Nullified Impurity, Decomposition, and Presumptions of Bekhorah

How mixtures retain impurity in carriage, when spoiled carcasses cease to defile, and why nursing animals are exempt from bekhorah.

Impure Substances Nullified in a Majority

The Gemara explores what happens when an impure item is outnumbered in a mixture by permissible matter. If red heifer ashes mix into ordinary stove ashes, or נבלה (carcass meat) mixes into שחוטה (ritually slaughtered meat), does the minority vanish entirely?

Rabbi Yosei bar Chanina resolves that while the mixture no longer transmits ritual defilement by מגע (touch), it defiles when carried. When a person touches the blend, one touches the majority; yet when one lifts the whole mass, one carries the entire measure of impurity.

נְבֵלָה שֶׁנִּתְעָרְבָה בִּשְׁחוּטָה אִם רֹב מִן הַשְּׁחוּטָה בְּטֵלָה הַנְּבֵלָה בַּשְּׁחוּטָה וְאֵין הַכּל מְטַמֵּא בְּמַגָּע. אֲבָל אִם נָשָׂא הַכּל נִטְמָא

When a carcass became intermingled with slaughtered meat, if the majority is from the slaughtered animal, the carcass is nullified and the mixture does not impart impurity when touched. But if one carried the entire mixture, he contracts impurity. (Mishneh Torah, Other Sources of Defilement 1:17)

Codification of Impurity by Carriage

The Rambam codifies this distinction across several categories of ritual purity. If red heifer ashes mix with oven ashes, a majority of ordinary ashes prevents contact defilement, yet carrying the blend imparts defilement.

Similarly, carcass flesh mixed into slaughtered meat defiles by carrying, but touching any piece remains pure. The Shulchan Arukh does not record these rules, as they concern Temple-era purity rather than current dietary prohibitions.

When Putrefaction Removes Ritual Impurity

The Gemara debates when decomposed carcass flesh ceases to impart ritual impurity. Bar Padda holds that severe impurity departs once meat is unfit for a גר תושב (resident alien). Rabbi Yochanan rules that impurity remains until the meat spoils beyond dog consumption.

The Gemara concludes that flesh decomposed from the start is like dust and never defiled. However, flesh that began edible loses its impurity only when a dog would refuse it.

וְרַבִּי יוֹחָנָן אָמַר: אַחַת זוֹ וְאַחַת זוֹ עַד לְכֶלֶב.

And Rabbi Yochanan says: Both this one and that one impart impurity until they are no longer fit to be eaten by a dog. (Bekhorot 23b:2)

The Threshold of Canine Consumption

The Rambam rules according to Rabbi Yochanan across all categories of animal and creeping creatures. Decomposing carcass meat remains impure until dog refusal, unless it was already rotted before death and never fit for human food.

This ruling also applies to ritually defiled food, which remains impure until it rots past canine edibility. This legal standard governs purity mechanics rather than modern kashrut.

Purchasing a Nursing Mother Animal

The Mishnah teaches that if one buys a nursing female animal from a gentile, there is no suspicion that she adopted another mother's newborn. We maintain a חזקה (presumption) that animals nurse only their own offspring, meaning she has already calved.

The Gemara establishes that the halacha strictly follows Rabban Shimon ben Gamliel in this ruling. Future male offspring born to this mother are completely exempt from bekhorah.

לקח בהמה מניקה מהעובד כוכבים אינו חושש שמא בנה של אחרת היא מניקה אלא הרי זו בחזקת שילדה

One who purchased a nursing animal from a gentile does not suspect that it is nursing the offspring of another animal; rather, it possesses the presumption of having given birth. (Shulchan Arukh, Yoreh De'ah 316:2)

Codification for Herd Mix-ups and Firstlings

The Rambam rules that even if the calf appears to belong to another species, the animal is exempt from בכורה (firstborn status) because animals only nurse their own. Maran in the Shulchan Arukh adopts this rule word for word.

Both the Rambam and Maran also rule that an owner who finds newly delivered mothers nursing mixed calves assumes each dam nurses her own, preserving the exemption. The Rema adds no dissenting ruling here.

Substances nullified by majority still defile when lifted, while natural maternal behavior establishes a halachic presumption that exempts future offspring from bekhorah.

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