Dissolved Oxygen in the Brewery
At first brewers knew nothing about the invisible forces that operate in the brewery. They knew certain things had to be done in a particular order, at given temperatures, under certain conditions etc to make good beer.
We now know a lot about yeast and beer spoilage bacteria and the invention of microscopes meant they were no longer hidden forces but could be directly seen and measured.
But one invisible force still haunts the brewery: oxygen. Oxygen is the driving force in staling reactions that more than anything else affect the shelf-life of beer. The fresh hop aroma is the first to go. The flavour becomes duller and unpleasant flavours start to appear, like a persistent caramel sweetness that can throw a beer off balance, and a cardboard and papery flavour. Haze starts to form.
Oxidising staling reactions are temperature dependent and can be minimised by careful storage, but when the beer leaves the brewery there’s no way of knowing how it will be looked after in the long distribution chain that takes it to the final consumer.
DO (Dissolved Oxygen) is the new brewer’s bogeyman and we’re essentially back in the shoes of our ancestors trying to deal with it.
At Boyne Brewhouse we practise a number of measures to ensure that as much as possible the beer you receive is as fresh as the day it leaves the brewery.
The most important is purging all pipework and hoses before moving from one tank to another. A meter long length of one of our hoses contains a litre of air. A litre of air contains 300mg of oxygen. Industry best practice guidelines would be to ensure final in package dissolved oxygen levels of less than 50 parts per billion. Our batch size is 3000 litres. If the air content of a meter of one of our hoses bubbled into a tank, that would add 300mg to 3000L or 0.1mg/l or 100 parts per billion, i.e. double the allowance for the whole batch!
For this reason, we fill all hoses with water before and after transfer between tanks. We pre-purge all tanks with expensive CO2 prior to transfer to ensure the beer is kept in a low DO environment.
It’s ridiculously painstaking stuff, but it’s worth it to ensure that the beer stays fresh as long as possible.
Cheers to fresh beers!
Andrew Jorgensen, Head Brewer