After starting off my home brew in the kitchen, I move it downstairs to the store room, which is rather cooler. The lower temperature seems to have been a problem for the wine yeast I used last year, and I have a dozen demijohns full of half-fermented wine. I'm hoping it will get going again when the weather warms up, but I'd prefer yeast that doesn't need much warmth to ferment.
I'd been thinking of buying lager yeast, as that works at lower temperatures than most, but then I had another idea: The wild yeast that I'm using as a sourdough starter seems quite happy in cool temperatures (i.e. winter kitchen temperatures) and I've heard of people getting yeast from sourdough for cider; maybe I could do the same for beer.
I added extra water and left the starter until it separated out, then drained off the cloudy liquid, leaving as much of the floury gloop behind as possible. I don't really want starch in my beer. I added this to my usual heather ale recipe and left it to see what would happen. The quantity of yeast cells in that bit of liquid was probably pretty small, so I gave it longer than I usually would to check for signs of life. That is, I checked for bubbles frequently, but gave it three days before giving up.
Last autumn, I chucked a couple of crab apples in a jar of sugary water in the hope of cultivating wild yeast from the apple skins. The jar was still sitting on the kitchen counter, smelling... possibly alcoholic, possibly just appley - certainly not foul. I poured that in. A day later, I added some more of the sourdough starter, this time being less fussy about the starch. Eventually, I saw tiny which flecks on the surface - little bubbles? I monitored further until it became obvious that the white fleck were not bubbles, but some kind of growth. Oh, *%! That is not the kind of life I was hoping to see.
However, before throwing it all out, I did a bit of research, and learned a new word: Pellicle. This is a layer that forms on top of wort during the brewing of beer. It's the same kind of thing as the scoby that forms in kombucha brewing, but not the same micro-organisms.
While the cultivated brewing yeast doesn't form a pellicle, other strains of the same species can do, so it's entirely possible that wild yeast might do so. My pellicle smelled a little musty, but not too strong or foul. I also poked a dropper through the surface to take a sample of the wort, and that tasted fine, so I left it to see what would happen. A day later, I saw bubbles under the surface.
Bubbles indicate fermentation, so there's definitely something going on, though of course, I don't know what kind of fermentation. It still smells OK, so I'm going to wait and see what develops. At worst, I'll get something that smells and tastes horrible, and I'll have to throw the whole lot away. Alternatively, it might taste of nothing, which is also not worth keeping. Another possibility is that mainly acids are forming, in which case I might have two gallons of vinegar, which is not ideal, but worth something. There's also a chance that I might end up with a delicious and unique beer. I'll just have to wait and see.