kashrut

Question

Rabbi Perhaps I didn't ask my question of 3/27 correctly so please clarify. A box of donuts that has a K and no obviously unkosher ingredients like lard can be eaten according to your reply. But, how do you know that all ingredients like mono and di-glycerides, etc. are kosher? How can a lay person know all possible kosher ingredients? What is your rationale for allowing eating these? Also are mints with stearates(magnesium) ok to eat?