So when I say Cinnamon here I mean cassia. For most people they are the same thing, but in truth original ceylon cinnamon has a very different flavor. I'm hoping to get some ceylon in the near future, but it will depend on when Mountain Rose herbs puts in their next order.
Cassia Cinnamon is what most people are accustomed to. It is the bark of the Cinnamomum aromaticum plant. It is the strongest and most fiery of the cinnamon varieties, and is also the most common cinnamon spice in America and Canada. Most cinnamon liqueurs made commercially have a very strong fiery flavor which looses the subtle nuance that the whole bark can bring to a flavor profile. To get this effect many of the least expensive schnapps and liqueurs only use artificial cinnamon to get the fire to the exclusion of everything else. In many cases the initial infusion of cinnamon may be distilled to remove the resins and complex compounds and keep only the most volatile of the cinnamon flavors that will survive the distillation with the alcohol. Cinnamon brings a very strong tannin profile, and if left in the liquor long enough will actually thicken the infusion with no simple syrup at all because of the resins in the cinnamon bark. So be very careful about your infusion times. While the cinnamon tannin can be very nice and I know several people who enjoy it, it can also get out of hand, so test regularly and stop when the tannins are at the level you enjoy them.
Ratios: Because the strength of stick cinnamon can vary so much I recommend going very heavy with your intial infusion and if it is stronger than you want then you can add additional pure rum to the mixture and reach the flavor balance you are going for. I would break up 4-6 sticks of cinnamon (depending on size) for a ball far sized infusion. More like 10 sticks of cinnamon for a full bottle. The reason I recommend breaking the sticks is so you don't have to use more alcohol than necessary to cover them in a ball jar. If you are just putting the sticks into a full bottle of rum then breaking them is not necessary. You will have a delightful quality infusion in 24 hours. If you want a strong tannin profile you can go as far as you want without any bitter or unpleasant side flavors. Just be aware that the tannin profile of this infusion can become very intense.
Flavor Profile: You will have fire, and wood, and earth. This is a very grounding flavor despite its fiery front. It pairs very well with coffee, other spices, nut liqueurs, and some fruits as well. Left just as in infusion it is also delightful in many desserts. Though I recommend a brief low tannin infusion for dessert applications.