I don’t remember for sure, but I want to say it is something like 15 ppm. I would not be surprised if it is strain and temperature dependent. It’s not really a concern because even if you can get that much in your wort, it will drop when you add the yeast. It is only a constant high level that is toxic IIRC. It is not a physical thing, it is a buildup of reactive oxygen species like superoxide and peroxide.
Are your DO meter readings accurate? The DO meters I used in laboratories had a built in stirrer because they did not work properly unless the water was circulating. I’m not sure what type of DO meter I was using or whether chemiluminescent DO meters need moving water to work properly.
Aha. Thanks for clearing that up for me.
The DO meter is in the glass carboy as it is being filled by pump, so it is always in well circulated wort. This is a very high quality Hach LDO. Even if it was off a point or two, doesn’t change the trend of sudden oxygen desaturation, of a high gravity wort, in very short period of time. I will run this experiment over the next several brew days to confirm this finding.
My current message to myself on this - I should pitch yeast immediately upon completion of wort aeration/oxygenation. My previous method was to fill the carboy, stop and do a yeast count, calculate my pitch volume, then pitch the yeast. This all the while the wort was desaturating…
Very interesting. Was about to buy a new o2 regulator with a flow meter, but now I’m not sure if its worth it. Have you done any more tests with this?