By Torah law only the five species of grain (wheat barley oats spelt and rye) can become chometz and they are also the only species of grain with which one can produce matzoh that one can eat to fulfill the obligation on the Seder night.[i]

The Rambam[ii] writes explicitly “But kitniyos such as rice millet and the like do not become chometz. Even if a person kneads rice flour with boiling water and covers it with cloth until it rises like leavened dough it is still permitted for consumption because this is not leavening but spoiling.”

The Gemara[iii] does quote a minority opinion of Rabbi Yochanan ben Nuri who maintains that rice is also considered a grain but his opinion is not accepted as halachah — as the Gemara concludes[iv] “No one is concerned by the opinion of Rabbi Yochanan.”

The earliest source for the prohibition of kitniyos on Pesach is found in Rabbeinu Peretz’s emendations on the Smak[v]: “With regard to kitniyos ... and the like our teachers observe a prohibition against consuming them on Pesach and that seems to be correct … My teacher Rabbeinu Yechiel used to eat white beans on Pesach … He would prove [that they are permissible] from the fact that even with regard to rice which Rabbi Yochanan ben Nuri considers a species of grain with regard to chometz the Gemara states that no one is concerned by Rabbi Yochanan’s opinion. However it is very difficult to permit something which the practice has been to prohibit since the days of the early sages.”

Rabbeinu Peretz concludes that we should uphold the custom prohibiting all kitniyos not because they are actually chometz but as a gezeirah (rabbinic injunction) for the following reasons: (a) since kitniyos is a cooked food and grain is also a cooked food if we were to permit kitniyos people might become confused and permit grain foods as well; (b) there are places where people make bread from kitniyos and unlearned people might become confused and make bread from one of the five species of grain.”

Many of the Rishonim who lived shortly after Rabbeinu Peretz quote the prohibition of kitniyos and attribute it to him.[vi]

Although some initially opposed the stringency it has become an accepted part of Pesach observance among Ashkenazim who will not eat many types of legumes such as rice millet broad beans lentils beans soy peas and chickpeas. It is generally accepted that the definition of kitniyos with respect to this prohibition is not the same as the botanical definition of legumes. Rice and corn for instance are botanically defined as grains and are nevertheless prohibited as kitniyos. On the other hand some species botanically classified as legumes are not subject to this prohibition.

In addition to the reasons cited by Rabbeinu Peretz poskim have advanced the following explanations for the prohibition:

1)                  Kernels of actual grain might have become mixed in with the kitniyos.[vii]

2)                  Kitniyos do become leavened and are called chometz (such as chimtzi chumus).[viii]

3)                  It is not appropriate to consume kitniyos on Yom Tov since the Torah requires us to rejoice (Devarim 16) and the consumption of a cooked dish of kitniyos does not engender joy.[ix]

4)                  There is a type of deformed wheat that resembles grains of kitniyos.[x]

5)                  Some attribute the prohibition to a stringency that was adopted to promote perishus.[xi]

Based on the reasons for the prohibition we can understand why the definition of kitniyos is based not on its botanical definition but rather on the degree to which it corresponds to the various concerns behind the prohibition. [xii]

The poskim mention the following species among others as being subject to the prohibition of kitniyos: rice millet broad beans lentils beans soy peas and chickpeas. Sesame seeds are also included in the prohibition [xiii] since they are also considered kitniyos.[xiv]

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