A sharp food (radish, beet, garlic, onion, horseradish…) cut with a meat knife: its sharpness "extracts" and diffuses the absorbed taste; נטילת מקום, קליפה, גרידה or הדחה according to intensity, and the מחלוקת on the "whole is forbidden" (כולו אסור) (Shulchan Aruch, Yoreh De'ah 96 — 5 se'ifim)
צְנוֹן אוֹ סִילְקָא שֶׁחֲתָכָם בְּסַכִּין שֶׁל בָּשָׂר בֶּן יוֹמוֹ, אוֹ שֶׁאֵינוֹ מְקֻנָּח — אָסוּר לְאָכְלָם בְּחָלָב, עַד שֶׁיִּטֹּל מִמְּקוֹם הַחֲתָךְ כְּדֵי נְטִילַת מָקוֹם שֶׁהוּא כְּעֹבִי אֶצְבַּע, אוֹ שֶׁיִּטְעֲמֶנּוּ וְלֹא יְהֵא בּוֹ טַעַם בָּשָׂר, שֶׁאָז מֻתָּר בַּהֲדָחָה.
A radish or a beet cut with a meat knife that is ben yomo or unwiped are forbidden to eat with milk, until one removes at the cut the measure of a netilat makom — the thickness of a finger — or tastes it and detects no taste of meat, in which case a simple rinsing (הדחה) suffices.
Shulchan Aruch, Yoreh De'ah 96:1LEVEL 01
Hebrew text of the 5 se'ifim with a fluent English translation. The radish and beet (צנון / סילקא), other דברים חריפים (garlic, onion, horseradish), spices pounded in a mortar, imported lemon juice and salted fish, the squash and the turnip — explained with practical cases (נטילת מקום, גרידה, הדחה).
📖 StudyLEVEL 02
In-depth pilpul: the yesod of the דבר חריף (חורפיה + דוחקא דסכינא), the מחלוקת Mahara"m / Sefer ha-Teroumot on whether only the חלתית or every חריף (Taz sk1 and sk3), נ"ט בר נ"ט מן הממש, דק דק → כולו אסור, 60 against the whole blade (Rash"al), חקירות and נפקא מינות.
📖 StudyLEVEL 03
Comparative tables (the scale נטילת מקום / קליפה / גרידה / הדחה, ben yomo or not, דק דק or not), golden rules, classic pitfalls (חורפיה, דוחקא דסכינא, כולו אסור, מבטל טעם) and memorization of the 5 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 96:1), a radish (צנון) or beet (סילקא) cut with a meat knife that is ben yomo or unwiped is forbidden with milk, until one removes at the cut a נטילת מקום (the thickness of a finger, כעובי אצבע), or tastes them and detects no taste of meat — in which case a simple rinsing (הדחה) suffices. The Rama adds: if it was cut very fine (דק דק), one needs 60 against the whole radish; and the custom lechatchila, per the Rashba / Ran, is to forbid the whole radish. For practical halacha, consult your Rav.
A דבר חריף is a sharp / pungent food — radish (צנון), beet (סילקא), garlic (שומין), onions (בצלים), leeks (כרישין), horseradish (תמכא / קריי"ן), acidic fruits and salted fish. Through its sharpness (חורפיה) together with the pressure of the knife (אגב דוחקא דסכינא), it extracts the taste absorbed in the blade and diffuses it as substance (ממש); it even "awakens" a taste that would otherwise be weakened (פגום, non-ben-yomo). The talmudic paradigm is the קורט של חלתית (asafetida). For practical halacha, consult your Rav.
It is a graduated scale according to the intensity of the expelled taste (Taz sk14). For the radish, very חריף: נטילת מקום — one removes at the cut the thickness of a finger (כעובי אצבע); below that, קליפה (peeling a thin layer). For squash (קישואים), moist and less pungent: גרידה alone (scraping, less than a קליפה). For the turnip (לפת), whose taste is different: even גרידה is not required, a simple הדחה (rinsing) suffices — and the different taste of the turnip even nullifies that of a radish cut after it. For practical halacha, consult your Rav.