Just finished brewing today and have an interesting observation to share/discuss.
Brewed an Imperial Stout OG 1.094. I use an in-line oxygen system into a 7.5 gallon glass carboy with a Hach luminescent dissolved oxygen meter in the carboy. Wort is at 65 degrees. I use the standard 1ppm/degree Plato oxygen per the “Handbook of Brewing”, Priest and Stewart. I have been running this identical oxygen set up for about 2 years now. I run the wort into the carboy and adjusted the oxygen flow to hit my desired number, then immediately pull the Hach LDO out of the carboy. Today for the first time I decided to leave the LDO in the carboy and take a few readings over the next couple hours. Initial reading upon filling the carboy 20+ppm O2. Did not pitch the yeast. Over the next hour the oxygen saturation is down to 5.2! No yeast, carboy sitting at 65 degrees in the refrigerator. I was blown away how quickly the oxygen came out of solution. Pitched the yeast and thirty minutes later oxygen saturation of zero!
Appears to me that my in line oxygen set up is near worthless as most all the oxygen came quickly out of solution in the carboy. I always thought an in line oxygen system was the most efficient method. I now suspect any other delivery system would suffer this same problem. Perhaps a better way is to rack to the carboy and run a very slow, continuous oxygen flow via airstone into the carboy for the first 24 hours?
I had expected that O2 would come out of solution quickly, especially above its saturation point, but it is surprising that it got down to 5ppm so quickly. Still, you’re fermenting beer, not growing yeast… I’d stick to continuous aeration in the starter. Unless you’re fermenting an ultra-high gravity beer, too much oxygen in the wort could have a deleterious effect.
I would not oxygenate after pitching the yeast. How confident are you that the DO meter is accurate for long periods of time?
If the temp is 65 the max O2 is higher than 5.2 for water, but I’m not sure how the presence of sugar affects that. You may be better off corking the carboy when you are done filling it - any O2 that comes out of solution will be sitting in the headspace and be reabsorbed given time, assuming the wort is not at saturation. Once the yeast is pitched and the dissolved O2 is taken up, some of the O2 in the headspace will dissolve into the beer until fermentation is vigorous enough to drive it out of the carboy.
I have heard before that yeast consume all dissolved oxygen within the first half hour. So wouldn’t it simply be most efficient to oxygenate after the yeast has been pitched (and acclimated?)?
Only if you can tightly control how much O2 you are adding. Wort saturated with O2 is fine for pitching yeast, but continually adding O2 as the yeast are taking it up can lead to oxygen toxicity.
What I mean to say is to still apply just one dose of O2 but to do it fairly soon after pitching rather than to oxygenate, lose some O2, and then pitch.
For instance, if I brew a lager, I like to chill and rack off the break material before pitching the next morning. So if I oxygenated the night before pitching, I’d lose much of my O2 by the time I did pitch. If I wait until after I pitch, the yeast take it up immediately. No waste. Right?
If you can control how much you are using then it is no issue. But you could just wait to oxygenate after you rack, right before pitching. It is safer that way, with no risk to the yeast. I typically oxygenate and then pitch immediately, as opposed to pitching and oxygenating immediately.
Am I missing something? A Google search of “oxygen toxicity in yeast” turned up nothing related to brewing. And in the “yeast” book, it says,“Generally you do no want to add oxygen later, as it can disturb the delicate balance of flavor and aroma compound creation.” It also suggests, in high gravity beers, “adding oxygen between 12-18 hours after pitching can make a tremendous difference in attenuating the beer.” But nothing about oxygen toxicity. Doesn’t spinning fermenting wort on a stir plate introduce oxygen continually? Why would 30 seconds of oxygenation be a good thing for the yeast 10 minutes before pitching, but be a bad thing 10 minutes after pitching?
I don’t mean to be a smarty pants but I’m suddenly cornfused about something I thought I understood! ???
If you are adding pure o2 you can super saturate the liquid with o2. particularly right where the o2 is going in. if you are adding o2 from the atmosphere you are never going to achieve anything like the ppm of DO that you can with pure o2. it’s the ppm that makes for a toxic situation.
So adding pure O2 before pitching is good. And adding excessive o2 before pitching will negatively affect the flavor. And aerating after pitching can be ok in certain situations like starters and high gravity beer or mead. But pure o2 after pitching is always bad. Is that right?
I’ve given O2 some consideration, at one point almost ordered a regulator and stone. I currently splash aerate. Once when I drain my boil and again after cold crashing when I put it in the fermentor. I don’t think I will change. Its not been a problem.
You can’t add excessive O2 before pitching, it is not possible due to saturation.
Adding O2 to beer (not wort) negatively affects flavor.
Aerating after pitching in starters is fine because although that can affect the flavor stability in a negative way, you are not drinking your starter.
Pure O2 after pitching is not always bad, as long as it is done in a controlled, measured manner and you don’t add so much that it is toxic to the yeast, and as long as it is done before fermentation has progressed too far (because then it can affect the flavor and stability).
Essentially, oxygen toxicity can be caused by oxygen radicals like superoxide (O2-) that are generated in and can damage the cell. Superoxide is grabbed by superoxide dismutase, which alternately converts it to either hydrogen peroxide (H2O2) or molecular oxygen (O2). Since the H2O2 can also damage the cell it is further degraded to water and oxygen (2 H2O2 → 2 H2O + 2 O2). This is the same reaction that happens during respiration in our bodies all of the time, and dealing with it is important enough that we have superoxide dismutase all over our bodies, circulating and in every cell.
Your google search may not have led to anything that the authors directly relate to brewing, but the yeast strains that are used in labs are derived from beer/bread strains and share nearly all of their genetics with our brewing strains.
I think yeast oxygen toxicity is a wildly propagated urban myth for brewers. No doubt you can kill most anything with excessive oxygen. However, with our brewing practices this is unlikely to happen and needless worry. Excessive oxygen, in my opinion, is rarely a problem.
I do believe you can use excessive oxygen that negatively affects beer flavor, producing fusel alcohols and acetaldehyde.
I do believe that consistent control of dissolved oxygen in wort is critical to steady yeast growth and yeast production of desirable flavor compounds.
Low gravity beers <1.060 are very forgiving of mistakes and this information is not as applicable to these beers. High gravity beers >1.080 are much less forgiving of mistakes and this information is more important for their success.
Pretty sure. I hit it with a very long o2 blast. Never got any growth or action on a very fresh pack of yeast that swelled quickly in Wyeat packet then trasferred to stir plate. Nothing but spinning.
One website requires a login. The other doesn’t really answer any brewing-specific questions.
So too much oxygen kills yeast. But how much is too much? Is there a threshold ppm? Or is it the physical act of pure o2 bubbling thru the yeasty wort?
