It's nice to see the numbers summarized--thanks for posting this. When do these dissolved oxygen levels translate into measurable sensory perception on the homebrew scale? I of course accept cold side aeration as a concern (and have experienced it myself)...I just wonder about the tempo of appearance of detectable effects under homebrewery conditions.
Outlining two scenarios typical for my beer...
- I have a batch that is uncarbonated and in the fermenter, and want to serve it at a party within the next day or two. If I quick-carb (either cranking pressure and letting it sit, or crank and shake) using my typical beverage grade gas, when do things start to go south in a detectable fashion? Is it even a worry if I'm serving in a day or two and keeping it cold during this whole stretch?
- I have a batch that is uncarbonated, which I force carb (~1 week), and serve. In my house, stuff typically is on tap for 4-6 weeks before the keg is finished. Again, I'm keeping it cold (≤40F) during this whole stretch.
Relative to the term "accelerated staling," what is the practical sensory time frame for this, if the beer is kept cold? Are we talking 1 day? 1 week? 1 month?
Finally, for the additional 39.94 liters of CO2 described in the article (which tips the calculated dissolved oxygen over the 150 ppb mark), is that over the lifetime of serving the keg? I.e., you're not dumping that full 39.94 liters in on the first day...or second day...or even second week, necessarily. My sense is that the 156.6 ppb mark would be hit only at the very end of the serving cycle. Or am I misunderstanding that section of the article?
I should emphasize again that I'm _not_ disputing the effects of cold side aeration--I'm just wondering about how quickly they manifest at homebrew scales under homebrew handling conditions in a way that the typical taster can perceive them.
I want to kind of take what you’ve said and parse it so we can hit everything you asked/commented on.
First, let’s be clear that we assumed 99.9% purity CO2. Let’s be honest with ourselves and say that of the people who keg thier homebrew, only a small minority of those people are going to be paying attention to/seeking out the purity spec of their gas. In fact, I think it’s safe to assume most people just use the 99.5% Industrial Grade they can locally source and refill. That means that as soon as you’ve carbed your beer to a modest level like 2.5 volumes, you are at 177 ppb, without serving, assuming a sufficient purge, closed transfers, etc. That puts you at the tipping point before you’ve even drank the beer.
So, we wanted to steer clear of any traditional/Low Oxygen debate here because it’s really not about that. I will say however, that while this should be a concern for ALL brewers, it’s a fundamental concern for us because the flavor impacts present themselves in short order. We are talking a few days to a week, at serving temperatures, after hitting 150 ppb that we are losing the fresh malt flavors, hop presence/flavor, etc., in Low Oxygen beers.
We have also had many of the people who transitioned from traditional methods to LO methods comment on how, from a flavor standpoint, they were now able to pinpoint certain flavor degradations across the life of a keg from their old processes. How long does this all take for the traditional homebrewer? It’s hard to say. We have a certain flavor profile distinctive to LO brewing that tells our taste buds when we’ve reached the tipping point. I would be on the lookout for the flavors described by Fix as “Stage B” oxidation flavors in PoBS, but also a diminishment of hop flavors, etc. obviously you want to make sure you are sufficiently purging your kegs, performing closed transfers, keeping the beer cold, etc.
As far as the serving pressure add to the sum total, you are correct. It’s not all added up front, but again, we made some assumptions here:
1.) You are sufficiently purging your kegs. That means liquid purging the ENTIRE keg, including the entirely of the headspace (liquid coming out of the PRV). If you aren’t doing that, you are adding to the DO in the finished beer.
2.) We assumed 2.5 volumes of carbonation. Obviously anything higher increases the DO in the finished beer.
3.) Again, we assume a grade of CO2 that is of a much higher purity than most are probably using.
Ultimately we just wanted to bring to light something that may not have been on people’s radar.
Topic: CO2 Purity and Why It's So Important (Read 18777 times)
