The field mouse (עכברא דדברא) is a royal dish → it improves the taste (נ"ט לשבח) and forbids; the city mouse (עכברא דמתא) is a doubt (improves or spoils?): fallen in the cold and removed whole before 24 h, it is permitted; otherwise 60 is needed; but if it broke into fine particles impossible to filter (wine/vinegar in a thick food), everything is forbidden for one might swallow the substance without noticing; in wine, oil (and honey) it certainly spoils (no 60 needed); and the repulsive creatures (ants, flies, gnats) — Shulchan Aruch, Yoreh De'ah 104 — 3 se'ifim
עַכְבָּרָא דְּדַבְרָא נוֹתֵן טַעַם לְשֶׁבַח הוּא, שֶׁהֲרֵי עוֹלֶה עַל שֻׁלְחַן מְלָכִים. אֲבָל עַכְבָּרָא דְּמָתָא מְסֻפָּק לָנוּ אִם מַשְׁבִּיחַ בְּשֵׁכָר וְחֹמֶץ אוֹ אִם הוּא פּוֹגֵם. וּלְפִיכָךְ אִם נָפַל לְשֵׁכָר אוֹ לְחֹמֶץ בְּצוֹנֵן וְהֱסִירוֹ שָׁלֵם, אִם לֹא שָׁהָה בְּתוֹכוֹ מֵעֵת לְעֵת — מֻתָּר.
The field mouse communicates a good taste (נותן טעם לשבח), for it rises onto the table of kings. But for the city mouse, we have a doubt: does it improve the beer and vinegar, or spoil them? Therefore, if it fell into the beer or vinegar in the cold and was removed whole, if it did not remain inside 24 hours (מעת לעת) — it is permitted.
Shulchan Aruch, Yoreh De'ah 104:1LEVEL 01
Hebrew text of the 3 se'ifim with a fluent English translation. The field and city mouse, cold pickling and the 24 hours, the unfilterable prohibition, wine and oil that spoil, and the repulsive creatures explained with practical cases.
📖 StudyLEVEL 02
In-depth pilpul: נ"ט לשבח / לפגם applied to the mouse, the great מחלוקת Taz / Shach-Rama on the דבר הניכר שאי אפשר לבררו (a חומרא of שרץ or the din of every prohibition?), חצי שיעור אסור מן התורה, כבוש כמבושל, the ספק ספיקא of fat, חקירות and נפקא מינות.
📖 StudyLEVEL 03
Comparative tables (field / city, cold / hot, before / after 24 h, filterable / impossible to filter, wine-oil / fat), golden rules, classic pitfalls (נ"ט לפגם, כבוש, דבר הניכר, דברים המאוסים) and memorization of the 3 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".
📖 StudyThe field mouse (עכברא דדברא) "rises onto the table of kings": it is a choice food, so it improves the taste (נותן טעם לשבח) and therefore forbids the liquid into which it falls. For the city mouse (עכברא דמתא), the Shulchan Aruch (YD 104:1) says we have a doubt: does it improve the beer and vinegar, or spoil them? We therefore act stringently: fallen in the cold (בצונן) and removed whole, if it did not remain 24 hours (מעת לעת) it is permitted; otherwise 60 is needed. For practical halacha, consult your Rav.
If the mouse broke into fine particles that can be filtered through a strainer (מסננת), or it fully dissolved (נימוח), it is nullified by 60. But if it broke into particles impossible to filter — for example the wine or vinegar mixed into a thick food (מאכל עב) — everything is forbidden, without nullification, for we fear encountering the very substance of the prohibition (the ממש) without noticing. The Rama sees this as a stringency specific to a שרץ (creeping creature); the Taz extends it to any recognizable, inseparable prohibition. For practical halacha, consult your Rav.
In wine and oil (and honey), the mouse certainly spoils (פוגם בודאי) — which "must be fragrant" — and no 60 is needed (se'if 2). For fat (שומן), the Rama is lenient (נטילת מקום and ספק ספיקא, since כבוש = cooked), but some are stringent as with beer. As for the repulsive things (דברים המאוסים) — ants, flies, gnats — from which a person turns away on his own, they are nullified in the majority of permitted matter even when dissolved, but one filters whatever can be filtered, and in vinegar and beer one remains vigilant as with the mouse (se'if 3). For practical halacha, consult your Rav.