From the HBD Archive
From: lbr@gatech.edu
Subject: Wort Aerating
Date: 1989-02-08 18:36:56 GMT

jhersh@rdrc.rip.edu writes:

> I don't think 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.

Second part is certainly true. Homebrewers too often pitch a packet of
dry yeast (yuck!) and wait for it to build up in the wort. Pros pitch
thick slurry or actively fermenting starter. The pros may aerate less,
but I think they do aerate some (with sterile filtered air, of course).

> 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.

> 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....

Have you read Noonan's book "Brewing Lager Beer"? It is by far the most
technical homebrew book I've seen, though of course it doesn't compare
with professional brewing literature. He indicates that some of the
products you mention, such as fusel alcohol, come from *inadequate*
aeration for the wort, and that aerobic fermentation must occur before
the anaerobic fermentation starts. Anaerobic fermentation then takes
place at a lower temperature after some of the yeast nutrients have been
depleted. He recommends high pitching rates, well in excess of what most
beginning homebrewers use, so I don't think that having enough yeast
obviates the need for oxygen.

I don't think you're right that adding a lot of yeast to oxygen-poor
wort is a good way to start fermentation, but I'm no expert. Please
send me some paper references if you get the chance. I get down
to Georgia Tech's library sometimes and they should carry major
technical journals.

Many homebrewers introduce too much oxygen after primary fermentation,
especially during racking and bottling. This is bad. But everything
I've ever read says that the yeast need oxygen when the fermentation
starts.

Postscript: Georgia Tech rejected e-mail I tried to send to rdrc.rip.edu

Len Reed
gatech!holos0!lbr

Back New Search

The posts that comprise the Homebrew Digest Searchable Archive remain the property of their authors.
This search system is copyright © 2008 Scott Alfter; all rights reserved.