Soaked some decomposing oak leaves for 36 hours in preboiled water with some yeast flakes. Stirred, put 1-2 ml into test tubes with 5 ml of malt beer (“Karamalz”, I just picked a random brand), filled up with equal amounts of 5 % vinegar and whisky (didn’t have any vodka at hand). Put a thin layer of neutral vegetable oil on top.
Should keep out the vast majority of bad microbes and provide a mostly oxygen free environment for yeast.
IIRC, I’ve also read on suigeneris brewing that oak leaf litter has a 50 - 80 % chance of catching bretanomyce, which I’d be thrilled to find.
Interesting idea. I’d heard of just putting oak bark in beer as that essentially confirms that the yeast can survive in those conditions!
What’s the thinking behind the yeast flakes? I presume you mean the Hefeflocken you get in German grocery shops? IIUC this is baked yeast cake so shouldn’t have live yeast to compete with the wild ones but perhaps provides nutrients?
I can see how the oil might help stave off kahm yeast but won’t you need oxygen at first to help the wild yeast multiply?
Depending on the brand, ready made beer can be pretty high on hops, inhibiting some desirable microorganism growth, and pretty low on easily accessible sugars. I think it can still work, but the success rate will probably be low.
Here, I provide a medium rich in sugars, low on hops, with some acetic acid and alcohol - all selecting against the majority of stuff that I don’t want.
I’m not the expert here, but from what I gather the yeast flakes provide amino acids and such. Yeast nutrient would have been better but that I also did not have on hand. And yes, it’s Hefeflocken, exactly.
The oil on top is there too inhibit mold. Yes, for multiplying, yeast needs oxygen, but there will be some dissolved already I guess. After all though, this is more of a selection than multiplication step.