On Fri, 2 Jan 2009 01:39:16 -0800 (PST), Joe Sallustio
> wrote:

>Campden tablets are premeasured amounts and can be made with either
>sodium or potassium, if used crush first. I prefer potassium
>metabisilfite (K2SO4) as it is easier to use and cheaper. 5 campden
>tablets = roughly 1/4 teaspoon K2SO4 as I recall which works out to
>40 to 50 PPM free sulfite addition in 5 gallons (US) of wine.

E. C. Kraus sells a 1/16 teaspoon measure for bulk potassium
metabisulfite. Each measure is supposed to equal one tablet. It's a
lot cheaper that way. One tablet per gallon initially (and at each
racking and bottling time if you prefer) usually does the trick, and I
think it puts it at 60 ppm. I only use it initially but most recommend
using it at each stage. I have a family member who gets sick with
sulfites and I am somewhat sensitive to it myself (asthma).

If you only use it at the beginning, it's undetectable by the end of 3
months in the fermenter(s). If you skip using it at any stage, you are
subject to possible contamination by wild yeasts and bacteria, so if
you do skip using it, make certain that everything that comes in
contact with the wine is sanitized.