I posted a question below about how to use hazelnut butter. Thank you very much to those that responded, I'll definitely try your suggestions. One other question I had was about the shelf life of hazelnut and other nut butters, if the jars are unopened. Can I use old jars? And, once opened, how long can I keep them in the refrigerator? Will I simply know by the smell indicating rancidness? Is there any danger in using old jars? Thanks for any help.