Can I eat e.g. a watermelon cut with a treif (non-kosher) knife on a treif cutting board and stored in a treif container?
According to this article by Rabbi Eli Gersten of the OU, there would be two issues:
- The utensils (e.g. knife, cutting board, etc) used may not have been cleaned.
- The knife may appear to be clean, but in reality it has a fatty film which is treif. The only way to clean the knife would be by scouring it with an abrasive substance.
Therefore, he suggests the following:
If a friend offers you a slice of the watermelon that was just cut with a knife, politely decline. You should assume that the knife was previously used to cut a non-kosher bologna sandwich or a wedge of non-kosher cheese. If you feel compelled to eat the slice of apple, scrub it first.
If it is a fruit platter from a supermarket, you may partake of the fruit since you can assume the supermarket has a dedicated knife for fruit platters. Additionally, due to the sheer volume of fruit cut at one time in such a scenario, we regard the knives and surfaces as clean. The same applies to pre-cut watermelon sold in supermarkets; there is no need to trim the edges.
If the fruit platter came from a non-kosher restaurant or caterer, it is questionable whether you may partake of the fruit, since a single order might be prepared with a non-dedicated knife or on a dirty surface or with the chef’s greasy hands. In this case, the fruit will require washing.