These days one hears much about the "Holiday" of Passover and even we Karaites refer to it often. But in the Hebrew Bible there is no such holiday! In the Tanach "Passover" is the name of a sacrifice, while the holiday is called Chag HaMatzot ("Feast of Unleavened Bread"). Thus in the verse: "Draw out and take a lamb according to your families, and slaughter (KJV: kill) the passover." (Exodus 12:21). In this verse the "Passover" is the lamb that is to be sacrificed by slaughtering and eating it. Similarly in Exodus 12:26-27:
"...when your children shall say to you, What mean ye by this service? And you shall say, It is the sacrifice of Yehovah's passover"
The service of slaughtering the lamb and eating it is called "the sacrifice of Yehovah's passover". This is also the meaning of Passover in the verse: "In the fourteenth day of the first month between the two evenings is Yehovah's passover" (Leviticus 23:5). And again in Deuteronomy 16,1: "Observe the month of the Aviv, and perform the passover unto Yehovah your God". To "perform" or "keep" the Passover (in Hebrew literally "do the Passover") means to bring the Passover sacrifice and eat it. It is only in post-Biblical times that the word Passover took on the new meaning of referring to the Holiday on which the sacrifice was eaten and not to the sacrifice itself. Today we often hear of the "Passover Holiday" and "Chag Ha-Pessach" both of which are post-Biblical inventions. In the Tanach the Holiday is called Chag HaMatzot which means: "Feast of Unleavened Bread".
What is Leaven?
There is a centuries-old debate among the Karaites themselves about the definition of Hametz (leaven). According to the first opinion Hametz is the process of leavening that occurs to certain grains when they are mixed with water. The test to identify what types of grain can become Hametz is to take the flour of that grain, mix it with water, and leave it for a few hours. If the dough rises, that grain is subject to becoming Hametz (leaven). On the other hand, if the dough spoils, then that grain or plant is not leaven-able and it can be freely used and cooked on Passover.
This seems rather obvious but in the Middle Ages the question arose of whether lentil-flour was permissible on Passover. While lentils are not grains, their flour looks much like wheat-flour. The Rabbanites too puzzled over this issue and to this day Sephardic Rabbanites eat lentils on Passover while Ashkenazic Rabbanites do not. Rather than accept arbitrary rulings the Karaite sages sat down and performed experiments. They concluded that the flour of lentils does not rise but spoils and therefore lentils in all its forms are permissible on Passover. The same with rice which is also permissible in all its forms on Passover. Adherents of this view include most of the medieval Karaite sages including Aharon ben Eliyah and Elijah Baschyatchi (see below) as well as the present author.
Not all Karaites agree with this definition. The second school of thought argues that Hametz is not strictly speaking "leavening" but something like "fermentation". They point out that in biblical Hebrew vinegar is called "Hometz Yayin" meaning "leavened-wine" (others translate: "soured wine"). This is used as proof that Hametz refers not only to the leavening of grains but any fermentation or souring process. Based on this reasoning, they forbid the consumption of anything fermented. Included in their list of forbidden foods on Passover are all forms of alcohol, and all milk products such as yogurts and cheeses. Some, although not all, include lentils and rice in this list of forbidden items. This school also considers wine to be Hametz, which is somewhat surprising given that vinegar is called "leavened-wine" (implying that the difference between wine and vinegar is that the latter is leavened but the former is not!). Adherents of this view include the medieval Karaite sage Samuel al-Maghrebi.
The following are excerpts from the writings of some medieval Karaite sages on Hametz:
"and the sage our teacher Yosef Kirkisani said... only the five types of grain can be made into Hametz, namely wheat, spelt, barley, oats, and rye. And the sage was correct because whatever experimentation shows to leaven can be used for Matzah, but the flour of the other 'seeds' do not leaven. For example, [the flour of] millet, rice, beans, lentils, and peas do not leaven but spoil [lit. 'stink']." [Aharon ben Eliyahu (14th Century), Gan Eden, pp.45d-46a].
"The sage Yosef Kirkisani said that only the five types of grain can be made into Hametz, namely, wheat, spelt, barley, oats, and rye. It has also been said that if experimentation shows that a thing can become leaven then it can be used to make Matzah. However, all the other 'seeds' such as bean, lentil, pea, millet, and rice flours do not leaven but spoil [lit. stink]. And the sage our teacher Aharon (author of Etz Hayyim) said that all of these matters can become known through experimentation and he has spoken well for millet flour if left with water for a number of days does leaven. Therefore, in truth, there are six types of grain that can leaven and from which Matzah can be made: the aforementioned five as well as millet. And if Hametz is made from any of these it must be destroyed... and so too any alcohol made from the five types of grain [e.g. beer] or from millet. But some of the fools in our times who pretend to be wise do not eat anything that ferments based on the verse 'no leaven shall you eat' such as fermented milk [i.e. yogurt, etc.] and fruits soaked in water; they also refrain from eating beans and rice and any type of 'seed' and this is because of their foolishness and their lack of knowledge..." [Elijah Baschyatchi (15th century), Aderet Eliyahu, Ramla 1966, pp.133-134]
See also the treatise of Samuel al-Maghrebi in Karaite Anthology.
Have a happy and Kosher Chag HaMatzot!