Chametz - What Is Chametz? - The Five Grains

The Five Grains

For the rabbis, five specific species of grain become chametz after wetting. The actual species are not known with certainty, although they would necessarily have been crops that grew in the middle east in Biblical times. When the Bible was translated into European languages, the names of food grains common in Europe, wheat, barley, spelt, rye and oats, were used, some of which were not grown in ancient Israel:{Mishnah P'sachim 2:5}

As more accurate historic and botanical evidence comes to light, some scholars today propose that only the 'five grain species' native to the Land of Israel can become chametz. They are:

Shippon (shifon) – einkorn (Triticum monococcum),
Kussemet – emmer (Triticum dicoccon),
Chittim – durum wheat (Triticum durum) and bread wheat (Triticum aestivum),
Se’orim – six row barley (Hordeum vulgare), and
Shibbolet shual – two row barley (Hordeum vulgare).

Spelt, rye (Secale cereale), and oats (Avena sativa) did not grow in the Land of Israel in the biblical period. Since spelt (Triticum spelta) is genetically closely related to bread wheat it is also considered to be prohibited. Rye should not be eaten since it closely resembles wheat and can be mistaken for it; it was considered chametz during Exile, even though in fact it did not grow in ancient Israel and was not on the list of chametz-capable grains. According to the Talmud, when any grain not listed is exposed to water it begins to "decay or rot", rather than "rise" (sirachon).

Coincidentally, these are also the grains that people with celiac disease or gluten intolerance must avoid.