Many cheeses in the US are vegetarian, as they use a microbial rennet source. Still, there are places that use animal-derived rennet sources. Products made with animal-derived rennet sources are not vegetarian. Rennet that comes from an animal is from the stomach lining of a slaughtered cow, sheep, or goat. Some places also use rennet derived from slaughtered pigs. So to answer the question that many people have:
Are Kraft singles vegetarian? No, they are not!
Here is the statement from the company regarding the enzymes used in Kraft singles:
"The process of converting milk into cheese is dependent on coagulating through the use of an enzyme. The enzymes in this product are sourced from both microbial fermentations and animal sources. The animal sources are cow, sheep, and goat."
Kraft singles are not vegetarian because they use rennet derived from the stomach's of slaughtered cow, sheep, and goat.
The good news is that today there are many great vegetarian alternatives that are also vegan and readily available in the stores! Check the produce department at nearby mainstream stores. Even places like Walmart, Target, Publix, and other mainstream grocery stores carry vegetarian and vegan cheeses that taste good. Try the different brands to find your favorite, including Chao, Follow Your Heart, and others!