Commentary for Avodah Zarah 78:12

As we explained in the previous mishnah, the concern with milk is that the non-Jew might mix milk which comes from a kosher animal with milk that comes from a non-kosher animal (such as a camel). If the Jew is watching over the non-Jew we have no such concern and the milk is therefore permitted. Mixing foreign substances with honey would spoil the honey. Therefore we can assume that the non-Jew did not put anything into the honey and it is permitted. Even though some grape juice may be dripping from the cluster of grapes, we are not concerned that the non-Jew used this juice in idol worship and it would be forbidden. The mishnah also notes that the liquid that comes out of grapes is not the type of liquid which makes a food susceptible to impurities. As we have learned before (Eduyoth 4:6) food cannot become impure until it is made wet by seven types of liquids. Grape juice is not one of them. Preserved foods into which it is not customary to put wine or vinegar are permitted. If one can see that the fish in the brine is actually herring, it is permitted, unlike the minced fish which was discussed above. In the previous mishnah we learned that it was forbidden to eat pieces of the asa foetida, since the same knife used to cut this plant might have been used to cut non-kosher food. In this mishnah we learn that since they don’t cut the leaves of the as foetida with this type of knife, it is permitted. Olives that have been rolled out into cakes are permitted, since no wine is used in them. According to Rabbi Yose, if the olives have become so soft that the pits fall out, wine might have been put on them to soften them. Therefore, they are forbidden. Some types of locusts are kosher. When a seller sells them, he brings them from his storehouse and puts them in a small basket, onto which he mixes a little wine. Due to the addition of this wine, locusts that come from this basket are forbidden. The locusts that come from the storehouse are permitted since the wine has not yet been put upon them.
The mishnah points out that the same is true with regards to terumah. If a kohen sells locusts from the little basket, we must suspect that he has dripped wine on them, and that the wine might be terumah, which is strictly forbidden to non-priests. If, however, the locusts come from storage, we can be sure that there is no terumah-wine mixed in with them.