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31.03.2015 10:26    Comments: 0    Categories: Holidays      Tags: torah  passover  pessach  

What Essentially is the Prohibition against Hametz?

The main difference between hametz and matzah is explained in Parashat Bo (Ex. 12:39):

And they baked unleavened cakes of the dough that they had taken out of Egypt, for it was not leavened, since they had been driven out of Egypt and could not delay; nor had they prepared any provisions for themselves.

Had they wished the dough to be leavened they would have had to delay and allow the dough to stand. What change occurs during this standing that causes dough to become hametz?

It is generally considered that the main essence of leavening—becoming hametz—is the rising that takes place when the dough is left to stand. But it was not customary to eat fluffy bread in Mishnaic times, since most ovens were small truncated semi-ellipsoid structures in which bread was made by sticking the dough to the sides of the oven so that the heat of the oven walls, not the air in the oven, baked the bread. The bread would begin to get baked where it stuck on the oven walls, “so that the surface stuck to the oven would form a crust” (BT Shabbat 20a). Therefore, even after the dough began to rise it had to be rolled out again in order to stick it on the oven walls and bake it.

This enables us to understand the gemara (Pesahim 7a): “Rabbah the son of Rav Huna said in Rab’s name: If a loaf went mouldy, if matzah exceeds it [in quantity], it is permitted…if we do not know whether it is hametz or matzah…” In other words, if mouldy bread is found in the house and one does not know whether it is matzah or hametz, it is permitted if most of the bread in the house is not hametz.

Had it been the custom to eat fluffy leavened bread, not being able to distinguish from the shape of the bread whether it is hametz or matzah is inconceivable. Only because leavened bread was also rolled out, just like matzah, might one wonder whether or not bread that had moulded was hametz. Hence the main difference between hametz bread and matzah was not in its texture but in its flavor. Accordingly Iggerot Moshe[1] clarifies that the prohibition against hametz pertains to the flavor that leavening adds to bread. Only after Talmudic times did baking in what came to be known as “our ovens”[2] become widespread, where fluffy loaves were baked on a flat surface.

The fluffy texture of bread only became the most important matter, surpassing the issue of the leavened flavor, in modern times. Since rising bread by the action of yeast takes considerable time, other rising agents have come into use primarily with dough made of flour containing low protein levels, such as flour for home use. To explain the difference between these rising agents and yeast fermentation we shall begin by explaining the ancient process using yeast.

Kernels of wheat contain a protein called gluten. When wheat flour is mixed with water the gluten takes on the form of stiff elastic dough, which is the basis for shaping bread. The dough also contains around eighty percent starch. When yeast, an anaerobic microorganism, is mixed into the dough, it first breaks the starch down into sugar by means of enzymes that it secretes. Afterwards the sugar is changed in structure to glucose by means of another enzyme. The glucose can be “digested” by these microorganisms, which break it down in order to obtain the energy they need to live and multiply.

This anaerobic decomposition produces alcohol, carbon dioxide and water. Since each little particle of starch is encased in a layer of flexible protein—gluten—and part of the starch decomposes into carbon dioxide in the process of fermentation, a bubble of carbon dioxide forms inside the gluten case. In this manner the dough becomes filled with little bubbles and puffs up. If the dough is left that way and baked in an oven, the alcohol evaporates and the gluten hardens, as does any protein when sufficiently warmed, thus producing a loaf of raised bread that retains its shape.

The final raised form of the bread, however, is not the reason the dough becomes hametz. As we said, in Mishnaic times the dough used to be rolled out again and baked into pita-shaped bread. The benefit of the fermentation, when there was no interest in a raised loaf, was that the process produced not only alcohol, carbon-dioxide and water, but also other substances that gave the dough—and the bread baked from it—a special fermented flavor. These side-products are characteristic of the yeast and not of the dough; if we were to ferment grape juice using the same yeast organisms we would obtain exactly the same side-products and the wine thus fermented would have the taste and bouquet of yeast bread.

Therefore, in our day, having become accustomed to eating raised bread, the fermented taste is no longer important, either because other flavoring agents are mixed into the dough, or because people eat their bread with assorted toppings. Thus there is no need to make the dough rise by means of yeast fermentation. It can be made to rise using baking powder, which contains substances that form bubbles of gas when mixed with water and heated, so that the dough rises when put in the oven.

The advantage of the flavor added to dough leavened through fermentation is that the shelf-life of the resultant bread is extended. It is hard to eat a soft pita that qualifies as matzah after it has cooled. The show-bread—soft unleavened bread—was special in that it miraculously remained warm even seven days later, and therefore the priests were able to eat it: “Rather does this teach us that the table would be lifted up for the gaze of those who came up to the Festivals, with the mark: Behold how beloved you are of G-d, for it is as fresh when it is taken off as it was when put on, as it was said: ‘To put hot bread in the day it was taken away’” (Yoma 21b).

Leavened bread that received flavor from yeast was fit to eat long after it had been baked. Therefore people who wished to prepare food for a journey would see to it that they leavened their dough. But the process of leavening by yeast, which is a process of natural fermentation, requires much time and waiting. Therefore, the Israelites, who left Egypt in haste, unable to tarry and prepare themselves food for the journey properly, did not keep their dough long enough to give it the flavor of leavened bread, rather baked it immediately as matzah.

The Sages recount that miraculously these matzahs remained edible: “The pitahs that they took out of Egypt were eaten for thirty-one days.”[3] This is apparently the main reason why fruit juice is not considered to produce hametz, nor grains that are not considered dagan (sometimes rendered as “corn”; Pesahim 35a). Fermentation is generally associated with rot and stench, but in dough made from the five types of grain (dagan), fermentation is necessary in order to extend the shelf-life of the bread, as mentioned above. Dough that has been kneaded with the addition of wine, oil, or honey does not need to be fermented because of the flavor of its additives; likewise, baked good made of rice and legumes do not lose their flavor when they cool down. Hence there is no need to ferment them, and if they ferment it is simply considered rotting, not hametz.

In light of this, we must examine the statement in the Mishnah (Pesahim 3.2): “Dough which is hard [Heb. heresh, literally meaning “deaf”—when struck by the hand it produces no sound], if there be [other dough] of like nature that had become leaven, then this is also forbidden.”[4] Rashi explains:

Heresh dough—dough that one cannot detect whether or not it has leavened, for a person cannot ascertain. Alternatively: dough which is hard as heres, as a potsherd, and cannot be detected to have leavened, meaning that it has become silvery on the surface and shows no cracks as a sign of leavening. If there be other dough of like nature that has become leaven—this means if there is another batch of dough kneaded at the same time as the dough in question and that other batch has become leaven.

In order to make leavened dough by natural yeast fermentation one must add a quantity of dough containing a very high concentration of yeast to a new batch of dough. The former, which causes the latter to become leaven, is called se’or (“sour-dough starter”). If we do not add se’or to dough consisting only of flour and water, no process of leavening will take place in the dough, since the amount of wild yeast in the air is not sufficient to make the dough become leaven.

Even a small quantity of se’or will not make dough become leaven, as described in the case of se’or of terumah that is put in dough of hullin: “it never renders it forbidden unless it contains sufficient to induce fermentation.”[5] If there is such a thing as se’or that does not contain enough yeast to ferment dough, then clearly without any se’or one cannot produce fermentation in dough. Only if the mixture includes fruit juice that contains sugar can the wild yeast in the air ferment the sugar and afterwards also the dough mixture.[6] But dough made only of flour and water, without se’or, will not ferment even after a considerable period of time.

Take two pieces of dough, kneaded at the same time, and add se’or to one but not to the other. The dough without se’or will show no signs of leavening, since no real process of fermentation will take place. But the piece of dough containing the se’or will begin to show signs of fermenting after a period of time. The dough without se’or is heresh dough, and the dough with the se’or is the dough of like nature that becomes leaven. According to the Mishnah, also the dough without se’or is considered leaven, even though the changes that define fermentation did not occur in it.

The gemara goes on to ask: “What if there is no dough similar to it?—[The period for fermentation is] as long as it takes a man to walk from the Fish Tower [Migdal Nunia] to Tiberias, which is a [Roman] mile. Said R. Abbahu in the name of R. Simeon b. Lakish: For kneading, for prayer, and for washing the hands,…it is only a mile that he need not go back, but less than a mile he must go back.” (In other words, someone on a journey who forgot to perform these commandments must retrace his steps in order to perform them, provided the distance he need return is not more than one mile). When there is no other piece of dough to compare with the heresh dough, the dough in question is considered leaven if it has stood the length of time it takes to walk one mile (i.e., eighteen minutes). In this regard, the gemara states that the distance one must retrace one’s steps to wash hands or pray is one mile.

It appears that the definition of hametz pertains to the amount of time the dough stands, for the Torah states that the matzah was made of dough that was baked when there was no time to wait around. However, simply letting the dough stand is not logical, if that standing does not produce any benefit. The benefit in the dough standing lies in the improved flavor of dough that has fermented—and the Israelites were praised for not having tarried in order to enjoy this benefit.

But even if there were no benefit, only time elapsed, hametz is still forbidden by the Torah. The standing time is defined as the time elapsing between adding water to the flour, which is how one begins preparing dough, and baking the dough, which marks the end of its preparation. After it is fully prepared, there can be no more process of becoming leaven as defined, since there is no element of waiting. Flavor enhancement turns out to be at the root of the idea of letting the dough stand, and dough that changes in nature by fermentation is surely considered utterly hametz by the Torah, even if it stands for a very short period of time.

But even simply standing causes dough to become hametz. Both the one and the other (standing and flavor enhancement) are defined as applying only to dough whose preparation has not been completed, and not to dough that has been cooked or baked. But if the dough has not been left to rise but has been constantly worked, then the rule is that if it has changed by way of fermentation, that provides actual evidence of its having stood sufficiently long and therefore it is in every regard hametz. But if it has not changed in nature and we have seen that it was not left to rise, then there is no danger of it being hametz.

Working the dough is not just a matter of preventing the fermentation process by stretching the surface of the dough. Rather, working the dough prevents its being left to rise. Therefore, also working the dough that does not prevent fermentation, such as piercing the matzah,[7] forestalls the standing period. In any case the 18-minute time limit for standing is not tied to the process of fermentation itself, for if fermentation is evident in the dough this standing has no significance. Rather, the period of standing is considered substantial, as the gemara notes with regard to praying and washing hands, that the time lost in retracing one’s steps one mil is considered a substantial loss of time.

Likewise with kernels of grain, letting them stand in water can improve them for cooking, and in any case also such standing is forbidden. Therefore letting them stand [the time it takes to walk] one mile, which is a substantial period of time, causes them to be considered hametz. But if the kernels of wheat are stirred constantly while being moistened (even though such stirring is not supposed to have an effect on the rate at which the wheat kernels swell, since there is no process of fermentation here to be delayed by stretching the surface), the wetting and standing does not cause it to be hametz; therefore, by the basic rule one may eat flour made of such wheat on Passover.[8]

We conclude that the definition of hametz is not physiological, rather stems from the human perception of improving the taste of dough by fermenting it or improving grains by swelling it. Wherever there is such a process of enhancement, the fact of letting the dough stand is considered to produce leaven. But if there is no flavor enhancement or the dough is not left to rise, that is, if there are no signs of fermentation and the dough or kernels of grain are constantly worked, it does not become leaven.

Translated by Rachel Rowen

* Rabbi Shabtai Ha-Cohen Rappaport is head of the Beit Midrash at the Ludwig and Erica Jesselsohn Institute for Advanced Torah Studies, Bar Ilan University.

[1] Orah Hayyim, Part IV, vol. 6, par. 98, yesh.”

[2] Cf. Terumat ha-Deshen, Part I, par. 65, which explains the differences between ovens in the time of the Sages and ovens in later periods.

[3] Mekhilta de-Rabbi Ishmael, 16.

[4] Pesahim 3.2.

[5] Pesahim 27a.

[6] Cf. Menahot 54a: Our Rabbis taught: One may not leaven [the meal-offering] with apples.

[7] Cf. Shulhan Aruch 459, Taz 2nd siman and Magen Avraham 4th siman.

[8] Towards the end of par. 453.

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