If I had to pick the one question I hear most often from brewers, it would be this: how much dissolved oxygen (dO2) – defined as an absolute quantitative measurement — can I have in my beer before I’ll get premature oxidative flavor changes? I’m often asked this in the form of a question about successful brewers and their dO2 levels. But since that information is always kept in strict confidence, and we don’t need specific examples anyway, let’s just talk about it from an historical perspective.
I started making Total Package Oxygen (TPO) measurements in 1989. Back then, many brewers were still using air counter-pressure in their bottle fillers, so it wasn’t unusual to see values between 800 and 1700 ppb. Today, TPO levels in breweries with good oxygen control are below 60 ppb in bottles and 100 ppb in cans.
In mid 1996, my work led me to measure dO2 in the other brewing processes. Beer after filtration or centrifugation ranged from 30 to 300 ppb, and finished beer ranged from 30 to 500 ppb. Today, in breweries with good oxygen control, those values range from 5 to 25 ppb.
Flavor changes due to oxidation are one of the few things over which a brewer has control. By regularly monitoring dO2 throughout your process, you can determine which pumps, valves, filters, centrifuges and other ingress points are contributing unwanted oxygen to your product. If you’re a small brewery, then watch for two culprits: your process during the addition of filter aids, like diatomaceous earth (DE,) and inadequate blowing of storage vessels.
By de-aerating their DE slurry and blanketing the mixer with N2, one brewery reduced their dO2 pickup from 350 ppb to 30 ppb without any other process change. Monitoring oxygen in a CO2 blanketed tank is a good idea too. And are you worried about an old filler that has no CO2 evacuation? TPO pickup in the filler can be decreased to almost nothing if a liquid nitrogen doser is used before the packages are filled with beer.
My final thought is about my own beer drinking experiences and how good dO2 control has shaped what I purchase. When I first started drinking craft beer in the late 1980s, the beer quality was erratic. Once I’d been trained in sensory analysis, I learned the differences were mostly due to oxidative flavor changes, and so I’d make a point of actually trying to read the date codes to avoid getting older beer. As my favorite breweries got their oxygen levels under control, the inconsistency of their product decreased, and I no longer need to worry about squinting at bottles to ensure I was purchasing great beer.