O2 Impurity in Carbon Dioxide: How Much is Too Much?

I recently saw a post on a brewing forum where someone was wondering about air contaminated carbon dioxide and its impact on dissolved oxygen levels in carbonated beer. Air in CO2 really can raise the dO2 levels in your beer, so I thought it would be worth discussion.

Back sometime in the late 1980s (I think) someone passed along to me a table showing the exact amount of dO2 that would be picked up in beer if specific amounts of CO2 were injected into a process pipe or finished beer vessel. I’ve been hoping to find a copy of that article ever since, so maybe someone out there can help steer me to it. But in the meantime, with a tip of the hat to the original author(s), here is a copy of the table:

Co2 Injected O2 Impurity

0.001%

O2 Impurity

0.005%

O2 Impurity

0.02%

0.5 V/V 7 ppb 35 ppb 142 ppb
1.0 V/V 14 ppb 71 ppb 284 ppb
2.0 V/V 28 ppb 142 ppb 567 ppb
Dissolved oxygen added to the beer during injection

So knowing all of this, what’s the best way to determine whether a CO2 supply is contaminated with air? There are two approaches. First is to simply measure your CO2 source in the gas phase using a low-level oxygen sensor that is accurate to at least 0.001%. The other is to measure the dO2 in your beer before and after CO2 injection. If you are measuring in the beer, use a measurement point that is furthest from the injection point so that the gas will have a chance to dissolve into the beer as much as possible before you measure. If you carbonate in a tank, just measure in the tank.

My final thought is that you may be doing everything right in the rest of your process, but if the CO2 you’re using to trim your carbonation is loaded with air, your beer may pick up a significant amount of oxygen.

Have you seen the article with the CO2 table? If you can point me to the journal and/or author, I’d be happy to post a reference.  Please leave the information as a comment below.

Frivolous Friday Fun – Ten Barrel Brew House in Ancient Egypt?

My wife Paula, an amateur Egyptologist, just brought to my attention a really cool article about a working brewery that was in full production in pre-dynastic Egypt.

So, okay — It may not match the sophistication of a ten-barrel brew house, but it looks like they could have brewed as much as 300 gallons a day. And keep in mind that this was roughly 5000 years ago – well before the first pyramid was even a glint in Pharaoh’s eye. Nice to know humans have always had their priorities straight!

Here’s the link

When to Measure Ambient Oxygen or Ambient Carbon Dioxide in Brewing Vessels

My first few posts to this blog have had mainly to do with measuring dissolved oxygen in beer, but while I was at the Craft Brewer’s conference earlier this month I heard quite a few questions about measuring both oxygen and ambient carbon dioxide in empty fermentation vessels and bright beer tanks, so let’s take a minute to talk about it.

There’s really always just one main factor in needing to know the amount of oxygen in an empty tank: you’re getting ready to fill it, and you want to minimize infusion of O2 into the beer.  Along those lines, if a bright beer tank is full of air and you want to blow it down with CO2 to minimize O2 contamination during filling, then knowing the level of O2 in the tank will tell you how well you’ve done displacing the air.

But there are two very serious reasons for needing to measure CO2 in an empty tank: either a fermentation vessel or bright beer tank has been emptied and you want to enter it before cleaning, or you plan to use caustic during Cleaning in Place (CIP).  If a person is going into a tank with high ambient CO2, they risk suffocation. And during CIP, excess ambient CO2 can actually set off an implosion and collapse a tank.

So think O2 if your concern is oxygen in your beer. But think CO2 to mitigate safety and environmental issues. CO2 can be really dangerous if you aren’t careful when you’re cleaning with caustic. I was at a brewery where someone had run a CIP cycle on a 1500 bbl tank that was mostly full of CO2. The tank imploded and scared the living daylights out of everyone. That’s an expensive and dangerous mistake.

My final thought is to measure the gas impurity rather then the purity. It’s a lot more accurate to measure trace level O2 than high level CO2, or low levels of CO2 than ambient oxygen. Environmental CO2 monitoring should look for – and find — only traces of CO2. Likewise, a bright beer tank ready to fill should have a very low level of O2.

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