Glicerin

Question

Dear Rabbi, In reading the Q&A section of our website, I have been happy to learn that many popular foods are kosher. However, many of them contain glicerin. This is especially true of chewing gum and candy. How can we know that the glicerin used is kosher? My understanding is that there are two kinds of glicerin: animal and vegetable. So how can we know which one is being used for us to be sure that the food is indeed kosher? Another question: are Jolly Ranchers candies all kosher? Thank you very much.