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Joseph Weinstein





Red Heifer: A Soap Ritual



APA e-journal

Joseph Weinstein





Red Heifer: A Soap Ritual






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Red Heifer: A Soap Ritual

After contact with a corpse, a person must be sprinkled with a liquid mixture containing the ashes of a red heifer, together with cedar and ezov, alkaline plants that, when burnt, function as the key ingredients in a detergent.


Red Heifer: A Soap Ritual

Sacrifice of the Red Heifer (adapted), anonymous, 18th c. Rijksmuseum

The Torah prescribes an elaborate form of ritual purification for a person or object that has become impure through contact with a dead body. It begins with the sacrifice of a פָרָה אֲדֻמָּה “red cow”[1] outside the camp (Num 19:2–3). The priest sprinkles the blood of the animal seven times towards the Tent of Meeting, after which the animal is burned:

במדבר יט:ה וְשָׂרַף אֶת הַפָּרָה לְעֵינָיו אֶת עֹרָהּ וְאֶת בְּשָׂרָהּ וְאֶת דָּמָהּ עַל פִּרְשָׁהּ יִשְׂרֹף.
Num 19:5 The cow shall be burned in his sight—its hide, flesh, and blood shall be burned, its dung included.[2]

The priest throws several additional materials into the fire (v. 6, more on this below), and then the ashes are collected:

במדבר יט:ט וְאָסַף אִישׁ טָהוֹר אֵת אֵפֶר הַפָּרָה וְהִנִּיחַ מִחוּץ לַמַּחֲנֶה בְּמָקוֹם טָהוֹר וְהָיְתָה לַעֲדַת בְּנֵי יִשְׂרָאֵל לְמִשְׁמֶרֶת לְמֵי נִדָּה חַטָּאת הִוא.
Num 19:9 A man who is clean shall gather up the ashes of the cow and deposit them outside the camp in a clean place, to be kept for water of lustration for the Israelite community. It is a chatat (“sin” or “purification” offering).

This ash is mixed with water and sprinkled on a person who contacts a corpse:

במדבר יט:יז וְלָקְחוּ לַטָּמֵא מֵעֲפַר שְׂרֵפַת הַחַטָּאת וְנָתַן עָלָיו מַיִם חַיִּים אֶל כֶּלִי. יט:יח וְלָקַח אֵזוֹב וְטָבַל בַּמַּיִם אִישׁ טָהוֹר וְהִזָּה עַל הָאֹהֶל וְעַל כָּל הַכֵּלִים וְעַל הַנְּפָשׁוֹת אֲשֶׁר הָיוּ שָׁם וְעַל הַנֹּגֵעַ בַּעֶצֶם אוֹ בֶחָלָל אוֹ בַמֵּת אוֹ בַקָּבֶר.
Num 19:17 Some of the ashes from the fire of cleansing shall be taken for the unclean person, and fresh water shall be added to them in a vessel. 19:18 A person who is clean shall take hyssop, dip it in the water, and sprinkle on the tent and on all the vessels and people who were there, or on him who touched the bones or the person who was killed or died naturally or the grave.

Only after being sprinkled twice with this solution—on the third and seventh days after contamination—can the person bathe and be declared ritually clean (v. 19).

A Decree

The Torah does not explain the significance of the ritual’s details. Rabbinic literature regards the Red Heifer ritual as the quintessential example of a chukkah (חקה)—a divinely-ordained law that has no obvious humanely-discernable reason.[3] For example, the Pesikta deRav Kahana[4] writes:

אלא א[מר] הקב"ה: חוקה חקקתי וגזירה גזרתי ואין את רשיי לעבור על גזירתי, זאת חוקת התורה אשר צוה י"י לאמר.
The Holy One, blessed be He, said (to Moses): I have ordained a chukkah and decreed a decree, and you are not free to violate my decrees: “This is the chukkah of the Torah which the Lord commanded….” (Parah ʾadummah, piska 4:1)

In the same Midrash, Rabbi Yochanan b. Zakkai tells his students:

חייכם לא המת מטמא ולא המים מטהרים אלא גזירתו של הקב"ה הוא.
“By your lives! Neither the dead body (intrinsically) causes impurity nor does the water (intrinsically) purify, but rather it is a decree of the Holy One, Blessed be He.”[5]

Several details in the Red Heifer text, however, suggest a practical explanation for its requirements: this symbolic cleansing ritual may be built on a physical cleansing procedure utilizing an ancient formula for making soap.[6]

Soapmaking Basics

The principal ingredients required in soap are a fat or oil, from either plant or animal sources,[7] and an alkali (usually sodium or potassium lye). An alkali can be prepared by burning plants containing sodium and potassium and mixing the ashes with water. The ash contains lime (calcium carbonate), soda ash (sodium carbonate and/or sodium bicarbonate), potash (potassium carbonate), and various other minerals.[8] The soda ash and potash dissolve in the water, forming an alkaline solution and leaving the less-soluble lime behind. Under proper conditions, the heat and lime convert the soda ash and potash to the corresponding oxides and hydroxides, creating true lye.[9] Different plants vary significantly in the chemical composition of their ash, and hence their suitability for producing such solutions.[10]

The solution can be used as a cleansing agent, much as baking soda (sodium bicarbonate) and water are used today. When combined with fat or oil, however, it will produce a crude soap. This is the type of soap probably used in antiquity.

Soap and Alkalis in the Ancient Near East

The use of alkalis such as potash, soda ash, and baking soda to make cleansing agents or soaps was known in the ancient Near East.[11] A Sumerian tablet describes successive steps in cleansing as washing in water, then purification with soda, and finally anointing with oil:

With water I bathed myself. With soda I cleansed myself. With soda from a shiny basin I purified myself. With pure oil from the basin I beautified myself.[12]

One of the Cylinders of Gudea (Sumeria, third millennium B.C.E.) specifies water, alkali, and oil as the ingredients for cleaning:

So that he makes pure with water, so that he cleanses with potash,[13] and so that he intermixes the pure oil with potash.[14]

The Egyptian Ebers medical papyrus (ca. 1534 B.C.E.) gives numerous recipes for the manufacture of soaps or salves from alkalis boiled together with fats and oils.[15] The slightly later Berlin medical papyrus (Egypt, ca. 1350 B.C.E.) likewise gives a recipe for the making of soaps or salves from natron and tallow.[16]

An Akkadian tablet from the first millennium B.C.E. gives a recipe that is made by combining alkalis obtained from Salicornia and mastakal with various oils, fat of a cow, and other substances.[17]

In the Bible, neter[18] and borit are both mentioned as cleansing agents and are probably some combination of potash, soda ash, and other salts:[19]

ירמיה ב:כב כִּי אִם תְּכַבְּסִי בַּנֶּתֶר וְתַרְבִּי לָךְ בֹּרִית נִכְתָּם עֲוֹנֵךְ לְפָנַי נְאֻם אֲדֹנָי יְ־הוִה.
Jer 2:22 Though you wash with natron (neter) and use much lye (borit), your guilt is ingrained before Me—declares the Lord YHWH.

Missing or Irrelevant Details in the Recipes

Unlike modern recipes, which typically provide a complete list of ingredients and process steps, most of the extant ancient recipes, whether for food, medicine, or soap, are incomplete and unclear. Indeed, some of the soap recipes would be more accurately described as incantations that invoke the cleansing properties of the materials used in manufacturing soap, rather than as actual formulas for that purpose. For example, an Akkadian anti-witchcraft incantation known as maqlû (first millennium B.C.E.) invokes the power of several plants as part of a symbolic cleansing of the speaker:

May the tamarisk that is copious of crown clear me, may the date palm that withstands all winds release me, may the mastakal that fills the earth cleanse me, may the cone of a pine tree release me.[20]

Like mastakal, tamarisk occurs as a cleansing agent in other texts. Both plants may have been sources of alkali.[21]

Several factors complicate our understanding of ancient soap making:

  • Since the authors of these recipes lacked modern knowledge of chemistry, they did not always understand which ingredients and steps in their procedures were necessary to produce an effective cleanser or soap.
  • Recipes may be missing critical steps or ingredients, or they may include irrelevant details—ingredients and procedures that are not chemically necessary for producing soap.
  • Very few recipes specify the quantities of the substances used, nor do they contain detailed instructions regarding how the substances are to be prepared.
  • Very few, if any, explicitly label their product as “soap”; it is recognizable as such only from its ingredients and uses.
  • Not all of the ingredients in these texts can be identified today, and the roles of the ingredients in the formula are not always clear.

For example, an Akkadian text from the 1st millennium B.C.E. gives a prescription for washing using a substance containing turmeric, an alkali, the fat of a crane, and several other ingredients:

A vessel is to be filled with water from a pool, untouched by hand (washing), and tamarisk, mastakal (soapwort),… [a type of reed], Salicornia alkali, and “mixed” beer put therein, and then a ring of ṣariru-gold; the man [is] to be given pure water to drink, and then the water thus prepared is to be poured over him: then turmeric root is to be pulled up, pure salt and pure alkali pounded, fat of a crane brought from the mountains added to this, and the patient’s body rubbed seven times with it.[22]

The admixture of ritualistic/magical components, the lack of precise measurements, and the incomplete instructions, are obvious.

To employ such recipes successfully, the ritual practitioners must have possessed additional, traditional, practical knowledge, which they did not commit to writing and may have deliberately kept secret.

Lye from the Red Heifer

Like these ancient soap recipes, the Red Heifer ritual may also have irrelevant or missing details. Burning the red heifer, for example, does not contribute chemically to the soap-making. Like all bone ash, the animal’s ashes would have consisted primarily of calcium phosphates.[23] These are insoluble in water, and hence would have neither aided nor hindered soap-making. The large quantities of wood or other plants needed as fuel for the fire, however, would have produced an alkaline solution when mixed with water—an impure lye—that would have been potentially useful for cleaning purposes.

Many kinds of plants will produce the necessary ash, but Numbers requires that several specific ingredients be thrown into the fire:

במדבר יט:ה וְשָׂרַף אֶת הַפָּרָה לְעֵינָיו אֶת עֹרָהּ וְאֶת בְּשָׂרָהּ וְאֶת דָּמָהּ עַל פִּרְשָׁהּ יִשְׂרֹף. יט:ו וְלָקַח הַכֹּהֵן עֵץ אֶרֶז וְאֵזוֹב וּשְׁנִי תוֹלָעַת וְהִשְׁלִיךְ אֶל תּוֹךְ שְׂרֵפַת הַפָּרָה.
Num 19:5 The cow shall be burned in his sight—its hide, flesh, and blood shall be burned, its dung included— 19:6 and the priest shall take ʾerez, ʾezov, and sheni tolaꜥat, and throw them into the fire consuming the cow.

What were ʾerez, ʾezov, and sheni tolaꜥat, and how would their inclusion in the fire affect the resulting ash or the lye solution made from it?

ʾErez (Cedar Wood)

The identification of ʾerez is clear: it is the resinous, aromatic, reddish wood of certain coniferous trees. In most biblical contexts, it refers specifically to Lebanese Cedar, Cedrus libani, an evergreen conifer that thrives in the mountains of Lebanon.[24] Since Lebanese Cedar rarely grows south of Mt. Hermon (Mt. Lebanon), it is possible that the reference in this and a few other passages is to one or another evergreen conifer also commonly known as cedar, such as certain species of juniper (Juniperus oxycedrus or Juniperus turbinata, a.k.a. Sabina phoenicia v. turbinata).[25] We know from the library of Ashurbanipal (Assyria, 7th century B.C.E.) that Juniperus oxycedrus was included in a soap-making recipe.[26]

Potassium could probably have been leached directly as lye from cedar ashes, as is the case with other softwoods.[27] However, relevant chemical analyses specific to cedar and juniper ash do not appear to be available.

The Biblical text only requires the addition of ʾerez to the fire; other types of wood may have been employed as well.[28] These may also have contributed potassium through their ashes.


The identity of ʾezov is uncertain, but references to it in this and other texts offer insight into its properties.[29] ʾEzov was both thrown into the sacrificial pyre of the Red Heifer (Num. 19:6) and employed as an applicator brush for sprinkling the ashes (Num. 19:18).

According to Tannaitic sources, large quantities of ʾezov (and, in some opinions, other plants) were heaped on the burning cow to produce copious ashes.

תוספתא פרה ד:י לעולם מרבין לה עצים. אמר ר׳ יהודה: אף כשהיו מרבים לא היו מרבים אלא חבילי אזוב שאפרן מרובה ויפה.
t. Parah 4:10 At all times do they add wood to it. Said Rabbi Judah: “Even when they would add [wood], they would add only bundles of ʾezov, whose ashes are good and abundant.”[30]

ʾEzov is closely associated with cleansing in other ritual texts (Exod 12:22, Lev 14:4–6, 14:49–51), usually as an applicator. In Psalms it is used in a metaphor related to seeking God’s forgiveness:

תהלים נא:ט תְּחַטְּאֵנִי בְאֵזוֹב וְאֶטְהָר תְּכַבְּסֵנִי וּמִשֶּׁלֶג אַלְבִּין.
Ps 51:9 Purge me with ʾezov until I am pure; wash me till I am whiter than snow.

The inclusion of ʾezov in the Red Heifer ritual thus probably also serves a real or symbolic cleansing purpose.

Scholars have attempted to identify ʾezov with several different plants. The Septuagint transliterates ʾezov as “hyssop,” based upon phonetic similarity. Later herbalists and botanists identified this “hyssop” with a Southern Mediterranean herb known today as Hyssopus officinalis. This solution is implausible, however, because the plant is not native to Israel or Egypt.[31]

Most scholars argue that ʾezov refers to Origanum syriacum (Arabic zaatar). This seems to be Saadia Gaon’s view in his Tafsir,[32] and is what Samaritans’ use in their Passover ritual.[33] This identification is not certain, however, because Origanum syriacum does not fully match descriptions of biblical ʾezov.[34] Also possible is Capparis sicula or spinosa (the Caper plant), a plant that is widespread in Israel, Sinai, and the Nile Delta.[35] Both are rich in the potassium needed for soap-making.[36]

Another possible identification is with one of the reed grasses, probably Sorghum vulgare (a.k.a. Sorghum bicolor, a grass cultivated for its grain) or Arundo donax (a tall reed or cane).[37] Reeds would be particularly appropriate for use as an applicator brush, and are among the few possibilities that would have been available in sufficient quantity to have fueled the sacrificial pyre in more than a symbolic capacity.[38] Reeds are also especially rich in potassium,[39] and hence would have been particularly suitable for soap-making. For example, the Assyrian text quoted previously included some kind of reed as one of its ingredients.

Sheni Tolaꜥat

Most translations render sheni tolaꜥat (שְׁנִי תוֹלָעַת), literally, “crimson (dye) from a worm,” as “crimson stuff,” “wool dyed red,” or something similar. The reference is most likely to kermes, a dye obtained from crushing and drying scale insects such as Kermes echinatus or Kermes vermilis.[40] These were widely used in antiquity to produce a brilliant red dye. The crimson dye would have most likely been added to the fire in powder form.

From Blood Red to Pure White

The inclusion of several red ingredients—the sheni tolaꜥat, the red cow, and its blood—none of which are chemically necessary to produce soap, suggests that the color has symbolic significance. Taking red objects, burning them, and mixing them in water would have symbolized the process of cleansing.[41] The transformation from red to clear could be understood as symbolic of moving from impure to pure. A metaphor along these lines appears in Isaiah:

ישׁעיה א:יח לְכוּ נָא וְנִוָּכְחָה יֹאמַר יְ־הוָה אִם יִהְיוּ חֲטָאֵיכֶם כַּשָּׁנִים כַּשֶּׁלֶג יַלְבִּינוּ אִם יַאְדִּימוּ כַתּוֹלָע כַּצֶּמֶר יִהְיוּ.
Isa 1:18 “Come, let us reach an understanding,” says YHWH. “Even if your sins are like crimson (shenim), they shall become white as snow; even if they are as red as a worm (tolaꜥat), they shall become as (white as) wool.”

Soap or Cleaning Solution? Depends on the Fats

Whether the Red Heifer ritual led to production of a soap or stopped with production of an alkaline cleaning solution depends upon how the animal’s חֵלֶב, referring to the fat surrounding the entrails and organs, was employed.[42] The text omits this detail.

A comparison with the chatat sacrifice of the High Priest (Lev 4:1–12) highlights the silence about chelev in the Red Heifer ritual, as the sacrifice of the Red Heifer is also described as a chatat:.


Chatat of the High Priest
(Lev 4:1–12)

Red Heifer
(Num 19:1–22)


A bull of the herd

A red cow


Entrance of the Tent of Meeting

Outside the camp


In the Tent of Meeting, sprinkled seven times front of curtain of the shrine; put on horns of incense altar; remainder poured out at base of altar of burnt offering

Sprinkled seven times toward front of the Tent of Meeting; remainder burned with cow

Chelev (fat)

Removed from the ox and burned on the altar

(no mention)


Fat burned on the altar of burnt offering

(no mention)

Rest of animal

Hide, flesh, head, legs, entrails, and dung burned at clean place outside camp

Hide, flesh, blood, and dung burned at site of sacrifice

Notably, the chatat of the High Priest requires removing the chelev from the animal and burning it on the altar, producing smoke. By contrast, the Red Heifer ritual makes no mention of what should be done with the chelev, nor does it refer to the fat indirectly by mention of the smoke that it would have produced during burning. Instead of assuming that the fat was burned with the rest of the animal, it may be that the ritual text is simply incomplete: a piece of practical knowledge on the part of the priests was not committed to writing, either inadvertently or because it was a trade secret.

As noted earlier, soap-making requires an alkali—plant ash, in this case—water, and a fat or oil. If the chelev was burned on the altar or with the cow, it would not contribute to soap making, and the formula would simply produce an alkaline cleaning solution. If, however, the fats were removed, rendered, and mixed with the ashes from the sacrificial pyre at the end of the procedure, and then mixed with water as part of the subsequent purification ritual, the result would be soap. This, then, would have been the secret of the Red Heifer ritual, shrouded in mystery for centuries: cleansing from the impurity of death needs more than just water, it requires soap.


July 3, 2022


Last Updated

April 15, 2024


View Footnotes

Dr. Joseph Weinstein is an interdisciplinary researcher with widespread interests in science, technology, ancient history, and archaeology. He holds a Bachelor’s degree in Physics from Princeton University, a Master’s in Jewish Education from Boston Hebrew College, and a Ph.D. in Physics from MIT, and  spent most of his professional career in private industry at Bolt, Beranek, and Newman (now Raytheon BBN Technologies) in Cambridge, MA. His activities in archaeology have focused on application of statistics and scientific data analysis techniques to pottery and other artifacts from the Ancient Near East. Participants in the annual SBL/AAR conference will recognize him as the person who usually organizes Shabbat meals and services.