At present I oxygenate my wort inline during cooling with pure (?) O2 as I assume it to be as close to sterile as possible in a homebrew situation and hence more practical than working with an aeration stone and aquarium pump after cooling to pitching temp. Although I have not experienced any problems with fermentation, I wondered what your views on it would be regarding yeast health etc.

Thank you for devoting some of your valuable time to answer questions on the HBD.

-Jurriaan Boekamp

RESPONSE:

Both methods of introducing oxygen into the wort are satisfactory as long as you keep the dissolved oxygen in the 8 -15 ppm range. The oxygen transfer rate from an air bubble into the wort is very poor. The oxygen transfer rate from an oxygen bubble is very good, so it is much easier to over oxidize the wort using pure oxygen that it is using air. The pure oxygen technique requires careful monitoring, using a very fine stream of bubbles.

A small excess of oxygen results in an added increase of yeast cell mass which is not bad but not desirable. It will effect the ester formation slightly. A larger excess of oxygen can place an oxidative stress on the yeast cell, producing an unhealthy cell with possible undesirable by products. The yeast has a mechanism called glutathione reductase to protect itself against excessive oxygen.

The aquarium pump method is inexpensive but carries with it the possible sanitation problem. Good sanitation practices can take care of that. The pure oxygen technique is a Cadillac method but requires close monitoring. You have been successful thus far. Apparently you have mastered the correct timing and flow rates.

A colleague of mine has always been leery about hospital grade pure oxygen. He noted that some hospital grade O2 contains a fungicide. He uses industrial grade oxygen. For your interest. The best time to introduce oxygen into the wort is on the second day of the fermentation. The yeast need it the most at this time. Some commercial breweries are beginning to adopt this technique. Double batch fermentations automatically adds oxygen on the second day.

Dr. Clayton Cone