We continue in chapter 10 of Maseches Menachos, mishnah 7, with the discussion of the prohibitions of chadash - the produce of the new year. As we learned, the prohibitions of chadash apply specifically to the five species of grain identified by the Sages: wheat, barley, oats, spelt and rye.
The source of the law - the gezeirah shavah of "lechem" "lechem":
The basis for the fact that specifically these species are subject to the prohibitions of chadash is a gezeirah shavah, a shared word that teaches a shared definition. Regarding chadash the verse says: "And bread, parched grain and fresh ears you shall not eat" - a prohibition against eating bread, meaning loaves and other grain products. The concept of "lechem," bread, appears with regard to matzah as well, which is called "lechem oni."
Matzah is made specifically from these five species of grain, since they are fundamentally capable of becoming chametz. They contain certain proteins - gluten and gliadin - which serve as a kind of molecular scaffolding that makes leavening possible. Other species, such as rice, lack these proteins: even if you ferment them, there is no scaffolding to allow the bubbles of fermentation to raise the dough, and it remains flat. It emerges, then, that the five species fit for making matzah are the very same five that are subject to the restrictions of chadash - the gezeirah shavah of "lechem" "lechem."
The mitzvah of challah:
Another mitzvah from the Torah is the mitzvah of challah, concerning which the verse says: "And it shall be that when you eat of the bread of the land, you shall set aside a portion for Hashem." That portion separated from the dough is called challah. Since the verse defines this as the eating of bread, it is understood that the doughs obligated in separating the portion given to the kohen are specifically those made from the five species of grain - the same species from which matzah, called "lechem oni," is made.
An entire tractate is devoted to the mitzvah of challah, and most of its details are explained in their own place. Here the mishnah mentions in passing that this is the same list of five species that are restricted both with regard to chadash and with regard to the obligation to separate challah.
The words of the mishnah:
"HaChittim" - wheat.
"V'haSe'orim" - barley.
"V'haKusmin" - spelt.
"V'shibolet shual" - oats, as it is rendered in practical halachah.
"V'haShifon" - rye.
These five species of grain are "chayavin b'challah" - there is an obligation to separate challah from them when the dough contains the required measure. That measure is the isaron, the same quantity of flour we spoke about in connection with preparing the menachos. In practice this amounts to between two and a half and five pounds of dough, roughly nine to thirteen cups of flour, and this is the measure from which one begins to separate challah with a berachah.
The mishnah continues: "u'mitztarfin zeh im zeh" - if dough was made from two kinds of flour, a little wheat and a little barley, or spelt and rye that were mixed together with water and kneaded into a single dough, the combined quantity joins together to reach the measure, which the mishnah in Challah calls five quarters of a kav, and which is the isaron we spoke about. It is worth noting that all of this applies on condition that they were kneaded together; but if the doughs were made separately and only afterward joined to one another, the matter of combining them is more complicated, and only certain kinds of grain combine, and this is not the place for it.
That same list of five species is also restricted "mile'echol chadash milifnei haPesach" - from eating chadash before Pesach. "Pesach" here, in the straightforward understanding, is a shortened reference to one of two things: to the passing of the sixteenth of Nisan, the second day of Pesach, or to the bringing of the omer on that day. The mishnah means to say that the new produce restricted on account of chadash consists specifically of these five species, and not other crops - rice, millet and the like - growing in the backyard.
They are also restricted "milik'tzor milifnei ha'omer" - from harvesting before the Omer. As we mentioned in the previous Mishnah, the Omer offering is called "the first of your harvest," and therefore it must be the first to be harvested; no other grain may be cut before the barley used for the Omer meal offering is harvested. There are several exceptions to this rule, and we will address them in the coming Mishnayos.
What determines which year the grain belongs to?
The answer is the moment the grain takes root. "Im hishrishu kodem la'omer - ha'omer matiran" - if the grain took root before the Omer was offered, the Omer permits it to be eaten this year, even though it is still growing in the ground. "V'im lav - assurin ad sheyavo omer haba" - a plant that had not yet taken root when the Omer was brought, the grain that grows from it is not permitted until the following year's Omer is brought on the second day of Pesach.