On Sun, 25 Oct 2009 09:26:52 -0400, blake murphy
> wrote:

>On Sun, 25 Oct 2009 09:03:29 -0000, john royce wrote:
[snipped]

>have you done this many times? the difference could be in the garlic:
>
> The discoloration is due to pigments that form between sulfur compounds in
>garlic and amino acids. When the garlic tissue is disrupted, as happens in
>processing, an enzyme is liberated and reacts with it to form
>thiosulfinates compounds that then react with the natural amino acids in
>the garlic to form blue pigments. The age of garlic determines how much
>isoalliin there is in the first place, and the nature of the processing
>determines how much enzyme is liberated.
>
>Original thoughts and ideas:
>
>Garlic is known to contain sulfur compounds which can react with minute
>traces of copper to form copper sulfate, a blue or blue-green compound. The
>amount of copper needed for this reaction is very small and is frequently
>found in normal water supplies. Raw garlic contains an enzyme that if not
>inactivated by heating reacts with sulfur (in the garlic) and copper (from
>water or utensils) to form blue copper sulfate. The garlic is still safe to
>eat.

{more snipped}

This is indeed a difficult question, as the number of variables is
great. FE: What Blake says is correct. It follows that the two
vinegars may be been manufactured in different vessels, and
you have no control over that. Also, natural vinegar is made
in wood or crockery, from (wait for it....) RICE! Some can
be made by a bulk process using a mash or concentrate
that *contains* rice, along with other stuff. An innocuous
example is OJ (made from concentrate in a factory). Some
soy sauces do NOT use soybeans as a starting material.
FOr that reason, there are lawsuits in existence to force
labelling of "Soy Sauces" made from anything other
than natural soybeans in their natural state.

I use Marukan or other Japanese vinegars exclusively when
I need rice vinegar. If I'm out I use cane vinegar from the
Philippine Islands, either the Sarap brand or White Swan,
which I suspect are made at the same facility.

I do NOT feel comfortable with most CHinese products
unknown to me, although I've had good luck (I ain't dead
yet) with ShaoTsing (AKA TsingChao) cooking wine.

For all you know, one of your vinegars may have been made
in copper vessels, with lead or tin solder, rather than in food
grade S/S.

Good luck

Alex