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I've got some commercial yeast (fresh and compressed, the one in cubes) at home, which, as I've understood, is mainly made of Saccharomyces cerevisiae. My question is, is it possible to feed it and let it grow at home.

I don't want to make sourdough, though. I suspect that if I let it feed on flour, I'll contaminate it with lactobacilli. Can I feed it with some sugar (sucrose, for example)? Or should I just give up?

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    Does this answer your question? Culturing Yeast in Dough
    – LSchoon
    Jun 2, 2020 at 12:11
  • Also see cooking.stackexchange.com/questions/107887/…. Jun 2, 2020 at 17:08
  • I don't think this is a duplicate question, because here the aim is specifically not to allow lactobacilli (or other bacteria I assume) to develop. I don't think feeding just on sugar will make any difference: the bacteria are all around us, not something brought in by the flour. Sterilisation will of course just kill the yeast, so I cannot see any solution short of using specialised biochemistry equipment (a clean air laminar flow cabinet would be useful). Jun 2, 2020 at 17:38
  • @LSchoon, not really... The answer to that question explains how to make a less sour sourdough. Still helpful, but not what I was looking for.
    – Kyle
    Jun 2, 2020 at 18:20
  • @MarkWildon, I was thinking at something like making yoghurt: in that case there are some conditions (that are easy to create at home) that make the lactobacilli thrive while keeping the other bacteria at bay. I was looking for something similar for saccharomyces cerevisiae, but may they don't create such an hostile environment to the other microorganisms as lactobacilli do...
    – Kyle
    Jun 2, 2020 at 18:34

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You can try it on agar. Or you could imitate the industrial method. The industry uses diluted molasses and aerates the solution - yeast needs oxygen to multiply, in anaerobic conditions it does not multiply but converts sugars into alcohol. You could also try to sterilize the flour (pressure cooker / oven).

Note: air contains wild yeast cells and lactic acid bacteria. So the chances that they contaminate your culture is high.

Also note: if the culture is not well aerated, it produces alcohol, which in turn attracts acetobacter, which turn the alcohol into acetic acid.

When culturing mushrooms, the growers try to make sure that the selected mushroom strain is the one, that colonizes the substrate first, because it can then outcompete moulds and bacteria. I think if you have a high yeast ratio, it might be able to outcompete lactobacilli. This way you could probably use flour without having to worry that it turns sour.

Edit: lactic acid bacteria likes anaerobic conditions, in the presence of O2 it forms H2O2 which limits its growth. This could also be used to improve your LAB/yeast ratio.

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