Oxygen from welding tanks

I have been looking into a setup for oxygenating wort and notice some people use the disposable oxygen tanks you can pick up at home depot for welding. My question is, is this safe? I would take it the oxygen is not food grade and that since its for welding, if there were small amounts of other elements in with the oxygen, it wouldn't matter to the manufacturer. Is there food grade oxygen available?

I was also curious if anybody has tried using CO2 to prevent oxygenation in the secondary?. Sometimes you can lose quite a bit of stuff in the primary and end up with to much head space in the secondary. It seems that if you blew some CO2 in the carboy (not through the wort) to purge out the air before putting the airlock on this might help in preventing oxidation.

Welders don't want impurities in their O2 either but the truth is, all the gas comes from the same big tank. It would cost them more to keep two different grades separate.

Hey Brad,
I used to use pure O2, and I personally think it's an unnecessary expense. I am now aerating with an aquarium pump running through an air filter and stone. It takes longer with air, but I am getting much better fermentation now.

I think that I was harming the yeast with the O2, but I believe if I had used the O2 first and then pitched the yeast, I could have avoided that.

The welding O2 is OK to use.

I used to use that welding O2 with great results (not using it yet here as I'm still setting up the new brewery here in Croatia. But I *will* be using it.).

Someone posted this link in another thread. Thought it was a great link.

MB Raines, Ph.D. - Guide to Yeast Culturing for Homebrewers - Maltose Falcons Home Brewing Society (Los Angeles Homebrewing)

And from that, this:

In general, it is difficult for homebrewers to achieve sufficient oxygen levels. The levels of oxygen necessary for optimal fermentation vary depending on the yeast strain. Ale strains usually need between 8-12 part per million (ppm) while lager strains require slightly higher amounts (10-15 ppm). At atmospheric pressure the maximum level of dissolved oxygen in wort is approximately 8 ppm and the saturation level decreases further as the gravity of the wort increases. Thus unless special steps are taken to introduce air or oxygen into the wort, it is difficult for homebrewers to achieve adequate aeration. Recent studies have shown that oxygenation is by far more efficient than aeration. Injection of oxygen through a 2 micron diffusing stone can actually supersaturate the wort with 10-12 ppm of dissolved oxygen being reached in 5 gallons of wort by a single 60 second blast of oxygen!

Click to expand...

That being said, I agree that you can maybe hurt your yeast if you use too much. Search around and read and see what people say here about how long of a blast they gave it. As I recall, I think I was using something like 45 seconds to one minute with pure O2, but it was some time ago so can't be certain of my memory.