I finally got around to doing something I’ve wanted to do since the beginning: bake bread leavened with the yeast isolated from a sourdough culture. A few days before baking I started growing a starter of sorts. I did three steps up from a very small amount of yeast stored in isotonic salt solution. This is similar to what I do for beer but I stopped at about 200mL of weak broth (can’t remember if it was YEPM or MYPG; I forgot to label the jar when I made it). Once I had enough and it had settled I used a sterile pipette to suck up the sediment from the bottom, about 6 grams’ worth of loose, liquid sediment for a 500g dough. It rose overnight in the upper 60’s with a proof of about four hours the next morning. The tiny amount of yeast is in line with what I’d use with dry baker’s yeast for a long rise–it’s probably equivalent to a sixteenth of a teaspoon or so of active dry yeast. The dough is just flour, water, salt and yeast.
I figured it’d not be worthy of a post because it’d probably turn out exactly like a bread made with standard baker’s yeast. After all, it’s just yeast, with no lactic acid bacteria to create the sourness. To a great extent that is true, but the neat thing is that this yeast apparently produces a ton of diacetyl. I had noticed this before when using the sourdough culture it came from (my wheat starter) but I had for some reason assumed it was bacteria doing it. But when I took it out of the proofing basket today I got a massive whiff of butter. This made for a quite nice aroma while baking, although it seems to have completely disappeared in aroma and taste by the time the bread cooled.
These yeasts were the fastest growing (at least in terms of visible colonies) that I’ve seen so far. I suppose that’s consistent with what you’d expect from a continuously-refreshed culture like sourdough, but that’s just speculation. I have no idea what species they are, but I’m fairly certain it’s not S. cerevisiae based on the quick growth and colony characteristics. The colonies spread out much more than I’ve seen with S. cerevisiae. They are also whiter and flatter. I keep meaning to ferment wort with it to see its alcohol tolerance and sugar utilization but never get around to it.
DC Yeast Lab 