--- In Distillers@yahoogroups.com
, "Bob Bourne" <bourne@v...> wrote:
> 33C and Harry's "mercaptans"?
> "The optimum temperature for fermentation if one is thinking of
> than flavour is about 33oC."
> From John Stone's Making Gin & Vodka.
> The idea seems to be (using baker's yeast here) the nasties are
> on distillation. I'm talking about making vodka only here. Are the
> mercaptans left behind on distillation?
> Comments appreciated.
There's not a great deal of info around re mercaptans and
distilling. However it's well documented in the wine industry, and
wash is essentially a wine. I got hold of a couple of things worth
The second possible cause is hydrogen disulfide or mercaptans. There
are numerous potential pathways for these stinky compounds to get
into your wine. Sulfur spraying in the vineyard too close to the
harvest date is one possibility.
Yeast spit out elemental sulfur in the form of hydrogen sulfide.
Other causes might include insufficient nitrogen levels during
fermentation, high fermentation temperatures, low fermentation
temperatures, a too-rapid fermentation or anything that will stress
your yeast out.
Most often, hydrogen sulfide smells like rotten eggs and mercaptan
smells kind of oniony, but I've seen them develop into burnt rubber
aromas in finished wines.
Sometimes hydrogen sulfide and especially mercaptans can't be
removed at all and even professional folks have to live with the
stinky results of naughty yeast. Never fun, but a reality of the
And from the Homebrew Digest, an extremely good article on yeasts,
like EC-1118, this extract...
Except for a few mutated yeast, H2S is a natural metabolic pathway
in the production of two of the sulfur containing amino acids. The
big problem is to minimize the excess production of H2S. An
adequate supply of nitrogen (DAP and autolyzed yeast) throughout the
first half of the fermentation goes a long ways to achieve this. An
unhealthy yeast cell will die prematurely and cause the production
of mercaptans (sulfury type compounds)
at the end of the fermentation.
So if you want your wash smelling like rotten eggs, or onions, then
go ahead and ferment hard and hot, or stress your yeast with under-
As to whether it carries over in distillation, well I don't rightly
know. I have this info from the online encyclopedia...
They are colorless liquids, which are insoluble in water and possess
a characteristic offensive smell. On oxidation by nitric acid they
yield sulphonic acids. They combine with aldehydes and ketones, with
elimination of water and formation of mer-captals and mercaptols.
Ethyl mercaptan, CjHs.SH, is a colorless liquid which boils at 36.2
C. It is used commercially in the preparation of sulphonal.
The mercury salt, Hg(SC2H6)2, crystallizes from alcohol in plates.
When heated with alcohol to 190 C. it decomposes into mercury and
From that info I assume that while it has a low boiling point and
MAY be driven off early in distilling, it also is capable of
combining with ahdehydes and ketones, both of which are present in
malt whisky. That makes me think that it probably will carry over.
I've never noticed any rotten egg or onion smells from any of my