From the HBD Archive
From: BOB JONES <>
Subject: Air filters
Date: 1992-06-19 21:10:00 GMT

Let me tell you about an experiment I read about in a microbiology text
once upon a time. Keep in mind here that I am not a microbiologist. There
was this test apparatus set up to try and figure out why things would spoil.
You see in those days they didn't know about yeast or bacteria and didn't
have high power microscopes. They didn't even have HLP :-). Ok the test
setup looked something like this...

=====[ cotton plug]=====< air pump
|| ||
| || || |
| || || |
| |
flask | |
| |
| |
| growth |
| media |


Ok, now you boil the growth media in the flask for a while, then you turn
on the air pump and push air through the cotton filter onto the growth
media. Well nothing would grow in the media. If the cotton plug was removed
and the experiment repeated, the media would quickly cloud up with something
growing in it. This told the experimenters that the spoilage mechanism must
be air born. Well we all know that, but what I learned was how good a
bacterial filter a cotton plug is. So for all you brewers out there looking
for .2 micron filters, you already have one in your medicine cabinet. Do what
I do and just poke a piece in the hose. I am told you should use real cotton
and not polyester. Maybe in a future post and can describe my gadget for oxygen
injection that doesn't require an aquarium pump.

Bob Jones

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