Most of the time when I feed my sourdough starter I find uses for the discard, but on occasion I don't have time or good ideas, so I put it in a separate jar and store it, with a tight lid, in the fridge. Yesterday I took the discard jar out and found something I've never seen before: a layer of dry, off-white, stringy material (see photo), with the distinct smell of baker's yeast: suspected yeast layer on top of sourdough discard

Hooch often appears in the discard jar after a few days, but this is definitely not that. It also doesn't look like any type of mold I've ever seen - and definitely doesn't smell like it either.

Luckily this is just the discard jar and not my active starter, but I'm really curious. Could this be yeast? If so - where could they have come from? And how have they grown on top of a lively sourdough culture?

N.B.: I had made this starter from scratch (i.e. flours and water) without using yeast or any other additives, and have never seen this in the 6 months I've been using this culture

  • 1
    I agree with FuzzyChef's comment. + I would add, that you can dry out sourdough if you can't find a use for it. This is a traditional method for storing it.
    – G. B.
    Commented Oct 19, 2020 at 13:30
  • @G.B. oh don't worry, I have plenty of use for the sourdough starter itself, this was just some discard from a weekday feeding while I was rushing to work :)
    – Oded R.
    Commented Oct 21, 2020 at 17:50

1 Answer 1


Sourdough culture is partly yeast. Since this container was made up of sourdough taken out of your primary culturing vessel, and not fed, that is probably dead yeast that floated to the top. After all, it hasn't had any source of sugar since you put it in the fridge.

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