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.