Meat and cheese that touch, salting together, covering, kavush and the principle תתאה גבר (Shulchan Aruch, Yoreh De'ah 91 — 8 se'ifim)
בָּשָׂר וּגְבִינָה שֶׁנָּגְעוּ זֶה בָּזֶה — מֻתָּרִים, אֶלָּא שֶׁצָּרִיךְ לְהָדִיחַ מְקוֹם נְגִיעָתָן; וּמֻתָּר לָצוּר אוֹתָם בְּמִטְפַּחַת אַחַת, וְלֹא חָיְישִׁינַן שֶׁמָּא יִגְּעוּ זֶה בָּזֶה.
Meat and cheese that have touched (while cold) are permitted; one need only rinse the point of contact (להדיח מקום נגיעתן). And it is permitted to wrap them in a single cloth — we are not concerned that they may come to touch each other.
Shulchan Aruch, Yoreh De'ah 91:1LEVEL 01
Hebrew text of the 8 se'ifim with a fluent English translation. Cold contact, rinsing (הדחה), תתאה גבר, the קליפה, salting treated like something boiling, and the key concepts explained with practical cases.
📖 StudyLEVEL 02
In-depth pilpul: the sugya of Chullin and Pesachim, the yesod of תתאה גבר, the מחלוקת Shach/Taz on salting and ציר, the ריב״א debate on ס׳ versus the קליפה, חקירות and נפקא מינות.
📖 StudyLEVEL 03
Comparative tables (hot/cold, salted/unsalted, צלי), golden rules, classic pitfalls (תתאה גבר, ציר, בקעים) and memorization of the 8 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".
📖 StudyNo, not if they were cold. The Shulchan Aruch (YD 91:1) teaches that meat and cheese that touch while cold remain permitted; it is enough to rinse the point of contact (להדיח מקום נגיעתן). The Shach (s.k. 1, in the name of the Bayit Chadash) adds that if both are completely dry, even rinsing is not necessary. Everything changes if there is heat or salting. For practical halacha, consult your Rav.
This is the central principle of se'if 4. When a hot food and a cold one meet, the lower one prevails (תתאה גבר). If the lower one is hot, it heats the upper one and everything is forbidden. If the lower one is cold, it cools the upper one, which absorbed only at the surface: it is then enough to peel (קליפה). The Shulchan Aruch applies this to boiling meat and milk that fell one upon the other.
Salting (מליחה) that makes a food « not edible because of its salt » (אינו נאכל מחמת מלחו) is treated like something boiling and forbids כדי קליפה (the thickness of a peel). Likewise the salty brine (ציר) is considered as boiling. The principle of the salted item (se'if 5): the salted one makes flavor enter the unsalted one and does not absorb from it (המליח מבליע בתפל ואינו בולע ממנו). But note: melicha and kavush forbid only for eating, never for benefit (se'if 8). For practical halacha, consult your Rav.