About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.
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Here's a problem I hope someone will find interesting. I learned recently that you can grow your own yeast to make sourdough bread. All you have to do is mix together some flour and water, and keep it warm. I decided to try that, and now I have a bowlful of flour, water, and something that keeps makes bubbles in it. But there are a couple issues I could use some hints with. Just for reference, I posted this to the forum Sourdough Bread Australia, which was started very recently.
The mystery is that, after being kept near 85 degs F for 3-4 days, the mixture started smelling like paint. Then, after dilution/feeding with more flour & water, and possibly dropping a few degs, it smelled more like fiberglass. Apparently the smell of paint is caused by dibutyl and diethyl phthalate, and the smell of fiberglass is primarily from styrene (ethenyl benzene). Something certainly seems to be growing in the bowl, but the flour I'm using is bleached, and lactobacilli live symbiotically with yeast. So there's plenty of uncertainty about what exactly is causing the odors. My current amateur theories are:
1) Some really bad strains of yeast that were the only ones to survive the bleaching .
2) Way too much lactobacilli from a somewhat high temperature.
2) Interaction of something with some form of chlorine or other preservative.
But I also have counterarguments to each theory:
1) In the first 12 hours after mixing, the mixture had a nice sourdough bread smell, so maybe it's just a good yeast gone bad.
2) The temp was kept carefully within normal limits well below 90 degs F.
3) Many recipes ignore the question of bleach in the flour and supposedly do okay.
So there you are. The pleasant sourdough smell that occured early is the desired norm. My hope is that the good yeast is still present or available, and any bad yeast or other organism present can be suppressed under appropriate conditions. Any clues? I have only a crude grasp of organic chemistry, so please be gentle. Thanks much in advance.
The identity of the microbe(s) is one of my main questions. The yeast (hopefully) is captured wild, as found in the flour (see theory 1) and/or the air. My hope is that the nature of its metabolic products offers some suggestions as to what it most likely is.
Of course, all the smells are subjective. The early smell was subjectively enjoyable, the later/current smell subjectively feels like it's going to dissolve my brain, which I would like to avoid if at all possible. I just started a second sample with high-protein, unbleached bread flour, we'll see how that works. But if the rogue microorganism is present in the air, it might pose a continuing risk, and it would be nice to know what parameters might be varied to discourage it, whether they be temperature, wetness, bleach, pH, oxygen, or anything else.
Hmm, not much response. Okay, here's another question. Suppose you have a thick slurry or paste of flour and water. Lots of starch, moderately wet. Now store it at 50F/10C. What sorts of organisms will thrive or at least survive best in that environment? My impression is that bacteria will do poorly, but what about molds, or anything else? What will be favored most or suppressed the least?
Different species of bacteria thrive across broad temperature ranges - some will be perfectly happy at 50 degrees. Individual varieties may have a narrow range for growth, but almost all ecological niches are filled. (Some even live in hot springs.) Think about food left in the fridge for too long - you will see growth of both bacteria and molds. Most microbiologists are concerned with either human pathogens (which do best at 37 degrees C) or the bacteria found in soil and water which thrive at 'ambient' temperature so our perception can get skewed.
FWIW - sourdough is normally made with a mix of rye and wheat flour - not plain wheat. That may be one reason your mix went astray. Starters rely on wild yeasts and bacteria in the air more than in the flour - which is why you cannot readily duplicate San Fransisco sourdough in New York. If you don't do much baking, or have odd bugs growing in your kitchen (from growing mushrooms, or making cheese, yougurt, beer or vinegar) there is no telling what might have taken over. You could take a sample of the starter, dilute it in water and look at under a microscope. It isn't hard to tell the difference between bacteria and yeast. A Gram stain would shed additional light on the possibilities.
The papers below may have more technical info than you want, but are interesting research on sourdough.
http://www.pubmedcentral.nih.gov/articl ... tid=309968
http://www.faqs.org/faqs/food/sourdough ... on-38.html
Thanks a lot. I'll take a look at the first two, I have the third. I wouldn't be at all surprised about the flour being responsible. It would be interesting to know the reason(s). As for where most of the organisms come from, there are lots of different theories. I can't tell which ones to believe.
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