The taste of a non-Jew (טעימת קפילא), annulment by sixty (ביטול בס׳), stirring and covering (ניער / כיסה), חתיכה נעשית נבילה, the drop on the wall of the pot, תתאה גבר, vapor (זיעה) and the tallow candle (Shulchan Aruch, Yoreh De'ah 92 — 9 se'ifim)
כְּזַיִת בָּשָׂר שֶׁנָּפַל לְתוֹךְ יוֹרָה שֶׁל חָלָב רוֹתֵחַ, טוֹעֵם הָעוֹבֵד כּוֹכָבִים הַקְּדֵרָה; אִם אָמַר שֶׁיֵּשׁ בָּהּ טַעַם בָּשָׂר אֲסוּרָה, וְאִם לָאו מֻתֶּרֶת — אֲפִלּוּ בְּפָחוֹת מִשִּׁשִּׁים; וְאוֹתָהּ חֲתִיכָה אֲסוּרָה.
A kazayit of meat that fell into a pot of boiling milk: a non-Jew tastes the pot; if he says there is a taste of meat, it is forbidden; if not, it is permitted — even with less than sixty; but that piece is forbidden.
Shulchan Aruch, Yoreh De'ah 92:1LEVEL 01
Hebrew text of the 9 se'ifim with a fluent English translation. The taste of the non-Jew (קפילא), annulment by sixty, stirring and covering (ניער / כיסה), the drop on the wall of the pot, the vapor and the tallow candle explained with practical cases.
📖 StudyLEVEL 02
In-depth pilpul: the sugya of Chullin, the two prohibitions of se'if 1 according to the Taz, the yesod of חתיכה נעשית נבילה, the מחלוקת Rashi / R"I on the צירוף, the Ran's debate (Shach sk3) on the piece outside the liquid, חקירות and נפקא מינות.
📖 StudyLEVEL 03
Comparative tables (before / after removal, stirred-covered or not, כנגד הרוטב / כנגד הריקן), golden rules, classic pitfalls (חנ״נ, מפעפע, תתאה גבר, זיעה) and memorization of the 9 se'ifim.
📖 StudyLEVEL 04
The practical halacha according to the Shach, Taz, Pri Megadim and Pitchei Teshuva, then the Sephardic poskim (Yabia Omer, Yalkut Yosef, Or LeTzion) and Ashkenazi poskim. Note: the Shulchan Aruch HaRav does not deal with this siman — this is a level of psak, not "Daat HaRav".
📖 StudyAccording to the Shulchan Aruch (YD 92:1), when a kazayit of meat falls into a pot of boiling milk, a non-Jew (קפילא) tastes it: if he senses no taste of meat, the milk is permitted even with less than sixty. But the Rama (הגה) rules that we do not have the custom to rely on the taste of a non-Jew (אין אנו נוהגין לסמוך אטעימת עובד כוכבים) and that we require 60 in every case (בעינן ס׳ בכל ענין). For practical halacha, consult your Rav.
This is the principle of se'ifim 3-4: when a piece of heter absorbs a prohibition without there being 60 to nullify it, the entire piece itself becomes forbidden (נעשית כל החתיכה נבילה). Cooked afterwards with others, one then needs 60 against the whole piece, not only against the absorbed prohibition. The Shulchan Aruch states this principle only for basar be-halav; the Rama rules, following the widespread custom, that one applies it to all prohibitions, and one does not deviate from this. For practical halacha, consult your Rav.
It depends on the place (se'ifim 5-6). If the drop falls opposite the liquid (כנגד הרוטב), it diffuses inward (מפעפעת לפנים) and 60 against it within the dish is enough. If it falls on the empty part (כנגד הריקן), above the level, the custom is to forbid that spot on the wall — except on the side of the fire, where the fire burns and dries up the drop (האש שורפו ומייבשו). The remedy, in doubt, is not to touch that spot until it cools. For practical halacha, consult your Rav.