yesterday i finally got to do a properly controlled experiment to confirm for my own little nerdy self the DO levels from shaking vs. injecting pure O2. purchased 20 cubic foot O2 cylinder from local welding supply, it's roughly the same size as a 5 lb CO2 cylinder. also purchased regulator, you cannot use a CO2 regulator on O2 tanks. DO meter was borrowed from my assistant brewer who works for a company that sells safety equipment and lab supplies, incl DO meters, he confirmed for me that the meter had been calibrated at their shop two days before.
10 gallon batch cooled to 68F pitch temp, OG of 1.066, split into two buckets. for first bucket*, i did my old standard down-on-one-knee bucket sloshing with frequent burping until blowoff hole in lid was no longer visibly pulling a suction between burps. probably sloshed at good clip for four minutes? then removed lid and tested with meter, reading showed 7.97 ppm of DO. this jibed remarkably well with what i had read, that the theoretical max for agitation-method is about 8ppm. (someday i'd like to build a mechanical agitator and give it like 30 minutes and see how much higher it goes.) for second bucket i used pure oxygen. previously i had played around with the airstone submerged in bucket of sani water to get a sense of what would be a good psi to see on the regulator. i decided on 13.5 psi. with the airstone sunk to bottom of the ferm bucket, i turned on gas and timed for two minutes. DO meter read just over 8ppm. i gave it another 60 seconds and it read 12.20 ppm. the literature i've seen mostly converges on 10 ppm as a good minimum DO for ale worts. too much O2 is, i think, only really a concern for packaging breweries who don't want any lingering O2 in the bottles to cause staling and stability issues. i'm a pub brewer so i don't care if i'm a bit above 10ppm.
* sloshing bucket (the first tested) was actually the second filled. evap rate from boil was higher than expected so i ended up with probably only 4 gal in the sloshing bucket, which is an important here to the DO test conducted because you can slosh the liquid a heck of a lot better when it's only 3/4 full than when it's almost completely full.
next step will be to add my flow meter to the oxy tank rig. i picked up a cheapo thorpe tube style flow meter from welder supply for @ $15. with this i will have a quantitative sense of how much oxygen by volume i'm actually using in those 3 minutes. if it's crazy high, like 1/4 of the tank or whatever, i'll experiment with using lower psi for longer time.
another test i'd like to conduct is the aquarium pump method. this is attractive since air is free. only downside is having to come back and remove aeration after an hour or two or however long it happens to take. also, i'd probably want to rig up some type of filtration for air, so that's further assembly time. but i have a friend with a degree in microbiology and he's pretty confident that for brewing purposes, i could use a pretty simple filtration method, like an inline pvc pipe filled with cotton balls that i've spritzed with alcohol.
pic of 2-micron airstone used: