---

	FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
		Digest Janitor: pbabcock at hbd.org


***************************************************************
        TODAY'S HOME BREW DIGEST BROUGHT TO YOU BY: 

                 Sponsor The Home Brew Digest!
     Visit http://www.hbd.org/sponsorhbd.shtml to learn how
			 
    Support those who support you! Visit our sponsor's site!
********** Also visit http://hbd.org/hbdsponsors.html *********

DONATE to the Home Brew Digest. Home Brew Digest, Inc. is a 
501(c)3 not-for-profit organization under IRS rules (see the
FAQ at http://hbd.org for details of this status). Donations
can be made by check to Home Brew Digest mailed to:

HBD Server Fund
PO Box 871309
Canton Township, MI 48187-6309

or by paypal to address serverfund@hbd.org. DONATIONS of $250 
or more will be provided with receipts. SPONSORSHIPS of any 
amount are considered paid advertisement, and may be deductible
under IRS rules as a business expense. Please consult with your 
tax professional, then see http://hbd.org for available 
sponsorship opportunities.
***************************************************************


Contents:
  O2 diffusion (mabrooks)
  Re: stir plate oxygen limit (Fred L Johnson)


* * * * * * * * * * * * * * * * * * * * * * * * * * * * *
*           The HBD Logo Store is now open!             *
*            http://www.hbd.org/store.html              *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * *
*   Beer is our obsession and we're late for therapy!   *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * *

NOTE: With the economy as it is, the HBD is struggling to 
meet its meager operating expenses of approximately $3400
per year. If less than half of those currently directly
subscribed to the HBD sent in a mere $5.00, the HBD would
be able to easily meet its annual expenses, with room to 
spare for next year. Please consider it.

As always, donors and donations are publicly acknowledged
and accounted for on the HBD web page. THank you

 
Send articles for __publication_only__ to post@hbd.org

If your e-mail account is being deleted, please unsubscribe first!!

To SUBSCRIBE or UNSUBSCRIBE send an e-mail message with the word
  "subscribe" or "unsubscribe" to request@hbd.org FROM THE E-MAIL
  ACCOUNT YOU WISH TO HAVE SUBSCRIBED OR UNSUBSCRIBED!!!**
IF YOU HAVE SPAM-PROOFED your e-mail address, you cannot subscribe to
  the digest as we cannot reach you. We will not correct your address
  for the automation - that's your job.

HAVING TROUBLE posting, subscribing or unsusubscribing? See the HBD FAQ at
http://hbd.org.

LOOKING TO BUY OR SELL USED EQUIPMENT? Please do not post about it here. Go
instead to http://homebrewfleamarket.com and post a free ad there.

The HBD is a copyrighted document. The compilation is copyright 
  HBD.ORG. Individual postings are copyright by their authors. ASK 
  before reproducing and you'll rarely have trouble. Digest content 
  cannot be reproduced by any means for sale or profit.

More information is available by sending the word "info" to 
req@hbd.org or read the HBD FAQ at http://hbd.org.

JANITORs on duty: Pat Babcock (pbabcock at hbd dot org), Jason Henning,
                  and Spencer Thomas



----------------------------------------------------------------------


Date: Mon, 23 Mar 2009 09:31:52 -0400
From: mabrooks at vt.edu
Subject: O2 diffusion


When it comes to "oxygenation" of most liquids, there are numerous way to go
about it.  The simplest way to get to O2 saturation level in a room temperature
yeast starter, assuming you have a stir plate and proper size container (large
surface/vol area) and proper size stir bar, is to simply cover the flask
loosely with foil and turn on the stir plate.  The O2 transfer from air will
work wonderfully and you can assume saturation levels will be maintained fairly
well.  Diffusion and transfer laws will provide all the exchange needed for this
task. I really cant see the need to go through the trouble of putting in an air
diffuser stone and using a stir plate unless for some reason the yeast O2 demand
was
really excessive? or if the container was "sealed" tight, which I don't see the
need for? If the starter is at fermentation temps the issue is even
less of a concern as O2 has a higher sat level at lower temps.

Typical situations which would necessitate the use of a diffuser stone, is if
you have a
very large yeast starter (> 3 gallons) and the surface area (volume exposed to
air) is very small and the yeast O2 demand is very high (very thick yeast
starter). Typically one would
use pure O2 for this type application.  Otherwise, the natural transfer of
O2 from air into a dilute wort/yeast starter (or other liquid) being stirred is
very
efficient, especially below 60 degrees F.  Its all about the "demand" for O2 in
the starter, and for starters of less then 2 quarts or so, you don't need to
use a diffusion stone, especially if you have a stir plate.


Matt B.
Northern VA.

BTW: I have an extra stir plate I bought and didn't use (still new) if anyone is
interested I would be willing to sell.  Stir bars are included.



Date: Sat, 21 Mar 2009 10:09:43 -0500
From: "Devonna Dieterle" <djdieterle at hughes.net>
Subject: Subject: Re: stir plate oxygen limit



Matt stated he didn't want to pump filtered air directly into the starter do
to the infection risk. Fred stated he pumps air into the starter headspace.
With a good quality inline air filter which is rated to filter to .023
micron is infection a risk and which way is more effective, pump into the
liquid or the headspace(if there is a difference in oxygen absorption)
I ask because I pump air directly into the liquid using 2 filters in series
through a stainless bubbler wand on a stir plate, with the starter vessel
sealed from the outside air and generally follow Mr. Maltys starter volume
calculator for quantities of 1.040 canned wort for stepping up.

Jeff Dieterle



Return to table of contents


Date: Mon, 23 Mar 2009 22:19:17 -0400
From: Fred L Johnson <FLJohnson52 at nc.rr.com>
Subject: Re: stir plate oxygen limit

Jeff asks if pumping air directly into the wort is more effective or  
less effective than pumping into the head space of a stirring  
starter. Undoubtedly, pumping air into the wort directly is more  
effective at dissolving oxygen in the wort than pumping into the head  
space, but it probably isn't much more effective if the air supply is  
continuous and the starter is stirred. One only needs to dissolve  
oxygen in at the rate it is used by the growing culture. When the  
yeast are at their peak rate of daughter cell production, one might  
see a benefit of pumping directly into the medium, but I have no data  
to support this. Pumping air directly into the wort leads to lots of  
foam, so one would have to turn down the air flow rate and/or add an  
agent to break the surface tension to minimize foaming--something I  
prefer to avoid.

Fred L Johnson
Apex, North Carolina, USA



Return to table of contents

---