Cinnamon Basics

All cinnamon contains a certain percentage of coumarin, which is a substance that can lead to temporary liver and kidney damage.  Though this damage usually occurs during the holiday season when we tend to eat a lot of cinnamon, some people like to cook with cinnamon on a regular basis.  If this is the case, it is definitely a good idea to understand the different types of cinnamon since not all types of cinnamon contain large amounts of couramin.

Cassia vs Ceylon
The two main types of cinnamon are cassia and ceylon.  Cassia cinnamon, which is from China and Vietnam, generally contains a large amount of couramin whereas, ceylon cinnamon, from Sri Lanka, has a minimal amount.  Unfortunately, there are no laws in the U.S. which require companies to make the distinction between the two types of cinnamon in product labels.  In fact, since cassia cinnamon is generally a lot less expensive, this represents the majority of cinnamon available on the market in the U.S.  

Where to Find Ceylon Cinnamon 
Finding ceylon cinnamon in regular grocery stores may not always be possible; however, your local coop or health food store may have it and you can always find ceylon cinnamon on-line.
Cinnamon Sticks: If you are looking for ceylon cinnamon, you can generally find the ceylon cinnamon sticks on-line or in the bulk spices section at Whole Foods.  
Ground Cinnamon: The ground ceylon cinnamon can be purchased on-line at a variety of sites including Olive Nation.  If you have any trouble finding ground cinnamon or you need it right away, you can always make it on your own.  Just take a couple of ceylon cinnamon sticks and put them in a coffee bean blender.  Blend until the sticks turn into a fine cinnamon powder.  If you use this method, I recommend storing the ground cinnamon in the refrigerator in order to preserve the flavor.
Cinnamon Extract:  I have not yet found a cinnamon extract that is specifically labeled ceylon cinnamon.  However, it's been a while since, I've looked so it is worth googling it to see if anything new has come up.  However, if you are like me, you may consider making your own extract.  This process is quite easy.  The only drawback is that it takes a few months before the extract is ready.  

Ceylon Cinnamon Extract Recipe

How to tell the difference between cassia and ceylon?
Cassia is darker in color and has a fuzzy texture.
Ceylon cinnamon is a light brown color and has a dry paper like texture. Ground cinnamon can generally be distinguished by the shade of brown.  Cassia is a dark red-ish color and ceylon is a lighter brown or orange-ish color.

Link to very informative article on the benefits and dangers of cinnamon.