Science Friday: How to Prevent OxidationAug 30, 2013 Comments (0)
Oxidation goes hand-in-hand with beer aging (which you may remember a blog post about earlier). The amount of oxygen sealed into the bottle or keg has a direct impact on how long until the development of the aged off flavors begin to show in the beer. The flavors associated with age generally come across as a cardboard, malty aroma and a papery, tea-like, dried dark fruit flavor.
Brewers are very aware of the negative effects of oxygen on beer and go to great lengths to minimize its concentration in the bottle, can, or keg. There are a couple instances where knowledge of oxidation can be useful to you, the beer drinker.
The first instance is when filling or buying a growler. It is important to keep the beer cold, but filling a growler it is difficult to get the low levels of oxygen that you would find in a bottle, can, or keg. This means that you want to consume the growler as soon as possible. If a growler is left alone in the fridge for a week, it will taste noticeably different than when it was fresh from the tap. Another big consideration is once you pour the first beer from that growler, the clock starts ticking. A significant amount of air rushes into the growler to fill the space the beer took up and that air gets to work on your beer quickly. If you drink half a growler and put it back in your fridge for a day or two, you risk coming back to flat, papery-tasting beer.
The second instance is when you buy a keg for a picnic with a pump tap (think back to the type of taps on kegs at college parties). These taps work by pumping air into the keg to maintain pressure and allow the beer to pour properly. While these work well for parties and BBQ's, they are not a good long-term solution for beer dispensing. If you are using one of these tap systems, you can pretty much guarantee the beer will not taste very good beyond the day that you tap it.
We take preventative measures to make sure each pint and bottle you drink is free of oxidation. One of the ways that we can catch oxidation early is by making sure our beers are free of high Oxygen content. We test for Oxygen by using a Gehaltemeter (German, literally meaning “stuff meter”). We use it with pressurized nitrogen forcing the beer sample through the center piercing needle, into the Gehaltemeter. The Gehaltemeter then tests the beer for oxygen by luminescence. The Gehaltemeter emits a blue light which excites an oxygen-sensitive layer. From this excited state two thing can occur. Either there is no O2 present in the beer and the excited electrons fall from the excited state to emit a red light, or there is O2 present in the beer and the excited electrons collide with the oxygen to emit no light at all. The higher the O2 amounts, the lower the red light intensity is and that rate is measured. We never allow a beer with over 100ppb (parts per billion) oxygen levels leave the brewery!