My boyfriend and I have a long-standing quandary about the best way to
clean and sanitize our bottles and equipment when we brew beer.  Some
products are marked as cleansers, some as sanitizers, and some as
both.  To make things more complicated, some products claim they do
not need to be rinsed, which leads me to the question...

What is the chemistry behind sodium sulfite and antimicrobial agents
like it that allow it to be safely ingested in small quantities yet
still be potent enough to be an effective sanitizer?  The ideas seem
incompatible.  We're not concerned about the cleansing properties,
just the chemistry behind the sanitation.

One of the products we're considering is LD Carlson's One Step
Cleanser (active ingredient: sodium sulfite).  We currently use bleach
but would prefer this is if we could be convinced it worked as
advertised because it is less corrosive and would make bottling the
beer much less work. B-T-F Iodophor (active ingredient: iodine) is
something we're considering if we decided the One Step is simply
ineffective. Here are some relevant links:

http://www.bodensatz.com/staticpages/index.php?page=sanitation
http://ldcarlson.com/public%20catalog/p_61-64.htm

There are several explanations, some explanations involving
interference with proteins that a cell needs to survive and grow and
one explanation involving chemically reacting with the cell's DNA.

Chemically, sulfite is a reducing agent and can react with several
different molecules and ions.

The yeast used in making wine is somewhat resistant to the action of
sulfite since it apparently keeps pumping out sulfite when sulfite
enters the yeast cell. With sulfite around, the yeast survives and
functions, but bacteria that cause unwanted changes are inhibited or
killed.

(Oxygen is excluded in making beer and wine; in the presence of
oxygen, cells can probably oxidize sulfite to the more inert sulfate,
but I didn't look that up specifically. This may explain why we can
tolerate some sulfite in wine; commercial beer apparently no longer
contains sulfite.)

Some people, more so if they are asthmatic, are sensitive to sulfites.

This scientific article lists current suggestions on how sulfites work

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=525195

"Postulated mechanisms of sulfite toxicity or inhibition of microbial
growth include reactions with protein disulfide groups (3, 19, 25),
inhibition of enzyme activities by inactivating their cofactors (e.g.,
thiamine pyrophosphate) (31) or coenzymes (e.g., NAD) (20, 25, 27,
29), and rapid depletion of ATP and ADP pools (14). Sulfites may also
react with pyrimidine residues of nucleic acids (17, 26), which can
lead to genetic damage and cell death."

The disulfide groups connect parts of a protein together and help
proteins hold their shape so they can function; sulfite probably
reduces the disulfide group, breaking it into two unconnected
sulfhydryl groups. The cofactor and coenzyme mentioned are additional
molecules (derived from vitamins in the above cases) that are needed
for certain enzymes to work.

The following article indicates that the strain of yeast used in
winemaking pumps sulfite out of its cells; the yeast used in making
beer may be able to do the same thing.

http://www.cgrb.orst.edu/faculty/bakalinsky/

"Our results suggest that sulfite resistance in S. cerevisiae is due
to the presence of a protein called Ssu1 that acts as a ?sulfite
pump?, keeping levels in tolerant cells low enough to prevent
toxicity."

"S. cerevisiae" is the species name for yeast used in making wine and beer.

If you are interested in what the FDA says about sulfite sensitivity
in peoply, you could go here:

http://www.fda.gov/fdac/features/096_sulf.html