The Science Behind Chometz and Other Matzah Halachos

Yeast Intolerances - what you should and should not eat ...

by Rabbi Yair Hoffman for

The world is filled with micro-organisms called yeasts that surround us.

They are found everywhere – on the ground, on plants and trees, on human beings and even in the very air that we breathe. These airborne yeasts enter everywhere. They even enter into Matzoh dough, and feed upon the starches that are in the flour. The yeasts produce carbon dioxide. The carbon dioxide expands the gluten proteins in the flour. This is how dough eventually becomes Chometz.

The Gluten protein is the composite of two other chemical gliadin and glutenin. These gluten proteins are elastic. When the yeast break down the starches into alcohol and carbon dioxide, the dough begins to expand and to rise. The elements that help in the expansion of the gluten proteins are warmth, water and time. The yeasts produce more efficiently when there is warmth.

Another factor that is not so well known is the concept of atmospheric pressure. The higher the elevation, the lower the surrounding pressure and the more the carbon dioxide will expand.


Weather patterns in Eretz Yisroel and near Egypt are very different from that of Europe and the United States. In Eretz Yisroel there are only two rainy seasons. There are virtually no rains otherwise. In Europe and in America it rains constantly.

Because wheat that has ripened fully can become Chometz while yet attached to the ground, one should cut the wheat while it is still green (See SA 467:5 and MB 453:22). This halacha is applicable in Europe and the United where it rains regularly. In Eretz Yisroel, however, the custom is to cut it later.


There are two type of Matzos: Matzos Mitzvah and regular Matzoh. Matzos Mitzvah are those Matzos that are two be used on the nights of the Seder in fulfillment of the Mitzvah, “In the evening you shall eat Matzos..”

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Matzos Mitzvah can technically be baked from wheat, barley, oats, spelt, and rye. However, it is ideal, a Mitzvah min haMuvchar, to bake them from only wheat (Ramah 453:1 and MB 453:1).

The posuk states “Ushmartem es HaMatzos” (Shmos 12:17) – which literally means, “and you shall guard the Matzos.” Our sages extrapolated from this posuk that these Matzos require a special supervision that it not become subject Chometz. In other words, it is not enough to just assume that nothing happened to them. Rather, ideally, the wheat of which a person wishes to make Matzos Mitzvah must be guarded to ensure that there is no concern of them becoming Chometz. This guarding is called “Shmurah.”


It is interesting to that obtaining Matzos for Pesach is not just a hechsher Mitzvah – a preparation for a Mitzvah. It actually involves this Mitzvah in and of itself – that of “ushmartem es haMatzos – guarding the Matzos.” This is indicative in the language of the Shulchan Aruch (OC 460:2).

The Mogain Avrohom (460:1)writes that it is ideal to bake the Matzos oneself because of the notion of Mitzvah bo yoser mib’shlucho – it is a greater Mitzvah to do something oneself than through a messenger.

The Avnei Naizer (OC 472) decries the prevalent custom of people no longer baking Matzos themselves. The Mishna Brurah cites the view of the Arizal that one who works up a sweat through baking Matzos receives enormous merit.

Although it can be done through an appointed messenger or shliach, just buying the Matzos off the supermarket shelves is not the best way to fulfill this Mitzvah.
There are thus three methods in how people obtain Matzah.

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• They either are deeply involved in the baking.

• They appoint a messenger to bake it for them (which can be accomplished through an order sheet).

• They buy it off the shelf (not the best way).

There is, however, a workaround for the off-the-shelf purchaser. If time is spent examining whether there are folds or bubbles in the Matzah that would render the Matzah unfit, then one does fulfill the special Mitzvah of guarding the Matzos.

The Matzos must be made for the sake of the Mitzvah. If the Matzah is made without the proper intentions, there is a debate among halachic authorities whether one can fulfill the Mitzvah with that Matzah. This debate is found in the Biur Halacha (460 “Ain.”) The Pri Magadim rules that one does not fulfill the Mitzvah. The Ritvah rules that in regarding to kneading and baking one can assume that there is the proper intent when done without thinking. This is not the case, however, with harvesting and grinding.

If there is a halachic doubt concerning either the flour or the Matzos, even though they would be permitted through the principle of “Rov” that they are from a majority which would permit them or through the principle of “Sfek Sfaikah” a double-doubt, – they should not be used for Matzos Mitzvah – the Matzos on the seder night. This is the ruling of the Bais Meir which is cited authoritatively (MB 467:17).

The Science Behind Chometz and Other Matzah Halachos 1

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