How can you tell if beef jerky is no longer good? We have some in a sealed (vacuum) pack.?

This is Amish made beef jerky that has never been opened. It smells great, tastes good - it looks really dry and has some sort of sparkle to it? The only thing really is that it looks dry. There is no mold or anything like that but we are just wanting to find anything to help us figure it out. Please no smart alec answers... we really are trying to figure this out. Thank you to everyone who tries to help!