I have often wondered what the shelf life of pectin is and even though I don't have a definitive answer to that question, I do know that pectin can go bad. By 'bad', I mean that it'll get old and lose it's jelling power. I know this for a fact.
I got some bulk pectin on sale last winter for 1/2 price and I couldn't pass it up. When I went to use it this year, I noticed it had yellowed some and had some clumpies in it. I ignored it and used it anyway and batch after batch of jam came out too thin. I finally threw the old pectin away and opened a new batch, which, of course, works beautifully and has made fantastically jelled jam.
So, now you know. Pectin can go bad. If it's yellowed or has started to clump, try one small batch. If it isn't as thick as you like, then do yourself a favor - pitch the old stuff and get some new.
[And don't feel bad. It's only pectin.]
