So far I’ve found that vitamin e (tocopherol) is an antioxidant that slows the decay of butter. Also rosemary extractives are being used as natural preservatives. I’m developing this product for eventual sale so while the initial packaging will be airtight, I would still like to have the three month window to allow a slight inventory cushion, shipping time, and time on the shelf in the store. As I research I’m learning that natural only means derived from natural sources, not necessarily processed in a natural manner. Doing more research on sodium benzoate now since most recipes call for a pinch of salt, I’m wondering if I can substitute a salt based preservative. Thanks for the replies friends.