Not all cinnamon is alike, although in its ground form, it may be difficult to tell the difference between two common varieties, cassia and Ceylon. With stick cinnamon, you can see differences in the bark's roll pattern and texture. Other differences could potentially affect your health: the two types of cinnamon vary in their levels of coumarin, an anticoagulant that may pose a health risk if consumed in large amounts regularly. Cassia will have a higher level of this substance, whereas coumarin content in Ceylon cinnamon is comparatively low.
Check the bark. Ceylon cinnamon has a thinner bark than cassia cinnamon and is composed of multiple layers. Cassia is essentially one thick piece of bark that curls inward on both ends into a hollow tube.
Observe the color. Look for a darker reddish brown color in cassia, as compared to a lighter brown in the Ceylon cinnamon. Taste the cinnamon, if you can. Cassia cinnamon has a certain hotness or spiciness, whereas Ceylon cinnamon will have a more delicate taste.
Feel the texture. Compare the bark of the two types of cinnamon. Ceylon cinnamon's bark will be smoother than the rougher cassia bark. Note the relative hardness of the latter compared to the thin pliable layers of the Ceylon cinnamon. You will be able to grind the latter in a coffee grinder; doing so for cassia is not recommended.
Find out the origins of the product. Check the label on the product, in particular if the cinnamon is ground, because from the ground spice alone it may not be evident which type of cinnamon you are dealing with. Look for signs that the cinnamon came from China or Vietnam, which indicates that it is cassia. See whether the origin is Sri Lanka, or Ceylon, in which case you are working with "true cinnamon," otherwise known as Cinnamomum Zeylanicum.