Microbiologist help - 20 year old jam!

[Dave2002]

I found a jar of jam on a shelf today - indeed one of many. This one turns out to be about 20 years old. The seal was still OK - I had to heat the top to get the lid off. The contents didn't smell too bad, and indeed still had a recognisable smell - and there was no sign of mould which one would get with opened jars.

I suppose the most sensible thing to do is to dump the contents, but I just wonder how long preserves can be kept in hermetically sealed jars without actually becoming dangerous to eat. I have read that canned food can last for a very long while - though the flavours may go off.

According to various food sites, jams and preserves should normally not be eaten after 1-2 years after their sell by/use by date.

[oddoneout]

If the seal is intact and the lid concave then it's difficult to see that there would be a problem, other than loss of quality(texture, flavour, colour). Traditional(high sugar) jams were intended to last, and also traditionally without the benefit of vacuum seals/metal lids - an old cookery book I have refers to tying down as a sealing method(using paper of various sorts) and mention is also made of mutton fat and pig's bladder for sealing purposes. If anything had been festering or growing over that length of time I suspect you would have known(heard?!) about it, and jars sealed with the cellophane and rubber band method would have lost their covering long since and acquired mould growth, thus answering the question for you.