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.
This is the third and final attempt at plating out the whole sourdough starter. I did a few things differently:
- I fed the three sourdough starters and let them ferment for 12 hours before starting. Last time two of the starters were right out of the fridge.
- I put even less of each culture in the sterile water to dilute it
- I used bromocresol green + potato dextrose plates, plus one potato lactose plate
The rye starter’s plate grew mold in a few days. It totally took over before I had a chance to see anything else growing. The other two starter’s plates plus the lactose plate (on which I plated the wheat starter) were totally fine. I let them grow out for 16 days.
Clockwise from top left: brown rice flour starter, wheat flour starter, wheat starter on potato lactose plate
The colonies look translucent and shiny from certain lighting angles, but they are off-white, smooth and round and actually matte. I did not see any flat colonies like last time. The weirdest surprise is the almost identical growth on the lactose plate. I am going to assume that this is due to whatever sugar was in the potato and not the lactose. My goal in doing so was to see if I could get the bacteria to grow on there and was not expecting the yeast to grow at all. You can see very tiny colonies on each of the plates between the large yeast colonies and smaller yeast colonies. They are transparent and shiny. I believe these are the lactic bacteria.
I think I may not have used enough bromocresol green, or the plates were old enough that it had already started to fade. I was expecting green colonies here, too, but they were white. On my first (recent) attempt I did see green colonies but the plates were also darker back then. The colonies looked quite similar between the two starters. This is a change from the first time I did this (earlier in the year) but could be because I am using a different medium.
I picked out a yeast colony from each and plated it on YEPM medium (recipe from jaapie’s site; the ingredients are not cheap or easy to find for hobbyists like me). In the past, the yeast I isolated from the wheat starter didn’t appear to ferment maltose whereas the rice starter’s did. We’ll see if these grow on it (from what I can tell, yeasts generally but not always can grow on something they can ferment and vice-versa).
On another note, I finally resumed the DCambic project from April. I had isolated a yeast from it back then but it appeared to not do much besides make lots of strong fruit esters. Notably, it didn’t seem to produce any alcohol. This time I instead went for growing it in liquid first instead of plating directly from the sample. I now seem to have two different types of yeast in liquid, judging from the two colors of sediment I see. A darker sediment formed first. I then started shaking to aerate the culture on a regular basis for a few days and then added this to more sterile wort, which I similarly shake on a regular basis. I am now seeing a lighter color sediment forming as well. I also see lots of evidence of fermentation, though I did not see any krausen at any point. I shook up the culture yesterday and streaked a sample on a PDA plate. I’m hopeful that this time I can get the yeast that produces the distinct Bretty aroma I can smell from the culture.
These are the results after 5 days of growth.
Wheat flour starter (Carl’s Friends) on top. Bottom left is the brown rice flour starter (homegrown) and the right is the immature rye flour starter.
I am a bit surprised for a few reasons. First, from looking at them I was convinced that there was no yeast growth. At first I had all three of them in a big plastic bag, and the smell was not at all yeasty. It also looked like all of the colonies on the wheat and brown rice starters were very glossy like bacterial colonies. I had previously plated both of those on malt extract agar and the yeast colonies looked very different from each other, but definitely looked like yeast. I saw nothing of the sort here. The rye starter definitely had nothing that looked like yeast, but it is still young.
The first surprise came when I opened the tops to photograph them. I first took some of the colonies from the wheat starter plate and put them in a bit of light wort. But when I took a whiff both the wheat starter plate and rice starter plate smelled very yeasty. The smell from the bag I mentioned before was from the rye starter plate. It smelled not wholly unpleasant. I could pick out acetic acid but there were other things underneath. The colonies were tiny and slightly yellow. I’m not sure if they were heterofermentative LAB that produce acetic acid or some sort of enteric bacteria.
In the end I tossed out all the plates. But now looking at the picture above I can see that the colonies aren’t equally glossy. On malt extract agar (a long time ago) the wheat starter’s yeast were flat, dull and bigger than brewer’s yeast. That kind of matches some of the colonies I see in the picture. The rice starter’s yeast looked and behaved a lot like brewer’s yeast (I planned on trying it for brewing but never got around to it. I just made some small liquid cultures.) I don’t see anything of the sort here.
Later today I’m going for a third try on the bromocresol green and dextrose plates. Hopefully I can get some distinct yeast growth since LAB aren’t supposed to grow on it.