From the HBD Archive
From: jhersh@rdrc.rpi.edu (Jay Hersh)
Subject: filtering
Date: 1989-02-03 16:13:43 GMT

Someone said something about not being able to naturally condition your beer
if you filter. Nonsense. For commercial brewers who filter they naturally
condition their beer first, then filter on the way into the bottle or keg.
This allows them to "cold filter" the cold conditioned beer. After all the
filter won't remove the CO2 which is dissolved into the beer. I don't
know how common it is to do this but it is done.

Did someone recently ask a question regarding esters in hops???
Do hops have esters??? It was my belief that esters are the chemical
substances responsible for fruit flavors and aromas. These are certainly
present in flowers of fruit plants, but are they also present in hops??
I had believed that any esters in beer were derived via yeast metabolism.

Mike Fertsch had recently asked about Big Brewer Blowoff and I'm not sure if
my theory as to how they handle this ever got onto the digest so here it goes
again.

1) Think about the ratio of krauesen to wort volume. For big brewers,
depending upon the type of fermenting vessel and yeast (conical has less
ooops vertical cylindrical has less surface area than sideways cylindrical,
lager yeast produces less foam up than ale yeast)
the quantity of krausen to beer volume will be different than for homebrewers.

2) Big brewers add a much larger quantity of yeast per volume of beer
(what I refer to as a critical quantity) than do homebrewers. Homebrewers
rely upon the aerobic fermentation cycle which produces much more energy
for the yeast since it uses a different chemical process to acheive
feremntation. This extra energy is plowed back into reproduction.
I believe it is this different fermentation pathway that is responsible for
the different blowoff by products. I don't thin k that commercial
brewers aerate their wort to the extent that homebrewers do or rely upon
the wort to serve as a media for yeast reproduction to the extent that
homebrewers do.
Anaerobic fermentation is a different process and will also result in yeast
reproduction but to a lesser degree. I believe that the different fermentation
pathway yields fewer of the nasty alcohol by products that aerobic
fermentation generates.

As a last note I also believe that many of these by products are only partial
fermentation products and as such can still be metabolised later on to
be converted from "higher" alcohols to ethyl alcohol in order to release
energy.

Much of this information has been garnered from collections of papers by
European breweries such as BASS and Carlsberg which are present here in
our library. Many of these papers are intended for microbiologists and
since my biology and chemistry background is limited, I only derived
limited knowledge. I would suggest a visit to your local college library
to check various books on yeast. This is a move for the ambitious as much
of what you find may be way over your head, but as they say you can't
learn to swim in a puddle. I will attempt to relocate the books that I
had previously read in order to provide a bibliography. It may take me some
time to get to this since the world has beaten a path to my door lately
and I have yet to finish the better mousetrap.

- jay h
yeast make great pets. I keep them in a five gallon carbouy shaped aquarium
and all I have to do is feed them some malt extract from time to time.

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