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In this week’s parsha we find two distinct commandments regarding Pesach, one to eat matzos and the other to refrain from eating chametz.

As part of my work at the Showbread Institute researching the Lechem Hapanim, it has been my privilege to participate in cutting-edge research into the concept of “chametz,” in collaboration with Bar Ilan University and the world’s current leading authority on the subject, HaRav Shabtai Rappaport, shlit”a. I would like to share with you some of the groundbreaking results of this new research, from sefer Meir Panim, relating not only to the science but also to the philosophical perception of chametz.


Let’s begin with the halachic definition of chametz.

When grain or flour from the Five Species comes into contact with water for 18 minutes or more, they undergo a process called chimutz, and the resulting product is called chametz.

The Five Grains are “commonly” considered to be wheat, barley, spelt, rye and oats. The first two, wheat and barley, are undisputed. There are different opinions regarding the last three grains, a discussion of which is beyond the scope of this article.

There is no single word in any other language that adequately reflects the essence of the Hebrew word “chametz,” and terms like “fermentation” are deficient at best and even misleading, as we will soon see. The terms “chametz”; “se’or”; and “machmetzet” in the text are interchangeable.

Halachic sources provide visual “markers” that allow us to identify whether dough has become chametz or not. The first are telltale cracks on the surface of the (stiffer) dough, referred to in the Gemara as “karnei chagavim,” thin cracks resembling grasshopper antennae. These cracks on the dry, outer surface of the dough are a result of the dough rising and stretching. The second is a silver sheen on the surface of the (more liquid) dough, referred to in the Gemara as “hichsifu panav.” This phenomenon results from the formation of alcohol as part of the fermentation process, which reflects light differently from water. If either (or both) of these visual cues are detected, even if 18 minutes have not yet passed from when the flour came into contact with water, that is sufficient to halachically rule that the dough has become chametz.

A “grey” area exists when these visual cues are absent, or cannot be definitively observed. This type of dough is called “batzek cherish,” a “deaf/mute” dough, thus named because its visual appearance does not clearly “communicate” to us whether or not it has become chametz. In this case, the Sages defined a specific period of time, 18 minutes – the time it takes to walk the distance of a mil (approximately one kilometer). In other words, if 18 minutes have passed since the flour and water came into contact, even if none of the above visual cues are observable, the dough is halachically regarded as chametz.

Numerous studies have been conducted in an attempt to identify chemical “markers” that allow us to scientifically determine when dough becomes chametz. While these have uncovered many interesting characteristics and similarities (for example, the Five Grains are the only grains that have gluten proteins – except perhaps for oats, which is disputed), science has thus far been unable to get to the bottom of chametz.

On a chemical level, chametz is a conundrum. The existence of fermentation is not sufficient to define chametz. For example, if flour of the Five Grains were to come into contact with another liquid besides water, like fruit juice, for 18 minutes or more, fermentation certainly takes place, but the dough is not considered chametz even after an hour or two of such fermentation. Similarly, if water is combined with flour from a grain not of the Five Grains, like cornmeal, fermentation also takes place but is not considered chametz. These two examples belong to a different category, “sirachon,” which is identical to chametz chemically but not halachically. Chametz has thus so far defied both translation and scientific quantification.

Perhaps the only way we will ever be able to understand the essence of chametz is on a philosophical level. There are many erroneous interpretations regarding the fact that chametz bread is “inflated” while matzah is not, inferring that “inflation” in bread is something negative and impure. Proof to the contrary is Lechem Hapanim, a matzah devoid of chametz which is nevertheless inflated to the thickness of four fingers (a tefach).

A more accurate way of understanding chametz on a philosophical level has nothing to do with gas or acidity but rather with idleness. Dough that becomes chametz is dough that is allowed to rest – to become inactive and flaccid. Contrast this with dough that is constantly active, like the dough Am Yisrael took out of Egypt, strapped to their belts during the two or three day journey from Raamses to Sukkot where they baked it. Three days are certainly more than 18 minutes and even so, their dough did not become chametz because it was constantly being jostled and kneaded as they walked.

The Sages liken chametz to the evil inclination (yetzer hara). The concept of chametz comes to teach us that as in dough that is left to become idle chametz forms and takes control, similarly, if we allow ourselves to become idle and lack diligence in performing G-d’s will, the evil inclination will gain control over us. Matzah is the antithesis of idleness. It is typified by frenzied activity from beginning to end and symbolizes devotion and diligence in our service of G-d.

Parshat HaShavua Trivia Question: How do we know the matzah Am Yisrael baked after they left Egypt was round in shape?

Answer to Last Week’s Trivia Question: Why were only the barley and flax destroyed by the locusts and not the wheat? Barley and flax are spring crops. The plague of locusts took place around Pesach time, in the spring. Wheat ripens in the summer, around the time of Shavuot, so it was not affected by the locusts.


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Eliezer Meir Saidel ( is Managing Director of research institute Machon Lechem Hapanim and owner of the Jewish Baking Center which researches and bakes traditional Jewish historical and contemporary bread. His sefer “Meir Panim” is the first book dedicated entirely to the subject of the Lechem Hapanim.