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Hi all jam lovers

I wonder if any of you can tell me the science behind jam... what I make these days and call 'jam' is basically a whole bunch of fruit (fresh or frozen) with about a handful of sugar, no more, boil it up for a bit and then use it over the next few days/week or so. Completely unscientific and unmeasured.

What I want to know is how to make jam that will keep for a long time but not necessarily contain a tonne of sugar, and definitely not turn out like jelly - I like my jam runny!

Is there a science or is it trial and error? Will less sugar mean it goes mouldy even if it's stored well?

Share your jam joys and disasters :)

If you fill it boiling hot into screwtop jars, it should not need all that sugar. I bottle fruit in those jars without any sugar at all, and they keep for years. I do sterilise the bottles after filling, though (boil for half an hour or so in pan filled with water to about 1cm under tops).

I make jam with equal measures of fruit and sugar (give or take) That's the way I like it - I do follow recipies, sometimes. I usually add spices or whisky as a flavour too.

Sterilising is essential though, and putting lids on while contents are still hot - I put the jam in while both jars and jam is really hot, then I wait until I can comfortably hold the jar to tighten the lid.

Sterilise by -

Washing jars in hot water (or dishwasher)and dry out in an oven at 100oC
Or half fill clean jars with water and microwave for 10 mins

ina wrote:If you fill it boiling hot into screwtop jars, it should not need all that sugar. I bottle fruit in those jars without any sugar at all, and they keep for years. I do sterilise the bottles after filling, though (boil for half an hour or so in pan filled with water to about 1cm under tops).

Ina - do you bottle fresh fruit (ie. un-cooked, no other ingredients), then boil the jars in water? lids on or off?

I have never seen that done.

This might sound like a daft question but can you store tomatoes like that - I go through tonnes of tinned tomatoes, but if I can successfully jar my own that would be great.

I'm with Annpan here.. I use same volume of sugar too fruit pulp/jelly etc

can't tell you the science bit - the sugar pectiin acid levels are about it setting not keeping.

high sugar levels do help it keep tho

but the best thing is the be ultra clean. I steralyse by filling the jars with boiling water right to the very top whilst the jam is making, and the lids go in a jug with yet more boiling water. it works for me

also i keep jam in the fridge when there is space.. might as well make full use of having the fridge on.

Annpan wrote: Ina - do you bottle fresh fruit (ie. un-cooked, no other ingredients), then boil the jars in water? lids on or off?

Depends on what I do: rhubarb and red currants I fill in raw, fill to about 1cm from top with fruitjuice (preferably hot), screw lids on, then in water and sterilise. Apples I usually cook to mush first; they don't need so long to sterilise then. The times needed depend a bit on what you are doing, and how big the jar is.

I always check after I've taken them out that the lids are on properly.

Oh, and when I make jam, I turn the jars upside down for cooling - can't remember where I read that, but it's supposed to make them keep even longer! Screw the lids on as soon as possible, too - hold the jars with a cloth to prevent burning your fingers. I've tried using less sugar, too, but I find it doesn't really taste like jam then...

You can heat treat the jam after it's been put in jars. Oded Schwartz gives a good description of how to do it in his book on preserving. I'll try and remember to bring the book in tomorrow. If I forget to post the instuctions will someone please PM me to remind me (I'm abit forgetful, goodness knows what I'll be like when I get old )

All very interesting! So it's more about heat-sealing it and sterilisation than quantity of sugar... that's good!

I'm also interested in finding out how to preserve other things, so it's fab to know raw ingredients can also be used in this way, as I'm not keen on pickling!

Anyone got any good preserve recipes/ideas?