Ask the Brewmaster

Charles Potter asks this month's questions:

In stepping up from the "shake the carboy method" of wort aeration and not wanting to go to all the expense of pure oxygenation, there seems to be two mid-level alternatives: (1) the aquarium pump aeration system, that takes about 30 minutes or (2) a siphon sprayer attached to the end of the wort outflow on a counterflow chiller setup. See http://www.northernbrewer.com/page19.htm for a setup for both. It appears the siphon sprayer is a cheap way of doing this and a time saver too as it is combined with the wort chilling process. I'd like to go this route but I have never heard of anyone doing this effectively. Does anyone have any recommendations?

Oxygen, as most brewers know, is a critical component to the early life of yeast. Yeast cells require oxygen for initial growth and reproduction. The boiling process drives out oxygen. Hence, fresh oxygen must be introduced into wort at pitching time.

Oxygen has a rather limited solubility in wort, so it takes a bit of effort to get enough in. Time and surface area are both needed to get there. Eventually, the process will max out. When using air, the solubility limit is about 9 ppm. Surface area can be generated either with bubbles (such as with a pump and diffusion stone) or by spraying (as with the siphon sprayer. Our fearless leader (no good nickname yet) can personally vouch for the pump method. I don't know anyone that has used the siphon sprayer, so I can't vouch for its effectiveness. (If anyone has, please let me know.) However, my hunch is that you'll need quite a bit of pressure to get a good spray. This means you'll have to get the wort kettle up pretty high to make it work. Also, be aware that it will reduce the flow rate through your chiller. The spray will cool the wort somewhat, but don't run it too hot. If you run it at or near boiling temperature, you'll oxidize some of the malt. The beer will then age prematurely, leading to a stale taste. Running it moderately warm is OK, but bear in mind that oxygen has lower solubility at higher temperature.

The fact that air only has 21% oxygen limits the saturation. Pure oxygen, on the other hand, will let the concentration rise to about 45 ppm. Hence, for best results, go with the oxygen bottles.

Regardless of your method of choice, everything must be sterile. Boil the diffusion stone and hoses, and make sure that you put in the HEPA filter. The old-fashioned shaking method avoids the hassle of sterilizing extra parts. Since the process maxes out, shaking will give you just as good a result as the pump or spray system. If you don't want to jump to the pure oxygen system, it's probably best to stay with the shaking method. I do.