In my last post I touched on the topic of using a dissolved oxygen analyzer to measure the TPO in bottle-conditioned beer. The challenge is that you have to make the measurement before the yeast consumes any significant concentration of oxygen. Even if you do everything perfectly there will probably be some yeast consumption of oxygen, but taking the measurement quickly will get you a reasonably accurate measurement.
Speed is definitely your greatest asset in measuring the TPO of bottle-conditioned beer. Grab the package as soon as it comes off the filler and hustle it to the shaker. The faster you get it to the shaker, the quicker your dissolved oxygen value, and the less O2 the yeast in the beer will have had time to consume. Warming packages or waiting for any other reason will result in low readings.
How significant is the oxygen consumption if you wait? When I first started taking oxygen measurements in bottle-conditioned beer I didn’t understand how active yeast could be. Our typical protocol was to take three bottles off the packaging line and shake them, one after the other, for three to five minutes, depending upon the packaging temperature of the beer. What we found was that the first package was always highest, with each subsequent container lower than the previous.
Since there was no way this could be statistically possible, we started to look for ways to minimize the O2 uptake and get readings that at least followed proper statistical scatter. The best way was to take one package of beer at a time straight from the filler to the shaker. Taking three at a time was messing us up, because by the time we shook the third package – even if it was only 15 minutes post-filler – the yeast had consumed a significant amount of oxygen. The same thing applies if you are measuring unshaken packages for some reason. Any time you deal with bottle-conditioned beer, quickness is important.
There are analyzers that will take headspace and liquid measurements of beer, but they cost a lot more than a simple dO2 analyzer. Calculating TPO from a dissolved O2 measurement can work well, as long as you get a reasonably accurate dO2.
My final thought about measuring bottle-conditioned beer is that even though yeast consumes the oxygen in your beer, leaving you with a lower residual level in your package, that’s not necessarily a good thing. Exposing yeast to too much oxygen can leave you with off-flavors down the road. The best practices of the industry are to treat dO2 control in bottle-conditioned beer with the same care as filtered beer.