I make sure to always include vitamin E oil in my oil and butter mixes. I read somewhere that it could help preserve the life. However since I'm not adding water to it, I don't stress about preserving it. I assume that it will last until the expiration date of the oils/butters/herbs. I make sure to not dip my fingers in my buttercream and instead keep a plastic spoon nearby to dip out what I need. This makes me feel better about not transferring moisture from my fingers into the butter.