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As far as I know the most common yeast starters are malt extracts which are sealed with an airlock. But the few times I worked with yeasts in the lab we used YM-Medium (Yeast extract-Malt extract) to cultivate different yeasts, including S. cerevisiae. Anybody knows if it would be desireable to do the same if brewing? Or would it leed to an unpleasent taste?

Typical YM-Medium:

  • Yeast Extract.................................3.0 g/L
  • Malt Extract...................................3.0g/L
  • Peptone........................................5.0g/L
  • Dextrose........................................10g/L

I assume it would have the best outcome regarding the devision rate.

Additionally many people seem to put an airlock on the flask prohibiting O2 of diffusing into the flask. Wouldn't it be better to put a cotton gauze plug on the flask so it is proplerly aerated (with a stirrer) while being protected from infections? Or is it somehow desirable to have the yeast fermenting instead of its areobic phase?

Thanks a lot in advance!

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1 Answer 1

It's generally recommended that you decant starter wort before pitching. As long as you do that, it doesn't seem you should get any off flavors from it. I simply put some foil loosely over the top of the jug I make starters in.

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FYI, Denny's use of the foil instead of the airlock achieves the same thing as the cotton gauze mentioned in the question: gas exchange during the propagation is definitely desirable. I think some folks cap their starter vials/jugs with an airlock out of fear of contamination, but tin foil or some other breathable plug seems to work just fine. –  Graham Nov 5 '13 at 14:38
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