OXYGEN INJECTION OF WORT
By Mike Retzlaff
In the 9/2018 issue of the Hopline, there appeared an article reprinted from BEERSMITH HOMEBREWING NEWS entitled “Aeration for Home Brewing”.
As explained in the article, wort boiling removes most of the dissolved oxygen. Yeast must have at least some oxygen in solution for the initial aerobic phase of fermentation. In very basic terms, yeast requires O2 at this point to replicate. Once the little yeast beasties are crowded shoulder to shoulder, they start eating the wort sugars in earnest. If you’ve ever had a ferment that seemingly lasted for weeks on end, it is probably because if insufficient initial aeration.
The article went on to explain your options in aerating the wort which include splashing, agitation, and injection. The injection can come in using an air stone with an aquarium pump & filter or using pure O2 with a stone.
The Brewers Publications book “YEAST” confirms that the desired level of oxygen saturation is 8 – 10 ppm as was stated in the article. In a test conducted by White Labs, the following levels were achieved:
Shaking for 5 minutes 2.71 ppm
30 sec. pure O2 5.12 ppm
60 sec. pure O2 9.20 ppm
120 sec. pure O2 14.08 ppm
Their recommendation for the home brewer with a 5 gallon batch is 1 liter per minute of pure O2 for one minute through a 0.5 micron sintered air stone. Exceeding the recommended 8 – 10 ppm results in a somewhat quicker ferment for the first few days but the terminal gravity does not change. Under saturation of the wort results in a terminal gravity of a full degree Plato higher than properly aerated wort and it usually takes longer to get there.
Early on in my brewing, I started out with shaking and splashing the cooled wort. I upgraded to an aquarium pump & filter with an air stone. It definitely improved my brewing but I couldn’t seem to keep the air stone from clogging (yes, I did all the stuff everyone preaches like boiling the sintered stone, not touching it with bare fingers, etc.). At the Brew Offs I saw O2 injection in action and really liked the idea. Due to the generosity of a friend, I got an oxygen cylinder and regulator. I now use the White Labs recommendation of 1 liter of O2 per minute for 1 minute. I hang the sintered stone at the bottom of the fermenter, turn on the O2, and stir the wort while the O2 is flowing. Of course this is in conjunction with a stir plate generated starter.
If you are interested in upgrading your equipment to include this technique, you might think about hitting a few yard sales. Somebody’s Grandma or Grandpa may have passed away recently and their O2 equipment may be there and gotten for a very reasonable price. All you need after that is an air stone on a wand and perhaps a change of plastic tubing. This equipment can come in the form of an O2 tank or an Oxygen generator. In any case, O2 injection is the best and easiest way I’ve found for this very important step.
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