Pesachim 56a~ The Snake as a Symbol of Healing

In much of the Talmud snakes are associated with coma, convulsions and death.  But occasionally - and paradoxically -  they are sometimes associated with those healing, and those who heal. Let’s begin with this page of Talmud.

פסחים נו, א

תָּנוּ רַבָּנַן: שִׁשָּׁה דְבָרִים עָשָׂה חִזְקִיָּהוּ הַמֶּלֶךְ, עַל שְׁלֹשָׁה הוֹדוּ לוֹ, וְעַל שְׁלֹשָׁה לֹא הוֹדוּ לוֹ. 

עַל שְׁלֹשָׁה הוֹדוּ לוֹ: גָּנַז סֵפֶר רְפוּאוֹת — וְהוֹדוּ לוֹ. כִּתֵּת נְחַשׁ הַנְּחשֶׁת — וְהוֹדוּ לוֹ. גֵּירַר עַצְמוֹת אָבִיו עַל מִטָּה שֶׁל חֲבָלִים — וְהוֹדוּ לוֹ

The Sages taught: King Hezekiah performed six innovative actions. With regard to three the Sages agreed with him, and with regard to three they did not agree with him.

With regard to three actions the Sages agreed with him:  He suppressed the Book of Remedies, and they agreed with him.  He ground the copper snake through which miracles were performed for Israel (Numbers 21:9), destroying it because it had been used in idol worship (II Kings 18:4), and they agreed with him…

You might have heard that the symbol for healing, that snake (or is it two snakes?) wrapped around a central pole, came from the episode to which today’s page of Talmud is referring. In Numbers 21 the Children of Israel complain that “there is no bread and no water, and we have come to loathe this miserable food.” So God sends fiery snakes “that bit the people and many of the Israelites died.” Let’s let the Good Book tell the rest:

7-10 :במדבר כא

וַיָּבֹא הָעָם אֶל־מֹשֶׁה וַיֹּאמְרוּ חָטָאנוּ כִּי־דִבַּרְנוּ בַיהוָה וָבָךְ הִתְפַּלֵּל אֶל־יְהוָה וְיָסֵר מֵעָלֵינוּ אֶת־הַנָּחָשׁ וַיִּתְפַּלֵּל מֹשֶׁה בְּעַד הָעָם׃

וַיֹּאמֶר יְהוָה אֶל־מֹשֶׁה עֲשֵׂה לְךָ שָׂרָף וְשִׂים אֹתוֹ עַל־נֵס וְהָיָה כָּל־הַנָּשׁוּךְ וְרָאָה אֹתוֹ וָחָי׃

וַיַּעַשׂ מֹשֶׁה נְחַשׁ נְחֹשֶׁת וַיְשִׂמֵהוּ עַל־הַנֵּס וְהָיָה אִם־נָשַׁךְ הַנָּחָשׁ אֶת־אִישׁ וְהִבִּיט אֶל־נְחַשׁ הַנְּחֹשֶׁת וָחָי׃

וַיִּסְעוּ בְּנֵי יִשְׂרָאֵל וַיַּחֲנוּ בְּאֹבֹת׃ 

The people came to Moses and said, “We sinned by speaking against the LORD and against you. Intercede with the LORD to take away the serpents from us!” And Moses interceded for the people.

Then the LORD said to Moses, “Make a seraph figure and mount it on a standard. And if anyone who is bitten looks at it, he shall recover.” 

Moses made a copper serpent and mounted it on a standard; and when anyone was bitten by a serpent, he would look at the copper serpent and recover.

The Israelites marched on and encamped at Oboth.

But you’d be wrong. In fact the episode in the Bible and the fiery snakes that cured has nothing to do with this medical symbol of healing.

“From the beginning of the 17th century, the figure of Asklepios began appearing on medical medals and calling cards. The same pattern seen in antiquity emerged: The symbol was used only in a medical context, whereas the caduceus, although used by some medical organizations, was associated with other fields, especially commerce, communications, chemistry, and pharmacy”

— Robert A. Wilcox. Emma M. Whitham. The Symbol of Modern Medicine: Why One Snake Is More Than Two. Ann Intern Med. 2003;138:673-677.

snakes that heal

Here is the cover of Fred Rosner's book; notice what looks like two snakes wrapped around a winged pole.  Compare that image with the insignia of the US Army Medical Corps below.

The image you see is the caduceus, the rod carried by the Greek god Hermes (known as Mercury when he was in Rome). But in fact this double-snake flying-rod has nothing to do with healing, and is erroneously -though very widely- used as a medical emblem.  As an article in the Annals of Internal Medicine points out, the adoption of the double-snaked caduceus of Hermes - at least in the US - is likely due to its having been used as a watermark by the prolific medical publisher John Churchill.   

The correct mythological association is with the Staff  of Asklepios, the ancient Greco-Roman god of medicine. The opening lines of the Hippocratic Oath clearly reveal the central role occupied by Asklepios (and his mythologic daughters, Hygieia and Panakeia,) in the hearts and minds of the ancients: “I swear by Apollo Physician and Asklepios and Hygieia and Panakeia and all the gods and goddesses, making them my witnesses, that I will fulfill according to my ability and judgement this oath and this covenant . . .”

In one legend, a snake placed some herbs into the mouth of another serpent that Asklepios had killed, and the dead snake was restored to life.  As a mark of respect, Asklepios adopted as his emblem a snake coiled around his staff.  While the US Army Medical Corps uses the caducues as its badge, on its regimental flag the US Army Medical Command uses the more appropriate single snaked staff. Oh, and a rooster.  

U.S. Army Medical Command Regimental Flag. Don't ask about the rooster...

Fortunately, the Israel Defense Forces clearly know a caduceus from an Asklepios. They adopted the correct Greco-Roman mythological symbol for the medical unit of the first Jewish army in 2,000 years.

The Greeks may have had their tradition, but we have ours. And as the Midrash notes, in ours, it is never the snake that heals.

“עשה לך שרף ושים אותו על נס, והיה כל הנשוך וראה אותו וחי. וכי נחש ממית או נחש מחיה? אלא בזמן שישראל מסתכלין כלפי מעלה ומשעבדין את לבם לאביהן שבשמים היו מתרפאים, ואם לאו היו נימוקים...

”Make a fiery snake and place it on a pole, and it will be that anyone who is bitten will look at it and live” [Numbers 21:8] But is a snake the source of life and death? Rather, the verse means that when Israel looked up and submitted their heart to their Father in Heaven, they were healed, but if they did not do so, they perished.”

— Mishnah Rosh Hashanah 3:8

[An encore post from here.]

Pesachim 41 ~ The Hot Springs of Tiberius

The New York Times, Nov 10,2020

Last month, a group of hikers in America’s beautiful Yellowstone National Park were banned from the park for two years, sentenced to two years’ probation, and fined between $500 and $1,200. Their crime? Cooking chickens in the park’s famous hot springs. As reported in The New York Times, it is illegal to go off the boardwalk or designated trails and to touch or throw objects into hot springs or other hydrothermal features at the park. It’s also dangerous. “The water in the park’s hydrothermal systems can exceed 400 degrees Fahrenheit and can cause severe or fatal burns,” said a park spokeswoman. But had the hikers done this on a Saturday, at least they would not have broken any laws that prohibit cooking on Shabbat. We learn this in today’s page of Talmud.

פסחים מא, א

אָמַר רַב חִסְדָּא: הַמְבַשֵּׁל בְּחַמֵּי טְבֶרְיָא בְּשַׁבָּת — פָּטוּר. פֶּסַח שֶׁבִּשְּׁלוֹ בְּחַמֵּי טְבֶרְיָא — חַיָּיב

Rav Chisda said: One who cooks food in the hot springs of Tiberias on Shabbat is exempt. One violates the Shabbat prohibition of cooking only if he uses a fire. In the case of a Paschal lamb that was cooked, i.e., boiled, in the hot springs of Tiberius, one is liable for boiling the offering [for it may only be eaten roasted over a fire].

Rav Chisda’s ruling is based on the simple premise that the kind of cooking that is forbidden on Shabbat is that which involves fire. If you cook by another means, like for example, the sun’s heat, then there is no Sabbath violation. And according to the sages of the Talmud, the hot springs of Tiberius (and Yellowstone too, I presume) are heated by the sun. Hence there is no prohibition against cooking in hot springs on Shabbat. But before gently lowering your chicken into the waters, check with a park ranger first.

How The Sun heats the Hot Springs

How does the sun manage to heat up the waters of the hot springs on Tiberius? Here is Rashi’s explanation:

רשי ד׳ה שלנו פסחים מב,א

בימות הגשמים חמה מהלכת בשיפולו של רקיע לפיכך כל העולם צונן ומעיינות חמין

…During the winter the sun is low in the sky. This is the reason that it gets cold, but the springs are warm…

The idea is this: as the sun travels low in the sky during the winter it cannot provide warmth. But it manages to heat up the springs because of its path at night, when it travels under the earth. This is made explicit in a famous passage later in this tractate:

פסחים צד,ב

חַכְמֵי יִשְׂרָאֵל אוֹמְרִים בַּיּוֹם חַמָּה מְהַלֶּכֶת לְמַטָּה מִן הָרָקִיעַ וּבַלַּיְלָה לְמַעְלָה מִן הָרָקִיעַ וְחַכְמֵי אוּמּוֹת הָעוֹלָם אוֹמְרִים בַּיּוֹם חַמָּה מְהַלֶּכֶת לְמַטָּה מִן הָרָקִיעַ וּבַלַּיְלָה לְמַטָּה מִן הַקַּרְקַע אָמַר רַבִּי וְנִרְאִין דִּבְרֵיהֶן מִדְּבָרֵינוּ שֶׁבַּיּוֹם מַעֲיָנוֹת צוֹנְנִין וּבַלַּיְלָה רוֹתְחִין 

The Jewish Sages say that during the day the sun travels beneath the firmament and is therefore visible, and at night it travels above the firmament. And the sages of the nations of the world say that during the day the sun travels beneath the firmament, and at night it travels beneath the earth and around to the other side of the world. Rabbi Yehuda HaNasi said: And the statement of the sages of the nations of the world appears to be more accurate than our statement. A proof to this is that during the day, springs that originate deep in the ground are cold, and during the night they are hot compared to the air temperature [which supports the theory that these springs are warmed by the sun as it travels beneath the earth].

(To read more Talmudology on the orbit of the sun click here.)

Why do lakes seem warm at night?

According to the great editor of the Mishnah Rabbi Yehuda HaNasi, at night the water in lakes feels warmer than the surrounding cool air. His explanation (which was not really his, but that of the “sages of the nations of the world”) was that the sun was actually warming the water as it passed underneath on its nightly path under the flat earth, much like your stove heats a pot of water from the underneath.

What is really going on

The phenomena that Rabbi Yehudah HaNasi described, in which a body of water feels warmer at night (when compared with the surrounding cool night air) than it did during the day, is due to a property we now call specific heat or heat capacity. Because the heat capacity of water is about four times that of air, water takes longer to heat up but also longer to cool down than does the surrounding air; as a result, when compared to the cooler night air, the water feels comparatively warmer at night than it did during the day. This is also the reason that the weather in coastal areas is generally milder than areas more inland; the ocean traps the sun’s heat and slowly releases it, preventing large fluctuations in temperature. All this was not known to Rabbi Yehudah HaNasi (or anybody else back then) and he came up with another explanation entirely.

Don’t touch that water!

The theory that the sun slips underneath the earth each night and warms up spring water has halakhic ramifications to this day. Since spring water (and not just hot spring water) was thought to be warm, it could not be used in the process of baking matzah for Passover. Its warmth would speed up the process of leavening and turn the matztot into forbidden bread. And so we read in tomorrow’s page of Talmud (Pesachim 42a)

אָמַר רַב יְהוּדָה: אִשָּׁה לֹא תָּלוּשׁ אֶלָּא בְּמַיִם שֶׁלָּנוּ

Rav Yehuda said: A woman may knead matza dough only with water that rested, i.e., water that was left indoors overnight to cool.

If water is added to dough immediately after it was drawn from a well or spring, when it is still lukewarm, the dough will leaven at a faster rate. The German Rabbi Jacob Moellin (1365–1427) ruled that water used to make matzot must be drawn immediately after sunset, because after this time the sun warms the water as it passes beneath the earth (Sefer Maharil 6b). This opinion was codified in the Shulhan Arukh, the Code of Jewish Law written by Joseph Caro in the sixteenth century.

שולחן ארוך אורח חיים 455:1

אין לשין אלא במים שלנו בין שהם מי בורות ומעיינות בין שהם מי נהרות ושואבים אותם מבעוד יום (סמוך לבין השמשות) (ד"ע והגהות מיימוני פ"ה) או בין השמשות ואין לשין בהן עד שיעבור הלילה כולה ויכולים לשאוב יום אחד לימים הרבה ואם הזמן חם יניחם במרתף שהוא קר ואם הזמן קר יניחם באויר כי המרתף הוא חם וצריך להשכים ולהכניסם לבית קודם שיזרח השמש ואפילו ביום המעונן

One may only knead dough with water that has “rested,” regardless of whether the water comes from a well, a spring or a river. The water must be drawn during the day, and may not be used until the entire night has passed…

What happens to jewish law when our understanding of the natural world changes?

We now know that the sun does not travel under a flat earth at night, and the springs of Tiberius are not heated by the sun as it does so. As the National Park Service helpfully notes,

…hot springs are heated by geothermal heat—heat from the Earth's interior. In volcanic areas, water may come into contact with very hot rock heated by magma… In non-volcanic areas, the temperature of rocks within the Earth also increases with depth—this temperature increase is known as the Geothermal Gradient. If water percolates deeply enough into the crust, it comes into contact with hot rocks and can circulate to the surface to form hot springs.

Hanokh Ehrentreu, Sheyorei Haminhah, Haifa 1972, p 268.

If in fact hot springs are not heated by the sun but by volcanic heat, then, and by the Talmud’s own logic, cooking in their waters on Shabbat may actually be forbidden, since the water was directly or indirectly heated by fire.*

But that’s not how traditional Jewish law works. Once a rule is on the books, it pretty much stays there, regardless of any change in the factual basis on which it may have been constructed. With the later acceptance of the Copernican model the law about drawn water remained unchanged. For example, Rabbi Hanokh Ehrentreu (1854–1927), who served as the head of the rabbinic court (Bet Din) in Munich, wrote that “today there is no one who can question [the truth of the heliocentric model] for it is beyond any doubt.” Nevertheless, Rabbi Ehrentreu (whose grandson and namesake was the head of the London rabbinic court until his retirement in 2007) wrote that the laws about the water used to make matzot remained in effect, since “we do not know all the reasons [for the law] and we must follow the rulings of all [who write on this question] whenever possible.”

(*SIDE BAR: Alert Talmudology reader and retired chemistry professor Steven Lee notes that volcanic heat might not in fact be “fire” since fire requires oxidation, and there is no oxygen deep underground. “The rocks are merely hot.” He has a point.)

Not the sun, but the fires of Hell

Although the talmudic suggestion that the hot springs of Tiberius are heated by the sun is not correct, it should be pointed out that there is another talmudic theory, and this one comes a lot closer to the geological truth. First some background. The villagers of Tiberius had once hooked up an ingenious geothermal system by which cold water running through a pipe would be warmed by the hot springs. This plumbing incurred rabbinic displeasure, as described in a Mishnah:

שבת לח,ב

מַעֲשֶׂה שֶׁעָשׂוּ אַנְשֵׁי טְבֶרְיָא וְהֵבִיאוּ סִילוֹן שֶׁל צוֹנֵן לְתוֹךְ אַמָּה שֶׁל חַמִּין. אָמְרוּ לָהֶם חֲכָמִים: אִם בְּשַׁבָּת — כְּחַמִּין שֶׁהוּחַמּוּ בְּשַׁבָּת, וַאֲסוּרִין בִּרְחִיצָה וּבִשְׁתִיָּהּ. אִם בְּיוֹם טוֹב — כְּחַמִּין שֶׁהוּחַמּוּ בְּיוֹם טוֹב, וַאֲסוּרִין בִּרְחִיצָה, וּמוּתָּרִין בִּשְׁתִיָּה

The people of the city of Tiberius ran a cold-water pipe through a canal of hot water from the Tiberius hot springs. [They thought that by doing so, they could heat the cold potable water on Shabbat.] The Rabbis said to them: If the water passed through on Shabbat, its legal status is like that of hot water that was heated on Shabbat, and the water is prohibited both for bathing and for drinking. And if the water passed through on a Festival, then it is prohibited for bathing but permitted for drinking. On Festivals, one is even permitted to boil water on actual fire for the purposes of eating and drinking.

But why would such a geothermal system be forbidden as a form of cooking? We have already established that talmudic cooking requires a fire, and that the water are heated by the sun! Not so, explained Rabbi Yossi (on Shabbat 39a):

וְהָכִי קָאָמְרִי לֵיהּ רַבָּנַן לְרַבִּי יוֹסֵי הָא מַעֲשֶׂה דְּאַנְשֵׁי טְבֶרְיָא דְּתוֹלְדוֹת חַמָּה הוּא וְאָסְרִי לְהוּ רַבָּנַן אֲמַר לְהוּ הַהוּא תּוֹלְדוֹת אוּר הוּא דְּחָלְפִי אַפִּיתְחָא דְגֵיהִנָּם

Rabbi Yossi said to them: That is not so. That incident involved derivatives of fire, as the hot springs of Tiberius are hot because they pass over the entrance to Hell. They are heated by hellfire, which is a bona fide underground fire. That is not the case with derivatives of the sun, which are not heated by fire at all.

According to Rabbi Yossi the hot springs of Tiberius are an exception to the general rule (that all hot springs are heated by the sun passing underneath them) because they are located “over the entrance to Hell.” As a result, on Shabbat these waters may not used to heat water or to cook chicken. And of course Rabbi Yossi was correct in all but one detail. As any geologist today knows full well, all hot springs, and not just those that bubble up in Tiberius, are heated by fires of Hell. We just call those hellish fires by a different name. Volcanos.

2020 End of the Year Talmudology Numbers

It’s hard to believe that just a year ago, Talmudology was celebrating the completion of the Daf Yomi cycle in Jerusalem. What has happened in the world over the the intervening twelve months has been awful. But as the promise of vaccination begins to be realized, let’s spend a moment to appreciate what a bumper year for Talmudology it has been. Last year we had almost 30,000 unique visitors and 55,000 page views. This year we almost doubled that. There were 57,000 unique visitors and over 105,000 page views. Wow.

The Most Popular Posts of 2020

Here are the ten most popular posts of 2020, together with those of 2019 for comparison.

	2020 - This Year's Top Ten Posts	2019 - Last Year's Top Ten Posts
1	Avodah Zarah 28b ~ Ear Candling. On a silly way to clean your ears.	Bava Basra 126b ~ The Healing Power of Saliva. Saliva, wound healing, and the magic of a firstborn’s spit.
2	Bava Basra 126b ~ The Healing Power of Saliva. Saliva, wound healing, and the magic of firstborn spit	Chullin 22b ~ Yellow Pigeons, Folk Medicine and Hepatitis. Why pigeons are still used to cure hepatitis
3	Kiddushin 82a ~ The Best Doctors Go to Hell. Doctors were at best useless, and at their worst, agents of death. To hell with them	Avodah Zarah 28b ~ Ear Candling. On a silly way to clean your ears.
4	Kiddushin 30a ~ How Many Letters are in a Sefer Torah? 304, 801. Or 304, 805. And why the rabbis miscounted	Kiddushin 29a ~ Swimming and Drowning. The Jewish requirement to teach a child to swim.
5	Kiddushin 29a ~ Swimming and Drowning. The Jewish requirement to teach a child to swim.	Avodah Zarah 39a ~ Do Swordfish have Scales? Actually they do. So they are kosher.
6	Bechorot 8a ~ Rashi on Mermaids NEW Mermaids in rabbinic (and Greek) literature. And a sighting by Christopher Columbus	Bava Basra 25b ~ The Sun's Orbit Around the Earth. The rabbis of the Talmud vs. Copernicus.
7	Berachot 50a ~ "The Three Who Ate" - on Yom Kippur NEW David Frischmann wrote a story about the rabbi who made Kiddish on Yom Kippur. But was it true?	Kiddushin 30a ~ How Many Letters are in a Sefer Torah? 304, 801. Or 304, 805. And why the rabbis miscounted.
8	Bechorot 16a ~ A Flat Earth, The Eye, and the Sky NEW The geocentric universe is modeled by the structure of an eye.	Kiddushin 82a ~ The Best Doctors Go to Hell. Doctors were at best useless, and at their worst, agents of death. To hell with them.
9	Berachot 2 ~ How Many Words Are In the Babylonian Talmud? NEW 1.8 million, give or take	Bava Basra 27b ~ The Roots of a Palm Tree. How the United Nations supported Abayye’s botanical opinions.
10	Niddah 13 ~ Onanism, Self-Pollution and Potential People NEW The Talmud viewed sperm as potential people. It’s a viewpoint very removed from our own.	Ketuvot 36a ~ The Aylonit Syndrome and Turner's Syndrome. How genetics sheds light on a Talmudic category.

Where are the Talmudology readers FROM?

Here are the top five Talmudology reading countries:

1. USA - 61% (46,000 visitors)

2. Israel 12% (9,000 visitors)

3. United Kingdom 5% (4,200 visitors)

4. Canada 3% (3,000 visitors)

5. Australia 2% (1,600 visitors)

And there are plenty of readers from unexpected places too. Over 700 people enjoyed Talmudology in India, 90 were in Saudi Arabia when they read about the Talmud and 55 were in Iran. We should also welcome the 114 readers from the United Arab Emirates, a country now officially at peace with Israel. We value your readership, and don’t worry, we cannot identify any of you in more detail, even if we wanted to.

help talmudology reach its 1,000th subscriber

We are very close to welcoming our 1,000th email subscriber. With your help we can reach this goal. Here is a little incentive. If you already subscribe, please encourage a friend to do so. When they have signed up, let me know. The 1,000th subscriber, together with the existing subscriber who sent them, will each receive a signed copy of New Heavens and A New Earth, which is otherwise available on Amazon for the crazy price of $110. Already own a copy? Then instead you can get a signed copy of Influenza: The Hundred Year Hunt to Cure the Deadliest Disease in History.

Sign up here for email alerts, and follow us on Twitter (@Talmudology) as we continue to study science, medicine and the Talmud.

תכלה שנה וקללותיה, תחל שנה וברכותיה

The Year and its Curses have Come to an End

May the Next Year and its Blessings Begin*

*See Talmud Bavli Megillah 31b

Pesachim 35a ~ The Chemistry of Chametz

Today we will discuss the chemistry of chametz, prompted by this passage in tomorrow’s page of Talmud:

פסחים לה, א

אמר ריש לקיש וכן תנא דבי ר' ישמעאל וכן תנא דבי ר' אליעזר בן יעקב אמר קרא (דברים טז, ג) לא תאכל עליו חמץ שבעת ימים תאכל עליו מצות לחם עוני דברים הבאים לידי חימוץ אדם יוצא בהן ידי חובתו בפסח יצאו אלו שאין באין לידי חימוץ אלא לידי סירחון

How do we know that matzah must be made from one of five species of grain [wheat, barley, oats spelt and rye]?  Reish Lakish said, and likewise a Sage of the school of Rabbi Yishmael taught, and likewise a Sage of the school of Rabbi Eliezer ben Ya’akov taught, that the verse states: “You shall eat no leavened bread with it; seven days you shall eat with it matzah, the bread of affliction” (Deuteronomy 16:3). This verse indicates that only with regard to substances that will come to a state of leavening does a person fulfill his obligation to eat matzah by eating them on Passover, provided that he prevents them from becoming leavened. This serves to exclude these foods, i.e., rice, millet, and similar grains, which, even if flour is prepared from them and water is added to their flour, do not come to a state of leavening but to a state of decay [sirḥon].

The important question we need to answer here is whether there is something fundamentally different about rice when compared to the five grain species that can become chametz. And is there any scientific support to the claim that rice spoils sooner than it ferments?

The Chemistry of bread making

To get at the answers we need to remind ourselves how plants make and consume starch. They take carbon dioxide from the atmosphere and water from the soil, and using the energy contained in sunlight (and the magic of chlorophyll) convert the two into a large sugar molecule we call starch. Plants use this starch to store and provide them with energy.

If you grind up wheat (or many other species of grain) you make flour which contains loads of starch. In addition to starch, flour contains proteins and enzymes which become important when the flour is mixed with water. Without going down a rabbit-hole of detail, here in general is what happens. First, an enzyme called beta-amylase breaks the large starch molecule down into a smaller molecule called maltose which is made up of two molecules of glucose. Another enzyme, maltase, breaks down each molecule of maltose into two molecules of glucose which is then broken down further to provide the plant with energy. Here is what it looks like:

From Lloyd, James R and Kötting, Oliver (July 2016) Starch Biosynthesis and Degradation in Plants. John Wiley & Sons, Ltd: Chichester.

If you add some yeast into that mix, a chemical reaction called fermentation occurs. Yeast, which is a fungus, consumes glucose and turns it into carbon dioxide and ethanol, which is an alcohol.

As the flour and water and yeast all mix together, two proteins in the flour called gliadin and glutenin (which are glutens) give the dough mixture its characteristic body, which strengthens the more it is mixed. The dough traps the carbon dioxide that is given off by the yeast cells, which causes the bread to rise. And that gives us the leavened bread we call chametz.

Of course when matzah is made, we do not add yeast to the dough. But there are yeast particles in the air and these will inevitably land on the dough where they will act in the same way, consuming glucose and creating carbon dioxide and alcohol. This process is much slower than when yeast is added when bread is made, but the plain dough will rise a little as a result.

The differences between grains and rice

Resh Lakish (together with those sages of the schools of Rabbi Yishmael and Rabbi Eliezer ben Ya’akov) claim that unlike grains, rice does not ferment when water is added to it. Instead it spoils. That’s why it may be eaten on Passover (unless of course you are an Ashkenazi Jew, in which case you still can’t eat it, but for another reason we’re not going to get into). Is this in fact the case?

I know next to nothing about plant biology. But Dr Angus Murphy does. He is Professor and Chair of the Department of Plant Science at the University of Maryland, and wrote the textbook on plant physiology. Dr. Murphy was kind enough to have a long chat with me over the phone and he agreed with the suggestion that grains and rice do very different things when mixed with water. The wheat seed is surrounded by the endosperm, which is itself covered by the aluerone layer. This aleurone is rich in amylase which as you recall is needed to breakdown starch into glucose (which is eaten by yeast which releases carbon dioxide and alcohol which causes the dough to rise…) However (most species of) rice do not contain this aleurone layer. So they have very little amylase, which means that it takes them a much longer time to convert starch into glucose. In fact it takes so long that by the time there is enough yeast in the dough for it to start to rise, bacteria in the air will have colonized the mixture and started breaking down the proteins in the dough. And that protein breakdown is what makes the mixture spoil, and which is what the Talmud calls סירחון. To conclude, Professor Murphy thought that the Talmud’s description of the difference between grain and rice was firmly based in plant biology.

The fine print and the final verdict

Distribution of variou types of amylases in rice grains. (Beta-Amylase activity was expressed in terms of maltose mg liberated in 3 min at 30°C by 1 g of ground rice samples.) From Ryu Shinke, Hiroshi Nishira & Narataro Mugibayashi. Types of Amylases in Rice Grains. Agricultural and Biological Chemistry 1973; 37:10, 2437-2438

Of course things are a little more complicated than that. (They always are.) Different kinds of wheat flour contain different amounts of amylase. Fine bleached white flour contains less amylase than say whole wheat flour, because the aleurone layer in whole wheat flour has not been broken down. Similarly, different species of rice contain different amounts of amylase, so that while standard white rice has very little, brown rice has considerably more. During talmudic times, the wheat flour would have been far less processed than any of the flour we would use today. As a result it would contain more amylase, and would have risen faster than would today’s supermarket flour..

But as a rule of thumb, the Talmud is, biochemically speaking, spot on. When mixed with water, the five species of grain from which matzah may be made do undergo fermentation even without the addition of yeast, while rice will spoil long before the fermentation process becomes noticeable.