A canister like that lasts me maybe 10 batches, maybe more. I’ve never actually kept track I just know that it lasts for a long time, and that includes giving a shot to my starters as well. I always disconnect the regulator when I’m not using it.
I made the mistake at first of dumping the o2 in too fast and blowing through canisters. Be sure you are just trickling it through. If you dump it in too fast you are wasting it anyway as most o2 will just pour out of the surface and not diffuse into the wort.
I get about 20 batches out of mine, I’m on my 3rd bottle. They seem to last forever. Only open the regulator enough so the bubbles just make it to the top of the wort, 2 minutes worth. 30 seconds for a big (4L) starter. I remove the regulator when not in use.
I have a red O2 bottle from Home Depot and push it through a 2 micron stone. The bottle “felt” empty when I bought it and it feels the same today after 5 or 6 batches. I always trickle the flow and keep the regulator off when not in use.
There is no way to gauge the volume left. Maybe a spare bottle would be handy.
I always remove the regulator from my O2 bottles. If it’s empty after two or three batches you either have a leak or you are using WAY too much O2.
I put the stone by the side of the carboy so I can see the O2 coming out and adjust the flow so that there is just a trickle. I don’t know how many batches my last bottle lasted, but at least 10. It was also an extra large bottle, but not that much larger.
Thanks for the replies, all. I had been cranking the regulator all the way open, so it looks like no surprise that I was running through them so fast. The instructions that came with the kit from the LHBS weren’t very detailed. They did tell me to keep a spare bottle on hand, so I’ve never been short of O2.
And I’ll take the regulator off when not in use. I suspect that doesn’t have so much to do with it, but fewer parts that can fail = lower probability of failure.
20 Batches is about right. If you are getting less than that, you are doing it wrong. Oxygenate, long and slow. If you see more than a hint of bubbles at the wort surface, the flow rate is too high. “Blasting it” is another way of saying “wasting it”.