Terumot, Chapter Ten, Mishnah One
This chapter deals with terumah that has been placed together in a dish with hullin after it has been cooked, and with whether the whole mixture has to be treated like terumah.
An onion [of terumah] was placed into lentils:
1) If the onion was whole, it is permissible;
2) But if [the onion] had been cut up, [it is forbidden if it] imparts a flavor.
3) In the case of other dishes, whether the onion is whole or cut up [it is forbidden] if it imparts a flavor.
4) Rabbi Judah permits it in the case of mashed fish, because it is used only to remove the unpleasant flavor.
Section one: In this mishnah one of the two characters, the onion or the lentils, is terumah and the other is hullin. If the onion is whole it wont impart its taste to the lentils, nor will the lentils impart their taste to the onion. Lentils dont have a lot of taste nor do they easily take on the taste of things cooked with them. Since one cannot taste the other both retain their former status and whichever one was hullin is still permitted to the non-priest.
Section two: If the onion had been cut up then it will impart its taste to the lentils if there is sufficient quantity of onion, and if there is sufficient quantity of lentils, they will impart their taste to the cut-up onion. Therefore, if the terumah food imparts its taste to the non-terumah food, the non-terumah food must be treated like terumah and it can be eaten only by a priest. The priest should taste the non-terumah food and if it has the taste of the terumah food, then only the priest can keep eating it.
Section three: The previous was true with regard to lentils which dont have a strong taste and are not so susceptible to the taste of the onion. When it comes to other dishes, it doesnt matter whether the onion was cut up or not, the dish is prohibited if the onion can be tasted.
Section four: Rabbi Judah says that if a terumah onion was put into a mixture of mashed up fish, a mixture which has a bad smell, the fish remain permitted to a non-priest because they were put there not to give taste but to get rid of the bad smell.