HOMEBREW Digest #5330 Wed 07 May 2008

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  RE:  Braggots ("David Houseman")
  Re: Peer review of Aeration Methods (Fred L Johnson)
  Video from Big Brew Day ("Lemcke Keith")

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---------------------------------------------------------------------- Date: Wed, 07 May 2008 07:37:05 -0400 From: "David Houseman" <david.houseman at verizon.net> Subject: RE: Braggots Dick, Not to be pedantic but there are a number of reasons to boil wort for longer than 30 minutes other than to extract bitterness from hops. Especially in the production of Scotch ales where the extended boils (2 hours) create the caramel and smokiness characteristic of Scotch ales. You might get away using extract rather than all-grain and boiling a gallon of wort down to a pint to create the caramelization. Suggest reading the style book on Scotch Ale before you head off on this venture. Dave Houseman Return to table of contents
Date: Wed, 7 May 2008 07:55:26 -0400 From: Fred L Johnson <FLJohnson52 at nc.rr.com> Subject: Re: Peer review of Aeration Methods Chan Lay posted a number of useful comments and questions to the Aeration Methods paper, which I would like to address below. (Thanks, Chan.) > > > I'd be interested to know what your O2 level was (in ppm) for the > rocking shaking method after 15min, as the general concensus is that > 8ppm of dissolved oxygen is usually all one can expect to acheive from > either shaking/rocking or from using an aquarium pump with an air > stone. Oxygen saturation levels on the days and at the temperatures and at the location on which these experiments were performed ranged from 8.04 mg/L to 8.36 mg/L. You can simply multiply the % saturation value by these numbers to get an idea of the absolute levels of dissolved oxygen in the experiments. You will achieve different absolute levels depending upon the atmospheric pressure and temperature at which you perform the aeration. > > Just some critical review that may/may not help with future studies > when expenses allow: > > 1. You've highlighted water was used instead of wort due to expense. > Using wort instead of water would be the first thing i'd change. (As > you already know, there are different O2 saturation levels between > wort and water) I agree that the better experiment would have been performed in wort, but I seriously doubt any significantly different conclusions would have been made. In fact the graph may not have changed at all except for the % saturation value at the start. The absolute solubility of oxygen in wort is, as stated, somewhat lower than in water and will undoubtedly depend upon the solute content (gravity) of the wort, but I doubt that the rate of dissolution is very different than for water. > > 2. Repeat the experiment at least 3 times (incorporate error bars > to fig1) I agree. The absence of a measure of repeatability is the greatest weakness of the reported results. I was actually too lazy to repeat these because I seriously doubt the conclusions would change and the exact values are not important anyway (in my opinion). > > 3. Continue measuring the dissolved O2 level once you've ceased > aeration to monitor if O2 levels continue to increase/decrease. The dissolved oxygen content would undoubtedly continue to increase until saturation is achieved, but the rate at which the oxygen dissolves would be lower than the rate achieved by actively aerating. > > 4. As a -Ve control, measure the dissolved O2 level of a carboy > fermenter filled with water/wort (filled from the bottom with out > splashing). This can be your baseline. Be interesting to see if there > is a increase in O2 level from just the surface contact with air. The experiment using the bucket was performed with minimal splashing, just as you suggested. DO was measured immediately after the 5 gallons had been transferred to the bucket, so there was not a significant amount of additional time for oxygen to dissolve into the water after the transfer was completed until it was measured. I doubt using a carboy would make a significant difference. The bucket experiment does illustrate that a significant amount of oxygen is dissolved in the water by even a gentle transfer. As I said, there may be sources of oxygen entering the water other than when it leaves the tubing and enters the fermentor. > > 5. As a +Ve control, measure the dissolved O2 level of a full carboy > that has been excessively oxygenated with pure O2 via airstone. This > can be your saturation point. The purpose of the experiment was not to re-determine the solubility of oxygen in water/wort, and the values in the experiment were expressed with regard to the well known published values of oxygen solubility in water. Using pure oxygen would undoubtedly dissolve more oxygen in the water or wort, as I acknowledged in the paper, and future experiments to determine the absolute levels of oxygen in water/wort versus time would be useful, as they could provide guidance to the homebrewer of how long he should pump oxygen into his wort to achieve the level desired. I think the bigger and more difficult question to answer is, "What is the desired level?" > > 6. Do a yeast count and pitch homebrew levels of yeast (eg 1 mil > cells/ML/plato) and then measure the opitcal density (600nm), to > determine the affect each aeration method has on yeast division. Such experiments are actually pretty well published. Providing a continuous supply of air to the yeast allows for essentially maximum growth, but it has undesirable affects on flavor. Hence, methods of aeration for maximum yeast growth are not good methods for making tasty beer. As you probably know, some brewers would like to avoid aerating the wort entirely, as undesirable oxidation products can be produced by wort aeration prior to fermentation. You may be hinting at the bigger question I mentioned above, i.e., to determine how much oxygen is best for making beer if only a single aeration/oxygenation is performed. That is no small undertaking. (Incidentally, one should always remember that air/oxygen is in the headspace of the fermentor after the aeration is finished, and this headspace continues to be a source of oxygen for the yeast until they finally consume it or blow it off. Fred L Johnson Apex, North Carolina, USA Return to table of contents
Date: Wed, 7 May 2008 10:54:32 -0400 From: "Lemcke Keith" <klemcke at siebelinstitute.com> Subject: Video from Big Brew Day For those HBD members looking to plan for next year's AHA Big Brew Day, the event held here in Chicago at the home of Randy Mosher & Nancy Klein shows how to "do it up right"! Despite cool weather, the amazing food & beer propelled brewers & beer lovers through a terrific day. You can see the video highlights on YouTube at http://www.youtube.com/watch?v=-uscDiuthHA , and check out the other Big Brew Day videos while you are there. Thanks, Nancy & Randy!!! Keith Lemcke Return to table of contents
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