Hi Stewart, I apologize in advance for the somewhat anecdotal nature of my experience with this and will try to avoid to much hearsay. But I have been using sterile air to aerate my wort since I started my brewery 3 years ago, so I've got some rough level of experience with it.
I have a 10 bbl brewhouse and make both 10 and 20 bbl batches of wort. For a 10 bbl batch I generally pump wort through the chiller(Knockout) at 10gpm while running sterile air through a sintered stone at 12-15LPM depending on the batch. I have to confess I haven't recently measured the DO I'm achieving in wort with my DO probe, but early on in the life of the brewery I found that about 8ppm was about the most I could achieve, I may have seen 9ppm at one point, but increasing air flow rate past a certain point did not increase the DO in wort. I don't have charts handy, but I believe most literature will tell you that about 8ppm is the max you can achieve using air at 68dF. I would imagine you could achieve slightly higher at 50dF if you were say knocking out a Lager, but I have no data to show the difference, and I imagine it is small. Additionally, on a 20 bbl 'double' batch, I will knockout as fast as possible, which is approximately 14 gpm for me and aerate at 15LPM.
If you are interested in spending some money to be able to measure what you are achieving I would highly recommend this meter, which is for pH primarily, but a DO probe can be plugged into it. It is only for ppm level DO, so wort measurements. It is not capable of ppb level measurements so won't be useful for checking DO in beer.
Multiparameter edge pH Meter - HI2020-01 | Hanna Instrumentsedge® Compatible Digital DO/Temperature Electrode - HI764080 (hannainst.com)If you don't already have a pH meter I would recommend this with the knowledge that it can also double as a DO meter. But that may be more than you want to spend.
While 8ppm may not sound like a very high number for wort aeration, I find with the American Ale yeast strain I use it is completely adequate. I have also had plenty of successful lager fermentations. One thing you could try if you wanted more aeration for say a higher gravity wort is to bubble in additional air in the fermentor 12-24 hours into fermentation. I know that may be anathema to many brewers, but there seems to be strong evidence that aeration at that stage is a strong driver of fermentation and yeast growth. Oxidation worries should be minimal at that stage, as the yeast will rapidly consume all oxygen provided.
The main thing I would say about using air as opposed to oxygen is that you aren't really able to over oxygenate the wort, it just isn't possible in my experience, so better to really drive in as much air as you can to make sure you are achieving maximum DO. The one annoying thing I come across when really giving it the full beans on aeration is excessive foaming of wort in the fermentor while filling. I don't think this is much of a problem other than a nuisance to clean up, but some people may be worried about long term effects of foaming the wort on head retention. I haven't noticed a problem, but it could be something someone may want to consider.
Again, sorry for all the hearsay and lack of hard evidence to back up my claims, but this is my experience with using sterile air and I hope it helps.
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John Kochendorfer
Head Brewer
District Brewing Company
Mount Vernon WA
(425) 275-3447
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Original Message:
Sent: 01-27-2023 14:07
From: Stewart Brown
Subject: Wort aeration with air and flowrates
Hello Brewers,
I am getting a rotometer for our aeration line, so far we have just been setting the flowrate based on visual in the sight glass.
I was wondering if anyone out there has some DO in wort data and flowrates using sterile air. I know there are several variables that affect the solubility of O2 into wort (gravity, temp, Fermenter size), just looking to get a baseline flowrate to start as I do not have access to a DO meter. Any data and experience you can share is much appreciated.
Just for some additional info. We have 20bbl fermenters and most beers are of average strength 12-14p
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Stewart Brown
Director of Brewing Operations
Banff Hospitality Collective
Banff, Alberta
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