On 29 Dec, 18:39, DogMa > wrote:
> Interesting - while not any kind of microbiologist, it's my impression
> from a couple of dozen food/drink projects (plus random reading) that
> pathogenic bacteria and fungi are not usually killed by freezing.
> Rather, their metabolism and reproduction are suspended for the
> duration. Is there evidence that the living elements in Pu-erh that (are
> alleged to) cause beneficial aging could be harmed by freezing?

I understand that the balance of kill versus suspended animation is
related to speed of freezing - a slow freeze being the most lethal -
quick freezing with intimate contact (liquid N) being non lethal. I
don't believe anyone has tested the effect of freezing on susbsequest
maturation of pu erh but would not want to risk mine to the the
uncontrolled and spatially variable cooling of a domestic freezer.

> > Carbon *dioxide ... requires the tea to be
> > infused with the gas in an hermeticly sealed vessel (taping up a
> > closet would not contain it or would need an excess of CO2 - which
> > also kills higher life).
>
> Perhaps you could amplify here, Nigel. My empirical observation is that
> this worked fine both times I tried it, without even bothering with tape
> - I only mentioned that in case someone has a very loose-fitting closet
> or cabinet door. The evaporating lumps of dry ice quickly fill whatever
> space is needed, then continue to emit CO2 until they have sublimated
> completely. Even then, I suspect that lethal concentration for bugs
> isn't that much higher than the 10% or so that's fatal to larger
> life-forms. Leaks and breezes in the average home would probably leave a
> normal closet or cabinet at that level for a few days, once it was fully
> "charged" with CO2.

Dunno. I have used it thus in what we in UK call a picnic box - an
insulated plastic box with a snap shut lid - this gave a virtually
100% CO2 atmosphere. English closets, at least, are pretty leaky
things. CO2 is heavier than air and will tend naturally to drain out
of a closet (like propane gas would, or diethyl ether). Our closets
would need more than the doors taping to hold in a heavy gas for
several days.
.
> I passed along the comment as cited by senior engineers (not scientists)
> at what I think was then Europe's largest coffee company ... Perhaps
> their point was that absent a valve, the (two-way) leak required to
> avoid bag explosion would allow in too much oxygen.

Yes, that was the problem with the then used pin hole valve, once the
positive CO2 pressure reduced then oxygen diffused in.

Nigel at Teacraft