If you're still not convinced about just how easy it is to make gorgeous jams, follow Delia's 10-point plan for success every time!
Sugar has a hardening effect, so tough-skinned fruits should always be simmered before the sugar is added to the pan.
Conversely, soft-skinned fruits, such as strawberries, which tend to disintegrate when cooked, should be soaked in sugar first, to harden them and help keep the fruit whole in the finished jam.
The sugar should be completely dissolved before the jam reaches the boil, otherwise it will be difficult to set and the finished jam will be sugary. To test if the sugar is dissolved, dip a wooden spoon in, turn it over and if no sugar crystals are visible in the liquid that coats the back of the spoon, it has indeed dissolved. (To be quite sure, stir well and repeat this test a couple of times.) To speed up the dissolving process, you can warm the sugar in a bowl in the oven before adding it.
Don’t try to make too large a quantity of jam in one go. It will take far too long to come to the boil, and then will not boil rapidly enough to produce a good set.
How to test for a set: at the same time as you begin cooking the fruit, place three or four saucers in the freezing compartment of the fridge. When you have boiled the jam for the given time, remove the pan from the heat and place a teaspoonful of the jam on to one of the chilled saucers. Let it cool back in the fridge, then push it with your finger: if a crinkly skin has formed on the jam, then it has set. It if hasn’t continue to boil for another 5 minutes, then do another test.
Don’t worry about any scum that rises to the surface while the jam is boiling – if you keep skimming it off, you’ll finish with no jam at all! Instead, wait until you have a set, then remove the jam from the heat and stir in a small lump of butter, which will disperse the scum.
Once the jam has set, leave it to settle for 15 minutes or so – particularly with jam containing whole fruit, such as strawberry or damson, or chunky marmalade – to prevent the fruit from rising to the top when it’s poured into the jar. Then pour into clean, dry, hot jars, filling them as near to the top as possible. Straightaway, place a waxed disc over the surface, then seal with a lid. Wipe the jars with a warm, damp cloth.
Don’t put the labels on until the jam is cold – otherwise the heat will prevent them sticking properly and they’ll fall off for sure.
Store in a cool, dry and preferably dark place. Too much light is not good for storage, while a damp or steamy atmosphere can cause mould to develop on the surface of the jam.
If things go wrong: if the jam hasn’t set after cooling and potting, tip it all back into the pan and boil again, adding the juice of a small lemon; if mould develops on the surface of jam in a jar, remove it with a spoon, along with about half an inch (1 cm) of the jam underneath – rest assured, the rest of the jam will not be affected – and place a waxed disc dipped in brandy on top.