Halacha

הלכה א
כָּל מַאֲכָל הַיּוֹצֵא מִמִּין מִן הַמִּינִין הָאֲסוּרִין שֶׁלּוֹקִין עַל אֲכִילָתָן הֲרֵי אוֹתוֹ הַמַּאֲכָל אָסוּר בַּאֲכִילָה מִן הַתּוֹרָה. כְּגוֹן חֲלֵב בְּהֵמָה וְחַיָּה הַטְּמֵאִים וּבֵיצֵי עוֹף וְדָג הַטְּמֵאִים שֶׁנֶּאֱמַר (ויקרא יא טז) (דברים יד טו) "וְאֵת בַּת הַיַּעֲנָה" זוֹ בֵּיצָתָהּ. וְהוּא הַדִּין לְכָל הָאָסוּר כְּיַעֲנָה וּלְכָל הַדְּבָרִים הַדּוֹמִין לְבֵיצָה:
כסף משנה
1.
Any food that is produced from forbidden species for which lashes are given for partaking of1I.e., foods that are forbidden by a negative commandment. is forbidden to be eaten according to Scriptural Law, e.g., milk from a forbidden species of domesticated animal or wild beast or the eggs of a forbidden species of birds or fish. [This is derived from Leviticus 11:16 which mentions]: "the bat of the ostrich." [Our Sages2Chullin 64b. The term literally means "the daughter of the ostrich." Our Sages, however, expanded the interpretation of the term as the Rambam explains. commented:] "This refers to its egg." The same law applies to all species that are forbidden like an ostrich and all entities [that are produce] like eggs.

הלכה ב
חֲלֵב הָאָדָם מֻתָּר בַּאֲכִילָה אַף עַל פִּי שֶׁבְּשַׂר הָאָדָם אָסוּר בַּאֲכִילָה. וּכְבָר בֵּאַרְנוּ שֶׁהוּא בַּעֲשֵׂה:
כסף משנה
2.
Human milk is permitted to be eaten,3I.e., even by an adult. Note, however, Halachah 4. although the meat of a human is forbidden to be eaten. We have already explained4Chapter 2, Halachah 3. that it is forbidden by virtue of a positive commandment.5Thus it does not contradict the general principle mentioned in the previous halachah.

הלכה ג
דְּבַשׁ דְּבוֹרִים וּדְבַשׁ צְרָעִים מֻתָּר מִפְּנֵי שֶׁאֵינוֹ מִתַּמְצִית גּוּפָן אֶלָּא כּוֹנְסִין אוֹתוֹ מִן הָעֲשָׂבִים בְּתוֹךְ פִּיהֶן וּמְקִיאִין אוֹתוֹ בַּכַּוֶּרֶת כְּדֵי שֶׁיִּמְצְאוּ אוֹתוֹ לֶאֱכל מִמֶּנּוּ בִּימוֹת הַגְּשָׁמִים:
כסף משנה
3.
Honey produced by bees and hornets6As the Maggid Mishneh mentions, there is a difference of opinion among the Sages in Bechorot 7b whether the honey of hornets is forbidden. This difference of opinion is perpetuated among the later authorities. See the Shulchan Aruch (Yoreh De'ah 81:9). is permitted. [The rationale is that] it is not a product of their bodies. Instead, it is collected in their mouths from herbs and then expelled in their hive so that they will be able to partake of it in the rainy season.

הלכה ד
אַף עַל פִּי שֶׁחֲלֵב אָדָם מֻתָּר אָסְרוּ חֲכָמִים לְגָדוֹל לִינֹק אוֹתוֹ מִן הַשָּׁדַיִם אֶלָּא חוֹלֶבֶת אִשָּׁה לְתוֹךְ הַכְּלִי וְשׁוֹתֶה. וְגָדוֹל שֶׁיָּנַק מִן הַשָּׁד כְּיוֹנֵק שֶׁרֶץ וּמַכִּין אוֹתוֹ מַכַּת מַרְדּוּת:
כסף משנה
4.
Although human milk is permitted, our Sages prohibited an adult to nurse from [a woman's] breasts. Instead, the woman should express it into a container7Or into a person's hands. She may not, however, express it into the person's mouth [the Shulchan Aruch (Yoreh De'ah 81:7)]. and the adult should partake of it. An adult who nurses from [a woman's] breast is like one who nurses from a teeming animal.8The Ra'avad and the Turei Zahav 81:9 explains that these words of censure were issued because an observer might think that the milk of a non-kosher animal is also permitted. He is given stripes for rebellious conduct.

הלכה ה
יוֹנֵק תִּינוֹק וְהוֹלֵךְ אֲפִלּוּ אַרְבַּע אוֹ חָמֵשׁ שָׁנִים. וְאִם גְּמָלוּהוּ וּפָרַשׁ שְׁלֹשָׁה יָמִים אוֹ יֶתֶר מֵחֲמַת בֻּרְיוֹ לֹא מֵחֲמַת חָלְיוֹ אֵינוֹ חוֹזֵר וְיוֹנֵק. וְהוּא שֶׁגְּמָלוּהוּ אַחַר כ''ד חֹדֶשׁ. אֲבָל בְּתוֹךְ זְמַן זֶה אֲפִלּוּ גְּמָלוּהוּ חֹדֶשׁ אוֹ שְׁנַיִם מֻתָּר לַחֲזֹר וְלִינֹק עַד סוֹף כ''ד חֹדֶשׁ:
כסף משנה
5.
An infant may continue to nurse for even four or five years. If, however, he was weaned for three days or more in a state of health and not because of sickness, he should not be allowed to nurse again.9Needless to say, if there is a danger to the child's life, he may be allowed to nurse again regardless of the amount of time for which he had been weaned [the Shulchan Aruch (Yoreh De'ah 81:7)]. [The above applies] provided he was weaned after 24 months. If he was weaned within that time, even if he was weaned for a month or two, it is permitted to have him nurse again until the conclusion of 24 months.10When an infant has never been weaned, he may continue past the 24 month limit as the Rambam states at the beginning of the halachah. If, however, he has been weaned, he is bound by this restriction [Beit Yosef (Yoreh De'ah 81)].

הלכה ו
אַף עַל פִּי שֶׁחֲלֵב בְּהֵמָה טְמֵאָה וּבֵיצֵי עוֹף טָמֵא אֲסוּרִין מִן הַתּוֹרָה אֵין לוֹקִין עֲלֵיהֶם שֶׁנֶּאֱמַר (ויקרא יא ח) (דברים יד ח) "מִבְּשָׂרָם לֹא תֹאכֵלוּ" עַל הַבָּשָׂר הוּא לוֹקֶה וְאֵינוֹ לוֹקֶה. עַל הַבֵּיצָה וְעַל הֶחָלָב. וַהֲרֵי הָאוֹכֵל אוֹתָן כְּאוֹכֵל חֲצִי שִׁעוּר שֶׁהוּא אָסוּר מִן הַתּוֹרָה וְאֵינוֹ לוֹקֶה אֲבָל מַכִּין אוֹתוֹ מַכַּת מַרְדּוּת:
כסף משנה
6.
Although the milk of a non-kosher animal and the egg of a non-kosher fowl are forbidden according to Scriptural Law, [one is] not [liable for] lashes [for partaking of them. [This is derived from Leviticus 11:8] which states: "You may not eat from their flesh." [Implied is that] one is liable for lashes for [partaking of] their flesh, but is not liable for lashes for [partaking of] their eggs and milk. One who partakes [of these substances] is like one who eats half the minimum measure [of a forbidden substance]. This is forbidden according to Scriptural Law, but one is not liable for lashes. Instead, he receives stripes for rebellious conduct.11See Chapter 4, Halachah 16, Hilchot Shivitat Esor 2:3, et al.

הלכה ז
יֵרָאֶה לִי שֶׁהָאוֹכֵל בֵּיצֵי דָּגִים טְמֵאִים הַנִּמְצָאִים בִּמְעֵיהֶם כְּאוֹכֵל קִרְבֵי דָּגִים טְמֵאִים וְלוֹקֶה מִן הַתּוֹרָה. וְכֵן בֵּיצֵי הָעוֹף הַטָּמֵא הַתְּלוּיוֹת בְּאֶשְׁכּוֹל שֶׁעֲדַיִן לֹא פָּרְשׁוּ וְנִגְמְרוּ. הָאוֹכֵל אוֹתָן לוֹקֶה כְּאוֹכֵל בְּנֵי מֵעַיִם שֶׁלָּהֶן:
כסף משנה
7.
It appears to me that eating the eggs of non-kosher species of fish that are found in their bellies is comparable to eating the insides of the forbidden fish themselves12For they are part of the fish's body and are not separated by a shell. and one is liable for lashes according to Scriptural Law. Similarly, when a person partakes of the eggs of a non-kosher fowl that are hanging in a cluster without being separated from the mother's body or completed, he is liable for lashes as if he ate the insides of [the fowl itself].13For this instance as well, the eggs are not a distinct entity, but instead are considered part of the fowl's body. The Maggid Mishneh brings proof of this concept from Chapter 9, Halachot 4-5, which states that it is forbidden to eat such eggs together with milk and from Hilchot Sha'ar Avot HaTumah 3:10 which states that they convey ritual impurity like the meat of the fowl itself.

הלכה ח
בֵּיצַת עוֹף טָמֵא שֶׁהִתְחִיל הָאֶפְרוֹחַ לְהִתְרַקֵּם בָּהּ וַאֲכָלוֹ לוֹקֶה מִשּׁוּם אוֹכֵל שֶׁרֶץ הָעוֹף. אֲבָל בֵּיצַת הָעוֹף טָהוֹר שֶׁהִתְחִיל הָאֶפְרוֹחַ לְהִתְרַקֵּם בָּהּ וַאֲכָלָהּ מַכִּין אוֹתוֹ מַכַּת מַרְדּוּת:
כסף משנה
8.
When one partakes of the egg of a non-kosher fowl inside of which an embryo has begun to take form, he is liable for eating a flying teeming animal.14The embryo is not considered as a non-kosher fowl. Nevertheless, it is already a distinct entity. Hence it is considered as a non-kosher teeming animal. The Maggid Mishneh mentions that there are other Rishonim who do not accept the Rambam's position.
The Siftei Cohen 15:1 explains that while the embryo is within the egg, it has the characteristics of a teeming animal.
If, however, one partakes of the egg of a kosher fowl inside of which an embryo has begun to take form, he is liable for stripes for rebellious conduct.15From Chullin 64a, it appears that there is only a Rabbinic prohibition against partaking of this embryo. Hence, this punishment is given.

הלכה ט
נִמְצָא עָלֶיהָ קֹרֶט דָּם. אִם עַל הַחֶלְבּוֹן זוֹרֵק אֶת הַדָּם וְאוֹכֵל אֶת הַשְּׁאָר. וְאִם עַל הַחֶלְמוֹן אֲסוּרָה כֻּלָּהּ. בֵּיצָה הַמּוּזֶרֶת הַנֶּפֶשׁ הַיָּפָה תֹּאכְלֶנָּה:
כסף משנה
9.
[The following laws apply if] a blood spot is found on an egg.16This refers to an egg that could have been fertilized. If, however, we know that an egg was not fertilized, it is acceptable no matter where the blood spot is found. The blood itself, however, must be discarded [the Shulchan Aruch (Yoreh De'ah 66:7)]. Most of the eggs commercially sold are not fertilized. If it is found on the white, one should discard the blood and eat the remainder of the egg.17For the embryo has not begun to form and has not affected the entire egg. If it is found on the yolk, the entire egg is forbidden.18At this stage of development, the entire egg has been affected. See the Shulchan Aruch and Rama (Yoreh De'ah 66:2-3) which also mention other halachic perspectives with regard to blood found in fertilized eggs. Unfertilized eggs - a refined person partakes of them.19Even though they could be considered spoiled [see Rashi, Chullin 77a; Rama (Yoreh De'ah 66:7)].

הלכה י
אֶפְרוֹחַ שֶׁנּוֹלַד אַף עַל פִּי שֶׁלֹּא נִתְפַּתְּחוּ עֵינָיו מֻתָּר לְאָכְלוֹ. בְּהֵמָה טְהוֹרָה שֶׁנִּטְרְפָה חֲלָבָהּ אָסוּר כַּחֲלֵב בְּהֵמָה טְמֵאָה. וְכֵן בֵּיצַת עוֹף טָהוֹר שֶׁנִּטְרַף כְּבֵיצַת עוֹף טָמֵא וְאָסוּר:
כסף משנה
10.
When a chick is hatched, even if its eyes have not opened, it is permitted [to slaughter it and] eat it.20Until it is hatched, however, it is forbidden as indicated by Halachah 8. See also Siftei Cohen 15:2 who mentions authorities who suggest that one should wait until its wings start to develop before slaughtering it.
When a kosher animal became trefe,21Forbidden because it contracted a wound that will cause it to die within a year. its milk is forbidden like the milk of a non-kosher animal.22Although the milk comes from a kosher species, since the animal itself is unacceptable, its milk is also deemed unacceptable. Similarly, the egg of a kosher fowl that became trefe is comparable to the egg of a non-kosher fowl and is forbidden.23According to Rabbinic decree, this law applies to eggs that are found within a fowl that died without being ritually slaughtered [Shulchan Aruch (Yoreh De'ah 86:3)].

הלכה יא
אֶפְרוֹחַ שֶׁנּוֹלַד מִבֵּיצַת טְרֵפָה מֻתָּר שֶׁאֵין מִינוֹ טָמֵא. הָיָה הָעוֹף סְפֵק טְרֵפָה כָּל הַבֵּיצִים שֶׁתֵּלֵד בַּעֲרֵמָה רִאשׁוֹנָה מַשְׁהִין אוֹתָן. אִם טָעֲנָה עֲרֵמָה שְׁנִיָּה וְהִתְחִילָה לֵילֵד הֻתְּרוּ הָרִאשׁוֹנוֹת שֶׁאִם הָיְתָה טְרֵפָה לֹא הָיְתָה יוֹלֶדֶת עוֹד. וְאִם לֹא יָלְדָה הֲרֵי הֵן אֲסוּרוֹת:
כסף משנה
11.
When a chick is hatched from an egg from a trefe fowl, it is permitted, for it is not from a non-kosher species.24Chulin 31a states that the fact that the egg from which the embryo is formed is trefe does not present a halachic problem. The rationale is that, for the embryo to form, the egg must decompose. Hence its halachic status does not affect that of the embryo. When there is an unresolved question whether a fowl is trefe or not, we retain25For 21 days [Bechorot 8a; the Shulchan Aruch (Yoreh De'ah 86:99]. This is the amount of time our Sages thought necessary for a fowl to begin laying a new batch of eggs. all the eggs it lays in its first batch.26I.e., the eggs it was carrying when it first became trefe. Although Chulin 58a states that a fowl which is trefe will not lay eggs, the intent is that it will not lay a new batch of eggs. It will, however, lay the batch it is presently carrying. If it grows another batch and begins laying them, the first ones are permitted.27There are opinions in the Ashkenazic halachic tradition that forbid such a chick. The Rama (Yoreh De'ah 86:7) states that the initial and preferred option is to respect these views. For if it was trefe, it would no longer lay eggs. If it does not lay eggs, [the first batch] are forbidden.

הלכה יב
חֲלֵב בְּהֵמָה טְמֵאָה אֵינוֹ נִקְפֶּה וְעוֹמֵד כַּחֲלֵב הַטְּהוֹרָה. וְאִם נִתְעָרֵב חֲלֵב טְמֵאָה בַּחֲלֵב בְּהֵמָה טְהוֹרָה כְּשֶׁתַּעֲמִיד אוֹתוֹ יַעֲמוֹד חֲלֵב הַטְּהוֹרָה וְיֵצֵא חֲלֵב הַטֻּמְאָה עִם הַקּוֹם שֶׁל גְּבִינָה:
כסף משנה
12.
The milk of a non-kosher animal will not congeal and solidify as the milk of a kosher animal does. If the milk of a non-kosher animal is mixed together with the milk of a kosher animal, when the mixture is [set aside for cheese to be made], the kosher milk will solidify and the non-kosher milk will be expelled together with the whey of the cheese.

הלכה יג
וּמִפְּנֵי זֶה יִתֵּן הַדִּין שֶׁכָּל חָלָב הַנִּמְצָא בְּיַד עַכּוּ''ם אָסוּר שֶׁמָּא עֵרֵב בּוֹ חֲלֵב בְּהֵמָה טְמֵאָה. וּגְבִינַת הָעַכּוּ''ם מֻתֶּרֶת שֶׁאֵין חֲלֵב בְּהֵמָה טְמֵאָה מִתְגַּבֵּן. אֲבָל בִּימֵי חַכְמֵי מִשְׁנָה גָּזְרוּ עַל גְּבִינַת הָעַכּוּ''ם וַאֲסָרוּם מִפְּנֵי שֶׁמַּעֲמִידִין אוֹתָהּ בְּעוֹר קֵבָה שֶׁל שְׁחִיטָתָן שֶׁהִיא נְבֵלָה. וְאִם תֹּאמַר וַהֲלֹא עוֹר הַקֵּבָה דָּבָר קָטָן הוּא עַד מְאֹד בֶּחָלָב שֶׁעָמַד בּוֹ וְלָמָּה לֹא יִבָּטֵל בְּמִעוּטוֹ. מִפְּנֵי שֶׁהוּא הַמַּעֲמִיד הַגְּבִינָה. וְהוֹאִיל וְדָבָר הָאָסוּר הוּא שֶׁהֶעֱמִיד הֲרֵי הַכּל אָסוּר כְּמוֹ שֶׁיִּתְבָּאֵר:
כסף משנה
13.
Accordingly, logic would dictate that any milk found in the possession of a gentile is forbidden, lest the gentile have mixed the milk of a non-kosher animal with it. And the cheese of the gentiles should be permitted, for the milk of a non-kosher animal will not form cheese. Nevertheless, during the age of the Sages of the Mishnah, they issued a decree against gentile cheese and forbade it, lest they use the skin of the stomach of an animal they slaughtered - which is forbidden as a nevelah28This term refers to an animal from a kosher species which died without being ritually slaughtered. - to cause it to solidify.29For milk to solidify as cheese, it needs a catalyst, rennin, to cause it to curdle. One of the most common sources of rennin was the digestive organs of an animal. For the enzymes that facilitate the digestion of food also produce such an effect. Using the skin of a non-kosher organ causes the cheese to be non-kosher for the reasons the Rambam proceeds to explain. See also Chapter 4, Halachah 19, and Chapter 9, Halachah 15.
As the Ra'avad and Maggid Mishneh mention, Avodah Zarah 35a gives several additional reasons for these prohibitions. The Rambam, however, does not mention them because the factors causing the prohibition could be nullified as explained in the following note. The Maggid Mishneh mentions that there are opinions that maintain that the motivating factor behind the prohibition against non-Jewish cheese is to prevent social interaction between Jews and non-Jews. Hence the prohibitions are never nullified even if there is a substantially larger quantity of the kosher substance.

If one would say: The stomach skin is a very small entity when compared to the milk that it is used to solidify. Why is it not nullified because of its insignificant size?30As will be explained, according to Scriptural Law, when a forbidden substance is mixed together with a kosher substance, it is nullified - i.e, considered as if it has become part of the permitted substance - if the quantity of the permitted substance is greater than it. According to Rabbinic Law, this is true when the quantity of the permitted substance is so great that the taste of the forbidden substance would not be detected. That would certainly be true in the instance at hand. Nevertheless, the forbidden substance is not nullified for the reason explained by the Rambam. Because it is used as the catalyst to cause the cheese to curdle. Since the catalyst which causes it to curdle is forbidden, everything is forbidden, as will be explained.31Chapter 9, Halachah 16; Chapter 16, Halachah 26.

הלכה יד
גְּבִינָה שֶׁמַּעֲמִידִין אוֹתָהּ הָעַכּוּ''ם בַּעֲשָׂבִים אוֹ בְּמֵי פֵּרוֹת כְּגוֹן שְׂרַף הַתְּאֵנִים וַהֲרֵי הֵן נִכָּרִין בַּגְּבִינָה הוֹרוּ מִקְצָת הַגְּאוֹנִים שֶׁהִיא אֲסוּרָה. שֶׁכְּבָר גָּזְרוּ עַל כָּל גְּבִינַת הָעַכּוּ''ם בֵּין שֶׁהֶעֱמִידוּהָ בְּדָבָר אָסוּר בֵּין שֶׁהֶעֱמִידוּהָ בְּדָבָר הַמֻּתָּר גְּזֵרָה מִשּׁוּם שֶׁמַּעֲמִידִין אוֹתָהּ בְּדָבָר הָאָסוּר:
כסף משנה
14.
[The following laws apply when] cheese is left to solidify with herbs or fruit juice, e.g., fig syrup, and it is apparent [that these substances were used for] the cheese. There are some of the Geonim who have ruled that it is forbidden, for [our Sages] already decreed that all the cheeses of gentiles are forbidden, whether they caused them to solidify with a forbidden entity or with a permitted entity.32This is also the Rambam's view. It is quoted by the the Shulchan Aruch (Yoreh De'ah 115:2. The Rama states that it is customary to follow this view. The Rama continues, stating that when a Jew observes a gentile milking the cows and making the cheese, it is permitted to partake of it even though the cheese belongs to the gentiles. He continues, stating that even if the Jew does not observe the gentile milking the cow, as long as he observes him making the cheese, the cheese is acceptable after the fact. The Turei Zahav 115:11 and the Siftei Cohen 115:22 quote opinions that differ and maintain that the prohibition should be observed even if a Jew did not observe the milking.
This difference of opinion is relevant today, reflecting the difference between chalav Yisrael cheese and ordinary kosher cheese. In both instances, the cheesemaking process is supervised. Chalav Yisrael cheese uses milk that was supervised when milked, while ordinary kosher cheese does not.
This is a decree, [instituted] because they cause them to solidify using forbidden entities.

הלכה טו
הָאוֹכֵל גְּבִינַת הָעַכּוּ''ם אוֹ חָלָב שֶׁחֲלָבוֹ עַכּוּ''ם וְאֵין יִשְׂרָאֵל רוֹאֵהוּ מַכִּין אוֹתוֹ מַכַּת מַרְדּוּת. הַחֶמְאָה שֶׁל עַכּוּ''ם מִקְצָת הַגְּאוֹנִים הִתִּירוּהָ שֶׁהֲרֵי לֹא גָּזְרוּ עַל הַחֶמְאָה וַחֲלֵב הַטְּמֵאָה אֵינוֹ עוֹמֵד. וּמִקְצָת הַגְּאוֹנִים אֲסָרוּהָ מִפְּנֵי צִחְצוּחֵי חָלָב שֶׁיִּשָּׁאֵר בָּהּ. שֶׁהֲרֵי הַקּוֹם שֶׁבַּחֶמְאָה אֵינוֹ מְעֹרָב עִם הַחֶמְאָה כְּדֵי שֶׁיִּבָּטֵל בְּמִעוּטוֹ. וְכָל חָלָב שֶׁלָּהֶן חוֹשְׁשִׁין לוֹ שֶׁמָּא עֵרְבוּ בּוֹ חֲלֵב בְּהֵמָה טְמֵאָה:
כסף משנה
15.
When a person partakes of cheese from gentiles or milk that was milked by a gentile without a Jew observing him, he is given stripes for rebellious conduct.33For his behavior is in violation of an explicit Rabbinic prohibition. Even though the rationale for the original decree is no longer applicable, the prohibition established by our Rabbis is still in force. (See Hilchot Mamrim 2:2.)
In the present era, there are certain Rabbis (see Rav Moshe Feinstein, Igros Moshe) who give a rationale for leniency with regard to this prohibition, stating that government supervision makes it impossible for gentiles to mix non-kosher milk together with cow's milk and thus there is no necessity to heed that prohibition. It must be emphasized, however, that this responsum was authored before the time when it became relative easy to procure chalav Yisrael and that many other Rabbinical authorities never accepted this decision. On the contrary, basing themselves on the ruling of Hilchot Mamrim 2:2, they explain that the original decree must still be observed. As a result of their forceful stance, at present, it is possible to obtain chalav Yisrael products in almost every major Jewish community.
With regard to butter produced by gentiles, some of the Geonim permit it, for [our Sages] did not decree against butter and some of the Geonim forbid it,34The Shulchan Aruch (Yoreh De'ah 115:3) states that one should not rebuke those who permit the use of such butter, but if the local custom is to forbid it, that custom should be respected. At present, since it is possible to obtain chalav Yisrael butter in almost every major Jewish community, many Rabbis urge that this prohibition be observed. because of the drops of milk that remain in it. For the whey in the butter is not mixed with the butter35We are speaking about homemade butter which always has some small drops of whey within it. These drops, however, are not mixed with the butter itself, but instead remain as a separate entity. Hence, they cannot be nullified. See Kessef Mishneh. so that it will be nullified because of its minimal quantity. And we suspect that any milk [from gentiles] is mixed with the milk of a non-kosher animal.

הלכה טז
יֵרָאֶה לִי שֶׁאִם לָקַח חֶמְאָה מִן הָעַכּוּ''ם וּבִשְּׁלָהּ עַד שֶׁהָלְכוּ לָהֶן צִחְצוּחֵי חָלָב הֲרֵי זוֹ מֻתֶּרֶת. שֶׁאִם תֹּאמַר נִתְעָרְבוּ עִמָּן וְנִתְבַּשְּׁלוּ כֻּלָּן בָּטְלוּ בְּמִעוּטָם. אֲבָל הַחֶמְאָה שֶׁבִּשְּׁלוּ אוֹתָהּ עַכּוּ''ם אֲסוּרָה מִשּׁוּם גִּעוּלֵי עַכּוּ''ם כְּמוֹ שֶׁיִּתְבָּאֵר:
כסף משנה
16.
It appears to me36This expression connotes a law derived by the Rambam through his deductive reasoning without an existing prior Rabbinic source. that if one purchased butter from gentiles and cooked it until the drops of milk in it disappeared, it is permitted.37The Kessef Mishneh explains that not only is this permitted after the fact, one may do so at the outset (lechatchilah). For it is possible that there is no forbidden substance present at all.
The Rama (Yoreh De'ah 115:3) quotes this ruling. Nevertheless, most of the authorities who forbid using non-Jewish butter maintain that, in practice, one should refrain from cooking it as well.
For if one will say that [drops of non-kosher milk] were mixed with the butter and it was all cooked together, they became insignificant because of the small quantity [involved].38I.e., the amount of non-kosher milk is surely insignificant in relation to the quantity of the mixture as a whole. Hence it is nullified. When, however, the butter is cooked by gentiles themselves,39I.e., in their own utensils. it is forbidden because of the effusion of gentile [foods], as will be explained.40As explained in Chapter 17, Halachah 2, it is forbidden to cook food in utensils belonging to gentiles, for the utensil will have absorbed some of the non-kosher food cooked in it previously and will discharge it into the kosher food during the cooking process.
The Kessef Mishneh and the Rama (loc. cit.) differ with the Rambam regarding this issue. See the notes to Chapter 17 Halachah 18, for a discussion of this matter.

הלכה יז
יִשְׂרָאֵל שֶׁיָּשַׁב בְּצַד הָעֵדֶר שֶׁל נָכְרִי וּבָא הַנָּכְרִי וְהֵבִיא לוֹ חָלָב מִן הָעֵדֶר אַף עַל פִּי שֶׁיֵּשׁ בָּעֵדֶר בְּהֵמָה טְמֵאָה הֲרֵי זוֹ מֻתָּר. וְאַף עַל פִּי שֶׁלֹּא רָאָה אוֹתוֹ חוֹלֵב. וְהוּא שֶׁיָּכוֹל לִרְאוֹתוֹ כְּשֶׁהוּא חוֹלֵב כְּשֶׁיַּעֲמֹד. שֶׁהַנָּכְרִי מִתְיָרֵא לַחֲלֹב מִן הַטְּמֵאָה שֶׁמָּא יַעֲמֹד וְיִרְאֶה אוֹתוֹ:
כסף משנה
17.
When a Jew sits near a herd belonging to a gentile and the gentile brings him milk from the herd, it is permitted [for him to partake of it] even though there are non-kosher animals in the herd. [This applies] even though he did not see him milk the animal, provided he could have seen him were he to stand.41Similarly, if the Jew walks in and out of the place where the milking is taking place, it is acceptable. For the gentile will fear that any moment, the Jew will return (Turei Zahav 115:3). [The rationale is that] the gentile is afraid to milk the non-kosher animal lest [the Jew] stand and see him.42The Rambam is explaining that although our Sages require that a Jew observe the milking of an animal, it is not necessary that he watch the actual milking. As long as he is present and could see what the gentile is doing, the gentile will refrain from mixing in a non-kosher substance.
The Rama (Yoreh De'ah 115:1) states that this ruling applies only after the fact. At the outset, the Jew must observe the milking and also check the container into which the gentile is milking.
The Maggid Mishneh clarifies that this ruling applies only when the gentile is milking the animal for the Jew and knows that the Jew will not drink the milk of the non-kosher animal. If he is not aware of the prohibition, we suspect that he will give the Jew milk from any animal in his herd.

הלכה יח
בֵּיצָה שֶׁשְּׁנֵי רָאשֶׁיהָ כַּדִּין אוֹ שֶׁשְּׁנֵי רָאשֶׁיהָ חַדִּין. אוֹ שֶׁהָיָה חֶלְמוֹן מִבַּחוּץ וְחֶלְבּוֹן מִבִּפְנִים בְּיָדוּעַ שֶׁהוּא בֵּיצַת עוֹף טָמֵא. רֹאשָׁהּ אֶחָד כַּד וְרֹאשָׁהּ אֶחָד חַד וְחֶלְבּוֹן מִבַּחוּץ וְחֶלְמוֹן מִבִּפְנִים. אֶפְשָׁר שֶׁהִיא בֵּיצַת עוֹף טָמֵא וְאֶפְשָׁר שֶׁהִיא בֵּיצַת עוֹף טָהוֹר. לְפִיכָךְ שׁוֹאֵל לַצַּיָּד יִשְׂרָאֵל שֶׁמּוֹכְרָהּ. אִם אָמַר לוֹ שֶׁל עוֹף פְּלוֹנִי הוּא וְעוֹף טָהוֹר הוּא סוֹמֵךְ עָלָיו. וְאִם אָמַר שֶׁל עוֹף טָהוֹר וְלֹא אָמַר לוֹ שְׁמוֹ אֵינוֹ סוֹמֵךְ עָלָיו:
כסף משנה
18.
When both of the ends of an egg are rounded, both are pointed, or the yolk is on the outside and the white is on the inside, it is certainly from a non-kosher species. If one end is pointed, the other rounded, and the white is on the outside and the yolk is on the inside, it is possible that it is the egg of a non-kosher species and it is possible that it is the egg of a kosher species.43I.e., all kosher eggs have these characteristics, but not all eggs with these characteristics are kosher. Accordingly, the Jew should inquire of the Jewish44But not a non-Jewish hunter, as evident from the following halachah. hunter who sells them. If he tells him that they are from such-and-such a fowl and that this fowl is kosher, he may rely on him.45We are certain that he will not lie, because it is possible to bring other eggs from that species and see that they are not alike (Turei Zahav 86:1; Siftei Cohen 86:3). If, however, he tells him that they are from a kosher fowl, but does not mention its name, he may not rely on him.46For the method of verification mentioned in the previous note does not apply.
The Ra'avad rules that if the hunter has an established reputation for observance, we may rely on his word, even though he does not name the species of the fowl. The Maggid Mishneh states that, as indicated by the conclusion of Halachah 20, the Rambam would also accept that ruling. According to this understanding, the hunter we are speaking about is not known for his observance. Nevertheless, we rely on his statements.
In his notes to Halachah 20, the Rashba emphasizes that we are not speaking about a person who is known to sell non-kosher food as kosher. As evident from Hilchot Maaserot 12:16, such a person is considered as a gentile and his word is not accepted at all. Instead, the intent is someone whose reputation for observance has not been established, but is also not suspect to cause others to transgress.

הלכה יט
לְפִיכָךְ אֵין לוֹקְחִים בֵּיצִים מִן הָעַכּוּ''ם אֶלָּא אִם הָיָה מַכִּיר אוֹתָן וְיֵשׁ לוֹ בָּהֶן טְבִיעוּת עַיִן שֶׁהֵן בֵּיצֵי עוֹף פְּלוֹנִי הַטָּהוֹר. וְאֵין חוֹשְׁשִׁין לָהֶן שֶׁמָּא הֵן בֵּיצֵי טְרֵפָה אוֹ בֵּיצֵי נְבֵלָה. וְאֵין לוֹקְחִין מִן הָעַכּוּ''ם בֵּיצָה טְרוּפָה כְּלָל:
כסף משנה
19.
For this reason, we do not purchase eggs from gentiles unless one recognizes the eggs and can identify them as being from a particular kosher species of fowl.47The Maggid Mishneh quotes the Ramban who differs with the Rambam and maintains that there is no difference between a Jew whose reputation for observance is not established and a gentile. Just like we accept the Jew's word, we accept that of the gentile. For we assume that he will not risk his reputation by making false statements. The Shulchan Aruch (Yoreh De'ah 86:1) quotes the Rambam's ruling, while the Tur and the Rama cite that of the Ramban.
The Maggid Mishneh also quotes Rashba who states that in the present age, we purchase eggs from gentiles without compunction, because non-kosher species are uncommon and the overwhelming proportion of eggs sold are from chickens or geese. This ruling is quoted by the Shulchan Aruch (Yoreh De'ah 86:2).
We do not suspect that they came from a fowl that was trefe or nevelah.48I.e., that died without being ritually slaughtered; see Chapter 4, Halachah 1. We rule leniently, because it is very uncommon to have eggs from fowl in such a condition (Maggid Mishneh). And we do not purchase an [unshelled and] stirred egg from a gentile at all.49For we fear that it came from an egg that was trefe (Maggid Mishneh).

הלכה כ
בֵּיצֵי דָּגִים סִימָנֵיהֶם כְּסִימָנֵי בֵּיצֵי הָעוֹף. אִם הָיוּ שְׁנֵי רָאשֶׁיהָ כַּדִּין אוֹ חַדִּין טְמֵאָה. אֶחָד כַּד וְאֶחָד חַד שׁוֹאֵל לְיִשְׂרְאֵלִי הַמּוֹכֵר. אִם אָמַר לוֹ אֲנִי מְלַחְתִּים וְהוֹצֵאתִים מִדָּג טָהוֹר אוֹכֵל עַל פִּיו. וְאִם אָמַר לוֹ טְהוֹרִין הֵם אֵינוֹ נֶאֱמָן אֶלָּא אִם כֵּן הָיָה אָדָם שֶׁהֻחְזַק בְּכַשְׁרוּת:
כסף משנה
20.
The distinguishing signs of fish eggs are the same as those for fowl. When both of the ends of an egg are rounded or both are pointed, it is non-kosher. If one end is pointed and the other rounded, he should inquire of the Jew who sells them.50For the distinguishing signs themselves are not sufficient for the eggs to be considered kosher. The Maggid Mishneh explains that although Avodah Zarah 40a would appear to indicate that the distinguishing signs are sufficient, since Chullin 64a compares fish eggs to fowl eggs, we assume that all the laws that apply to one apply to the other.
In his Shulchan Aruch (Yoreh De'ah 83:8), Rav Yosef Caro quotes the Rambam's ruling, but states that at present, it has become customary to buy any red fish eggs, even from gentiles. Black fish eggs, however, may not be purchased. In his Beit Yosef 81:12, he explains that the Rabbinic authorities of the earlier ages researched the matter and discovered that there are no common non-kosher fish that lay red eggs. See Siftei Cohen 83:27 who quotes other sources from which it is not clear whether or not this ruling was accepted in all communities.
If he tells him that he salted them51I.e., to preserve them, for it is common to bring fish eggs from distant places. and removed them from a kosher species,52Naming the species as in Halachah 18. he may partake of them on the basis of his statements. If he tells him that they are kosher, he may not rely on him unless he is a person who has an established reputation for observance.

הלכה כא
וְכֵן אֵין לוֹקְחִין גְּבִינָה וַחֲתִיכַת דָּג שֶׁאֵין בָּהּ סִימָן אֶלָּא מִיִּשְׂרְאֵלִי שֶׁהֻחְזַק בְּכַשְׁרוּת. אֲבָל בְּאֶרֶץ יִשְׂרָאֵל כְּשֶׁהָיְתָה רֻבָּהּ יִשְׂרָאֵל לוֹקְחִין מִכָּל יִשְׂרְאֵלִי שֶׁבָּהּ. וְהֶחָלָב לוֹקְחִין אוֹתוֹ מִכָּל יִשְׂרָאֵל מִכָּל מָקוֹם:
כסף משנה
21.
Similarly, we may not purchase cheese and pieces of fish that do not have distinguishing signs except from a Jew who has an established reputation for observance. In Eretz Yisrael, at the time it was populated primarily by [observant] Jews,53As indicated by Chapter 11, Halachah 25, today, the same principles that apply in the Diaspora apply in Eretz Yisrael. one could purchase these items from any Jew located there. And it is permitted to purchase milk from any Jew, anywhere.

הלכה כב
הַכּוֹבֵשׁ דָּגִים טְמֵאִים צִירָן אָסוּר. אֲבָל צִיר חֲגָבִים טְמֵאִים מֻתָּר מִפְּנֵי שֶׁאֵין בָּהֶם לַחְלוּחִית. לְפִיכָךְ אֵין לוֹקְחִין צִיר מִן הָעַכּוּ''ם אֶלָּא אִם כֵּן הָיָה בּוֹ דָּג טָהוֹר מְשׁוֹטֵט בּוֹ אֲפִלּוּ דָּג אֶחָד:
כסף משנה
22.
When a person pickles non-kosher fish, the brine produced is forbidden. The brine produced by non-kosher locusts, by contrast, is permitted, because they do not possess any moisture.54In the Rambam's Commentary to the Mishnah (Terumot 10:9), he states that they possess very little moisture. The Ra'avad differs with the Rambam's ruling and forbids brine from non-kosher locusts. Accordingly, we do not purchase brine from gentiles unless there is a kosher fish floating in it.55For then we assume that the brine came from this species of fish. Even one fish is sufficient.

הלכה כג
עַכּוּ''ם שֶׁהֵבִיא עֲרֵבָה מְלֵאָה חָבִיּוֹת פְּתוּחוֹת שֶׁל צִיר וְדָג אֶחָד טָהוֹר בְּאַחַת מֵהֶם כֻּלָּן מֻתָּרוֹת. הָיוּ סְתוּמוֹת פָּתַח אַחַת וְנִמְצָא בָּהּ דָּג טָהוֹר שְׁנִיָּה וְנִמְצָא בָּהּ טָהוֹר כֻּלָּן מֻתָּרוֹת. וְהוּא שֶׁיִּהְיֶה רֹאשׁוֹ שֶׁל דָּג וּשְׁדֵרוֹ קַיָּם כְּדֵי שֶׁיְּהֵא נִכָּר שֶׁהוּא דָּג טָהוֹר. לְפִיכָךְ אֵין לוֹקְחִין דָּגִים מְרוֹצָצִין מְלוּחִין מִן הָעַכּוּ''ם וְהֵם הַנִּקְרָאִים טָרִית טְרוּפָה. וְאִם הָיָה רֹאשׁ הַדָּג וּשְׁדֵרוֹ נִכָּר אַף עַל פִּי שֶׁהוּא מְרוֹצָץ מֻתָּר לִקַּח אוֹתוֹ מִן הָעַכּוּ''ם:
כסף משנה
23.
When a gentile brings a trough filled with open barrels of brine and there is a kosher fish in one of them, they are all permitted.56For we consider all the open barrels as a single entity and the one fish indicates that the entire quantity is acceptable. See Kessef Mishneh. This represents the Rambam's understanding of Avodah Zarah 39b-40a. The rulings of the Shulchan Aruch (Yoreh De'ah 83:6) quotes the Rambam's ruling, but also those of others who interpret that passage differently. If they are closed, one opens one and finds a kosher fish and one opens a second and finds a kosher fish, they are all permitted.57The intent is not that all the barrels are considered as a single entity, but that since two barrels are discovered to be kosher, we assume that the others are also kosher (Kessef Mishneh). [This applies] provided the head of the fish and its backbone are present so that it is recognizable that they are from a kosher species of fish.58I.e., by looking at the head and the backbone, the person is able to recognize that the fish comes from a kosher species. One alone, i.e., either the head or the backbone, is not sufficient (Avodah Zarah 40a).
For this reason, we do not purchased crushed, salted fish from gentiles which are called terit terufah.59In his Commentary to the Mishnah (Avodah Zarah 2:6), the Rambam explains that it was customary to crush and stir the fish until it produces a mixture like dough that was used as a dip. If, however, the head and the backbone of a fish is recognizable, even though it is crushed, it is permitted to purchase it from a gentile.60I.e., if we discover the head and the backbone of one fish, we may purchase a larger quantity, because we do not expect that kosher fish and non-kosher fish were salted together (Maggid Mishneh).

הלכה כד
עַכּוּ''ם שֶׁהֵבִיא גָּרָב שֶׁל חֲתִיכוֹת דָּג שֶׁחִתּוּכָן שָׁוֶה וְהֵן נִכָּרִין שֶׁכֻּלָּן מִדָּג אֶחָד וּמָצָא בַּחֲתִיכָה אַחַת מֵהֶן קַשְׂקַשִּׂין הֲרֵי כֻּלָּן מֻתָּרוֹת:
כסף משנה
24.
When a gentile brings a keg of pieces of evenly cut up fish and it is obvious that they are from one fish,61The Siftei Cohen 83:4 notes that the Shulchan Aruch (Yoreh De'ah 83:4) does not quote the Rambam's wording and explains that according to that source, it is not necessary for it to be obvious that they all come from one fish.
If it is not obvious that they come from one fish, the Shulchan Aruch (loc. cit.) rules that only the piece with scales is permitted.
they are all permitted if he finds scales on one of the pieces.62For every fish that has scales will also have fins.

קדושה הלכות מאכלות אסורות פרק ג
Kedushah Ma`akhalos Assuros Chapter 3