How important is lemon to shelf jam?

Question

I made Raspberry jam with the Surejel stuff, but didn't use any lemon in it.

It will be consumed by Christmas, will it be ok on the shelf for the next 4 months?

Answer 1

Lemon is important with fruits that oxidate quickly (that is to say fruits that tend to turn brown shortly after you peel them).

The acid in the lemon juice slows down this process and prevents further oxidation, so the colors keep natural.

When using raspberry, it contains a good amount of acid by itself and will not oxidate  so it is not critical that you use lemon.  

Answer 2

Your jam may not set properly, due to a pectin to acid imbalance. I've never tried this, but if this is the case, it's repairable. Simply reboil the jam, add the lemon juice, and rebottle.