Lifespan of sodium metabisulphite

[Josephine Dakin]

Hi All,

How long does sodium metebisulphite last?

I foolishly bought a BIG bag from Vigo last year. As I was using it, the remaining powder in the bag absorbed water from the surrounding and somewhat humid atmosphere. It went rock hard. I then broke it up into pieces (yes, that hard!), and shared it out among several food-safe, airtight bags.

Do you think it's still as efficient to use as it was when I bought it? Or should I get new for this year's production?

Many thanks,

Jo

--
Jo Dakin
The Little Orchard Company
www.thelittleorchardcompany.co.uk

[Cheshire Matt]

Metabisulphite does degrade over time - if you search on here you will find
Andrew Lea explaining the rationale behind his dosage rates compared to
what Vigo may publish. Sounds like your batch is shot - or at least been
stored in a far from ideal environment. So for what sulphite costs, say in
comparison to a brand new vigo belt press, I'd buy some more just to ensure
all the effort expended on pressing is not wasted. But that's just my
view.

I also tend to buy sulphite/camden tabs from my local homebrew shop and
support local. It's widely available, and a commodity, so really can't see
the point buying from Vigo.

[Andrew Lea]

A
On 26/08/2012 14:10, Josephine Dakin wrote:

>
> How long does sodium metabisulphite last?

That is impossible to answer. It is not of fixed stoichiometric
composition wrt SO2 even when fresh. And it oxidises with time and humidity.

If you have a large bag and want to continue to use it with confidence,
and you are comfortable with doing and calculating titrations, the best
thing is to make up your standard 10% solution (5% nominal SO2) and
measure its strength by an iodine titration. Then you can adjust the
dose accordingly. You would need to repeat the titration every 2 weeks
or so.

Otherwise as Matt says, buy smaller amounts locally for each season, and
assume a 50% yield of SO2 (the stoichiometric yield for NaMS is around
60% AFAIR so I err on the side of caution and to make the figures easy
to work with).

Andrew


--
Wittenham Hill Cider Portal
www.cider.org.uk

[Tim]

Always buy mine from local brew shop, cheaper, readily available and I
always get a good chat with the owner. :)

Tim

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[Josephine Dakin]

Thanks everyone. Gonna get some new. Unfortunately, we have no homebrew shop for about 30 miles.