oxygen: When to say when?
Thanks to all who answered my filtration questions! Problem solved! Beer to warm on outlet side! Thanks.
I set my oxygen regulator (made by a mediacal company) to 6 LPM. It's enough to produce a steady flow through the wort in the sight glass. Ideally, for my yeast strain, I want to inject 1 liter of oxygen per Bbl.. This being so, according to my "trusty" regulator, I would only need to run the Oxygen for 1 minute+ for my usual 7 Bbl batch. That just doesn't seem right to me, since all of the brewers who came before me would keep the oxygen running for an arbitrary amount of time, at least 2/3 the time it took to knock out. I ws told by one that because it is a medical regulator, it is not necessarily accurate. If this is so, how will I ever know I am using the correct desired amount of oxygen? Your input is greatly appreciated!
This is probably not an option for you, but if you could get clean compressed air, that would be ideal. Then you couldn't over-oxygenate. Using oxygen can be tricky and many brewers over-oxygenate without knowing it. Their yeast are sluggish or there are off flavors, but they attribute this to other things. Although it may not be immediately noticable in fresh beer, oxygen strips your wort of anti-oxidants, which causes a "cardboard" flavor among other things in aged beer. In a brewpub this may not be so critical, but if you bottle and your beer travels it is. The reactivity of the compounds in the wort with oxygen increases dramatically with increasing temperature. That's why oxygenation should be done at a low temperature.
Yeast need about 7 or 8 mg of oxygen per liter for normal beers, so not a whole lot (more for high gravity beers). In order to achieve this, but have it evenly distributed throughout the wort, let it bubble slowly into the wort as it passes to the fermenter or pitching tank. If you have a means of measuring the total amount of oxygen you use for a given batch of wort, then you can figure out how much you put in. Of course, some of it doesn't dissolve in the wort. 20 to 30 mg per liter is toxic for yeast.
Because I didn't have another option, I set the rate just through trial and error by observing flow rates and the pressure guage. If you always have the same wort flow rate then you can set the bubble rate in the sightglass. My yeast always took off really well and never showed signs of over-oxygenation. If you have healthy yeast in the log phase when they're pitched, then you can under-oxygenate a little and not worry. Generally speaking, catering to your yeast's needs helps elminate a lot of problems in the brewery, i.e. take care of the boys and they'll take care of you.
Last edited by crassbrauer; 04-25-2006 at 04:19 PM.
I believe that what you're really interested in here is the amount of oxygen that actually gets dissolved in the wort. This will vary with temperature of knockout, length of hose run between oxygen injection and receiving vessel, turbulence in the line (are you getting turbulent rather than laminar flow? does the line make sharp corners? etc.), surface area contact of oxygen to wort (are you injecting through a scintered stone?) and other factors. Ultimately, there's no way to know (I believe) exactly what's getting dissolved without the use of a DO meter. Of course, too much oxygen at any given time will cause excessive foaming in the fermenter as well. We used a trial and error approach (measuring, mainly, lag time before active fermentation) and came up with 3.5 L / min over the entire course of our 30 minute knockout (70 F for 20 bbl) for standard gravity beers and 4.5 L / min for high gravity beers. This seems to work well for our set-up, but I'm confident that results will depend on the specifics of your set up. Good luck.
The Duck-Rabbit Craft Brewery
I second the above post- lots of variables. We use a small stone on the outlet of the heat x, and a 30' 1 1/2" hose to all of our fermenters regardless of their proximity to the heat x., 2 LPM over a 67F 35 min. cool-in for ~11 Bbls works well here. We brew 2 batches to fill most of our fermenters, but not in one day. The next day (2nd brew) needs no air. I have heard that you CAN over-oxygenate with medical grade O2(which we use), but not with filtered compressed air. I have used both in the past with good results.
Not to get off subject here, BUT....
Originally Posted by pbutlert
I remember reading in one of my brew books not to use medical grade O2 because it can contain compounds that inhibit bacterial growth and can, therefore, be harmful to your yeast.
Just my random thoughts from the margin......
Rule of thumb: Look at your yeast volumes, before and after. Too much yeast = too much O2.
...or too few yeast (or lots of dead ones) = too much O2.
You should pitch around 10 - 20 million cell per ml (depending on whether you're brewing with ale or lager yeast); they should reach around 50 - 60 million. If you overpitch and oxygenate, then you'll have too much yeast.
Oxygen is toxic to living cells in high concentrations. If it weren't for it's essential role as an electron receptor in respiration then you wouldn't want it around, because free radicals damage DNA and, in some cases, cause cancer, hence the need for anti-oxidants in your diet and your beer.
Last edited by crassbrauer; 04-27-2006 at 02:36 AM.