Something that always nagged on me is how much oxygen is really getting into my stir plate starters. I just pitch the yeast, toss the starter on the plate, and expect it to work out. I either cover the starter loosely with foil or using a foam stopper. I figure this must allow some gas exchange as it’s a popular system, but to me, intuitively it would seem once the oxygen in the head space is dissolved and consumed, not a whole lot would replace it. Perhaps if it was a wide mouth container, there would be a greater exchange, but I’m not so sure with these Erlenmeyer flasks.
So, I tried something different. I got a couple starters going this week, but this time I put a hose from my aquarium pump into the head space. The pump has a sterile filter, and the starter is loosely covered with foil. In theory here, the pump will push sterile air into the head space and excess will vent out. The spinning of the stir plate will absorb fresh O2 constantly. An alternative could be to just use an air stone, and perhaps skip the stir plate all together, but I think there would be lots of foaming. So, I just put the tube to deliver fresh air to the head space rather than the starter itself.
This might be excessive, but I can’t see it hurting. Worst case I’m just entertaining myself. I don’t have anything real concrete for results, but just visually there might be something here. I’ll keep playing around with this and maybe I’ll do some experiments. I was thinking of decanting off the starter into graduated cylinder and comparing yeast volumes.
Anyone else try anything like this?
UPDATE 07/02/08: I did three batches w/ this technique with so far positive results. I did a stout, Alt and a lager at 67, 60, 50 degrees, respectively. All three had quick starts and vigorous fermentation. It seems this technique produces more viable and vital yeast than just the stir plate alone. I’m curious how they turn out.
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Injecting O2 into a stir plate starter