Question: Help with homemade syrup?

Couple of questions actually. Trying to keep it natural, why does everyone else..Aunt Jamima, Log Cabin, etc..use a bunch of preservatives? Do you need to have those in order to have a 1-2 year shelf life? Should it be kept in the fridge once it is opened? Can you use natural acids such as cream of tarter, lemon or brown sugar to keep the sugar from crystallizing? Once it is unsealed (opened) will it cut down on the shelf life? We are trying to make homemade syrup and market it at a natural food store. We are using a flavored water base if that is any help. Any thoughts and suggestions, KNOWLEDGE, would be so very helpful. Thank you.