Chullin 119 - Handles And Protectors
Earlier we saw that there can be light and strict impurity. Light impurity is that of foods: it requires the larger volume of an egg to be transmitted, and it can be transmitted only to other foods. Strict impurity is that of dead meat ( nevelah ): it requires a smaller volume of an olive to be transmitted, and it can make ritually impure even people and utensils.
Furthermore, impurity can be transmitted not only through direct contact with the item, but also through contact with its handle or its protector. A handle is an appendage that can be used to grasp the item, such as the stem of a fruit. A protector is an appendage that protects the item, such as the peel of a fruit.
Thus, if the source of impurity touches the stem or peel of a susceptible fruit, impurity is delivered to the fruit via its attached handle or protector, even though they are not food and would not be susceptible to impurity in their own right. Conversely, if the stem or peel of an impure fruit touches a susceptible item, the impurity is delivered to the item via the fruit's handle or protector.
Art: Ignace Henri Jean Fantin-Latour - Still Life, Hyacinths and Fruit