it, and this is 'stored' in the wort and beer as time progresses chemical changes take place in the beer, and the electrons start to get passed from chemical to chemical (Oxidation happens). If you can provide an alternative pathway for the oxidation to take (i.e supplying sulphites) then you can reduce the effects of oxidation.

In the UK commercial brewing environment, little is done to minimise the effects of oxidation on the mash . . . but then the trade is a running one. There is a lot of effort to reduce post fermentation exposure to oxidation as this has a significant effect on flavour in the short term.

[MARMITE]

Thanks for the reply but am still struggling to get my head round it .Would it be helpfull to add say 1 tablet to the brew prior to bottling, for insurance ?

[Aleman]

Not really,

When I was bottling I would swill some Sodium Metabisulphite solution around the bottle and allow it to drain. The residual liquid would contain some.

TBH it is more important to have a good brewing/fermenting/bottling technique than it is to mess about with additives which may or may not be required / do anything!

[TC2642]

Not really,

When I was bottling I would swill some Sodium Metabisulphite solution around the bottle and allow it to drain. The residual liquid would contain some.

TBH it is more important to have a good brewing/fermenting/bottling technique than it is to mess about with additives which may or may not be required / do anything!

Agreed, you only need a residue of Sod Met. to be effective in reducing oxidisation, adding a whole tablet at bottling may give suphury notes to the final beer.