Application Note: Measurement Of Dissolved Oxygen In Wort

Wort is the liquid produced by extracting sugars from germinated barley (malt) with boiling water. The wort is cooled, and after aeration and addition of yeast, it is allowed to ferment to produce beer. Although it is generally desirable to keep oxygen (O2) out of the brewing process, at the fermentation stage it is necessary to actively increase the dissolved oxygen content.

Yeast requires O2 to synthesize the unsaturated fatty acids and sterols necessary for life and growth. The amount of air or oxygen required depends on the gravity of the wort, the yeast strain used and the brewery design.

The dissolved oxygen content may be adjusted from time to time depending on the yeast performance and beer quality. The normal dissolved oxygen range is 7-14 parts per million (ppm). For high gravity brewing operations 15-20 ppm of oxygen is required for fermentation, it is now common practice to make and ferment worts with a relatively high initial extract content (gravity e.g. 16 °Plato) mainly for financial benefit.

Hot wort is cooled with a plate heat exchanger (called a wort cooler) and is virtually air free (having been boiled). Yeast will be added to the wort, and for the yeast to grow it is necessary for the wort to contain high levels of O2.