The role of oxygenation in beer fermentation
Once our beer is brewed we do anything to avoid exposure to it, but during the brewing, particularly in fermentation, it is absolutely necessary. We are of course, talking about oxygen.
Fermentation is the step in the process where the sugars are converted into alcohol and carbon dioxide — essentially, when the wort becomes beer. Oxygen, necessary for sustaining life on Earth, is also a key element in ensuring efficient fermentation.
However, dissolved oxygen in beer impacts haze and flavour stability, and can lead to an off-flavour — the enemy! This means it is a delicate balance to control oxygen levels.
Firstly, temperature impacts oxygen solubility in the wort, lower temperatures reduce oxygen levels so maintaining consistent fermentation temperatures is key to controlling these levels.
Yeast, the engine of fermentation, needs oxygen to breathe just like we do. So aerating the wort is vital for yeast growth, sugar consumption and therefore, alcohol production. Oxygen enables yeast to synthesise essential compounds in fermentation.
Now yeast is as picky as the rest of us and needs different conditions to work at its best. Different yeast strains have varying oxygen requirements — these fussy critters need between 10-12 ppm oxygen to thrive. Generally, ale yeast requires more oxygen than lager yeast. So it can be said, that proper yeast handling and storage adds to maintaining yeast health, which in turn contributes to oxygen control. Let’s not forget whilst the yeast needs oxygen, introducing residual oxygen to our beer leads to off flavours. So, oxygen control becomes very important — restricting oxygen ingress is taken very seriously throughout the brewing process.
There are means to ensure this doesn’t happen — closed systems with no leakage possible, maintaining positive pressures during transfers and a headspace blanket — basically a layer a gas like carbon dioxide or nitrogen to prevent oxygen entering the fermentation vessel. All measures to control the oxygen the final beer is exposed to.
At PMG, all of our tanks go through rigorous factory acceptance testing to be sure that all inlets, outlets, manways and sample valves close tightly. Further to that, each tank being finished with ultimate precision and high-grade silicon O-rings and seals will ensure no oxygen can enter the vessel accidentally.
