I asked a question earlier about kettle souring using helium to purge the O2. I'm out on that idea, but somewhere I read that you could cover the top of the wort with plastic wrap to keep oxygen out. I'm assuming by laying sanitized wrap directly on top of the liquid during souring, before the boil.. Does that seem doable? Keep in mind I don't have a CO2 setup. Heck, there's not anybody within 100 miles that can fill a CO2 bottle. Thanks in advance!