It is only sugar and fruit and water - it will last forever. Might get gummy with age as water evaporates - especially in a frost free fridge. But I'm pretty sure it will be gone before then!
I went to the site suggested by jennye and from there to another site - seems they use an ice cream machine. Plus they juice their fruit and add sugar to that. I didn't go any further nor read it in depth but it certainly would be a good place for you to start! I'm sure you will find some good tips and ideas.
Let us all know what kind you make and how it goes!