Sophie 378's guide to jam-making
Preparation
When the fruit is in season, buy it by the crate and make dozens of pots of jam. If you made it well, it keeps for years (I recently opened a jar labelled Apricot 1995; it's still delicious). A good jam is recognised by the firm but not stiff set, the deep color, the fresh taste, and the good keeping properties. Home-made jam is a wonderful gift, especially if you've grown and/or picked the fruit yourself. Strawberry, raspberry, apricot, bullace, blackcurrant, blackberry, loganberry, damson, greengage, quince, etc - most fruits can be made into delicious jam. It's not just spread on bread for breakfast, either: in Bakewell tart, trifle, over ice-cream, in cakes - jam is good.
Collect jars whenever possible. Pretty much any glass jar with a screw-top lid, or a clip-on lid like coffee powder, can be used. Jam, honey, olives in brine, pickled cucumbers, pasta sauce, curry paste, coffee, etc. When they're empty of the original contents, soak them until all the label stuff comes off. Wash and dry, and leave with the lid on for a few days; if it smells after that, wash it again. Use jars with metal lids for jam, and plastic lids for pickles and chutneys: the stronger acid in those can corrode the lids.
Making the jam
1A If the fruit is excellent quality, remove anything you don't want in the jam (seeds, stalks, stones etc), wash and chop it and leave it in a bowl with 75-100% of the same weight in sugar (depends on the acidity of the fruit, and how sugary you like your jam) in the fridge overnight.
OR
1B If it's not excellent quality, (or if you just want a homogenous jam rather than with lumps of fruit) just remove yucky bits, rinse, and simmer it gently until soft. Then, bash it through a non-metal sieve: this will catch stones, stalks, skin, etc. Measure out the pulp produced; use a pound of sugar per pint of pulp (75% of the mass of the pulp).
2 For both, you should then have a mix of fruit and sugar. Put them into the biggest saucepan you can sensibly use - it should half-fill it at the most. Warm gently, stirring occasionally, until
all the sugar has dissolved. If you can hear crystals scratching, or you can see them, it's not ready.
3 Meanwhile, get your jars ready - at least twice as many as you think you'll need. It may be maddening to have to get them all ready and then have some left over; but that is nothing to having potted most of the jam and then you've no jars left. Wash them again, and then put into a hot oven for about half an hour to sterilise. Don't put the lids in; the rubber seals will deteriorate. Put your jam funnel (if you've got one) and metal ladle in too. Leave them in the oven until you're ready.
Also, put a small clean plate into the fridge.
4 Once that's ready, and the sugar has dissolved, bring the jam to a full rolling boil, and keep it there. Do not stir once the sugar has dissolved. Boil it until a small spoonfull of the jam sets on the cold plate (this may take a minute or so) - it wrinkles up in a mound ahead of your finger if you poke it, rather than just splashing out of the way. This may take only five minutes for wild strawberries, or half an hour for damsons. Some soft fruits are notoriously bad setters - strawberries, for instance - so you may need to add pectin (can be bought in jars or as powdered sachets).
4A (If you're doing a jam with lumps of fruit rather than homogenised gloop, there is a sneaky trick you can use: once the fruit is really soft, pour the whole lot through a metal sieve or fine colander to extract the fruit. Let most of the syrup goo drip out, then boil it up until it's really ready to set, leaving the fruit out. This gives a better texture and appearance, as the syrup is ready to set without the fruit being boiled until it's a dark pulp. When the syrup is ready, put the fruit back in, stir it up briefly, and bring back to the boil to re-sterilise. Then go to the next paragraph.)
5 Leave the jam to cool until you can touch the pan without burning yourself. (This will prevent the fruit rising to the top, as well as making the next job more sticky than dangerous.) Stir in the pectin, if needed. Take your jars out of the oven, and use the ladle and/or jam funnel to transfer it to the jars. Fill each jar up to within a few millimeters of the brim: the smaller the airspace, the less likely it is to go mouldy. Lid each jar as you finish it.
6 When you've filled all the jars and lidded them, allow them to cool. Soak your pan and the utensils you've used as soon as possible, or the stickiness will just get worse. When the jars are cool, tighten the lids again, wash any splashes of jam off, and label them (eg Damson 12 Sept 2006).
There! You've made jam. Not so difficult, was it? You'll get better with practice.
Edit Added numbers to paragraphs for clarification, and 4a.
thanks for sharing 
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