Taste (Ta'am) Transfer: Spicy/Charif: Pressure: Food Absorbing Taste of Utensils

When a spicy/charif food takes on the gender of the cutting/squeezing utensil:
  • You may not cook or eat that food with food of the opposite gender.
  • However, you MAY eat the opposite-gender food immediately after eating the gendered spicy food without waiting.
Situation An onion is cut with a meat knife, on a meat cutting board:
  • The onion acquires meat status.
  • You MAY NOT later cut this onion with a dairy knife or on a dairy cutting board. (If you do, the onion, the dairy knife, and the dairy cutting board will all become non-kosher.) 
Exception If the knife and cutting board had not been used (even for cold items) for at least 24 hours, consult a rabbi.
Exception If you can sand off the surface to below the level of any knife cuts, the board might be kosher. Consult a rabbi. 
  • You MAY NOT cook this onion in a dairy utensil.
  • You MAY NOT eat this onion with dairy food.
  • You MAY eat dairy immediately after eating this onion (as long as there is no actual meat mixed into the onion).
  • You MAY cook this onion with fish (even though you may not cook meat and fish together) but the fish may not be eaten with dairy food.
Situation You cut an onion with a meat knife and fry it in a neutral/pareve pan.
StatusThe pan becomes meat, but consult a rabbi for possible leniencies.

Situation You cut an onion with a meat knife and fry it in a dairy pan.
StatusThe pan becomes non-kosher.  If you cook a neutral/pareve food in that pan after 24 hours have passed since the onion was cooked in it, and you ate the pareve food with milk, it is OK b'di'avad but you may not do that l'chatchila.