Somewhere on teh intarwebs graham wrote:
> "Barry Harmon" > wrote in message
> . 15.254...
>> Kenneth > wrote in
>> :
>>
>> If you discover an old sourdough in the
>> back of your refrigerator and want to nurse it back to health, stir
>> any liquid that has accumulated on top back into the dough and
>> transfer it to a
>> clean containte.
>
> I've seen this instruction in various places and it has never made
> sense to me. There is probably alcohol in that liquid and I would
> have thought that pouring off that fermentation product and replacing
> it with fresh water would result in a more rapid revival.

"Pouring it off"? I'd be mixing it with coke and a couple cubes of ice. <g>

Seriously though, from my time as a winemaker; Yeast converts sugars to
alcohol at a rate of 1.8:1 (if you have 18% sugar in solution you'll end up
with 10% ethanol when it is fermented dry, all being well). Wine yeast isn't
really inhibited by the ethanol levels until it starts to reach over 13% but
will go higher (The highest naturally fermented ethanol level I've achieved
is 15.5%). 'General purpose" yeast is slowed at a bit lower concentration,
around 10%. (Note "slowed", if the fermentation is allowed to continue long
enough the yeast actually evolves, the less ethanol-tolerant beasties dying
off and the more ethanol-tolerant take their place.)

"Fortified wines" such as Sherry and Port have ethanol added to a minimum of
18% v/v. This is the level at which yeast can no longer survive (same goes
for bacteria and fungi). Which is why you can drink a bottle of port at your
leisure, say within weeks to a month (still got oxidation to worry about)
after opening rather than within days for wine.

Upshot of all my rambling? I seriously doubt that the liquid sitting on the
sourdough starter would be worth opening a bottle of Coke for, and not
likely to inhibit or stop the growth of the micro-organisms (which might
well have become alcohol tolerant if there was enough yeast-food and enough
time [fermentations are very slow at fridge temps] to produce significant
amounts of ethanol anyway.)
--
Cheers,
Shaun.

"Give a man a fire and he's warm for the day. But set fire to him and he's
warm for the rest of his life." Terry Pratchet, 'Jingo'.