I was once reading the ingredients on a pack of Bissli (with a Pesach hashgacha) and saw that it contained yeast. How can this be?

  • 2
    Bissli has a Wikipedia page!?!? +1
    – MTL
    Commented Sep 30, 2014 at 4:44
  • @Shokhet, I would have used Osem's page, but I couldn't find it. PS. many treif snacks have Wiki pages. Commented Sep 30, 2014 at 13:42
  • Aside from the question of maris ayin for its similarity to chametz bissli (though for some reason this seldom seems to be a concern of the kashrus industry).
    – Loewian
    Commented Sep 30, 2014 at 18:05

3 Answers 3


Yeast is not Chametz.

Chametz is defined as the five grains rising.

Yeast, on the other hand, is made from potato:

In general, yeasts are grown in the laboratory on solid growth media or in liquid broths. Common media used for the cultivation of yeasts include potato dextrose agar or potato dextrose broth, Wallerstein Laboratories nutrient agar, yeast peptone dextrose agar, and yeast mould agar or broth.

  • What about Se'or?
    – Double AA
    Commented Sep 30, 2014 at 5:43
  • 3
    @DoubleAA Se'or is your sourdough starter. It still contains flour and water.
    – Shalom
    Commented Sep 30, 2014 at 13:58
  • You'll also see "torula yeast" in some ingredients. Papermakers have "wood soup" in need of disposal, and the torula yeast eat the nutrients in that. Win for the papermakers, win for the yeastmakers, win for kashrus because pine is kosher l'pesach, pareve, lamehadrin!
    – Shalom
    Commented Sep 30, 2014 at 14:00
  • @Shalom but perhaps that should be explicated in the answer...
    – Double AA
    Commented Sep 30, 2014 at 15:36
  • 1
    You can also have grape yeast for winemaking. Commented Sep 30, 2014 at 16:12

Yeast are single celled microorganisms that are classified as Fungi and can be found on everything. There are many sources of yeast which do not come in contact with chometz and therefore are not a concern for pesach such as grapes and other fruits and vegetables.


Leaven is a chemical interaction between any of the 5 grains wheat, spelt, oats, barley, or rye and yeast. (And, technically, what we today call oats isn't the original oat, not "shibolet se-orah" as it was back then. It actually doesn't ferment like the other 4, so we likely lost a species along the way an substituted.) Yeast alone is not leaven, as wheat and water baked quickly enough is not leaven, as the yeast in the air hasn't enough time to leaven it, and no yeast is otherwise added.

  • But what about Se'or.
    – user9907
    Commented Jul 1, 2016 at 17:06
  • I think you mean shibbolet shu'al, and whether that means oats is an ongoing dispute. Commented Mar 2, 2017 at 18:17

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