The season for jam-making is just heating up. Non-cooks might wonder why anyone would want to slave away in the kitchen when it's 30 degrees out-side, sweating over a stove while stirring a pot of scalding jam.
People used to make jam as a way of keeping fruit to eat later in the year, when it was no longer in season. I do it because it's fun. I don't mind making preserves in the heat of the summer, because that's when many fruits are available at a reasonable price. Within the past month, I've made three batches of strawberry jam, and I'm eyeing the market stalls on the lookout for fresh apricots, which have an extremely short season. I'm not rushing to make cherry jam, because the season is much longer, but I plan to experiment with lychees and various types of plum, peach and nectarine.
Yes, I could make strawberry jam in December - and it would be much more pleasant to do so, because the kitchen would be cooler. But the payoff wouldn't be as big - the berries at that time of year are not as delicious as summer strawberries, and they'd be expensive. Instead, come winter, I'll be working with citrus fruits, making kumquat confit (cooked in increasingly dense sugar syrups), salted kumquats (to put in soda water to alleviate sore throats) and various types of orange to make marmalade.
For most types of fruit, I go by the general guideline of four parts fruit to three parts sugar, by weight, although it depends on the sweetness and ripeness of the fruit. I rarely add commercial pectin, so my preserves tend to be very softly set compared with the jams and jellies found in supermarkets. An alternative to commercial pectin is adding home-made apple jelly (the fruit is cooked with the skins and seeds, both of which are high in pectin), or adding a little unripe fruit (also high in pectin) to help the preserves set.
With soft fruits and berries, I mix them with the sugar, let the ingredients sit overnight and stir frequently; this sucks the liquid out of the fruit and helps to dissolve the sugar. Strain the fruit in a colander set over the saucepan, to separate the juice from the fruit. Simmer the liquid to reduce it slightly before adding the solid ingredients to the pan: this reduces the cooking time of the fruit itself, so the preserves have a 'fresher' taste. For all types of fruit preserves, you need to simmer off a sufficient amount of excess water, because if you don't, the jam will grow mould.
It's best to cook most types of jam as quickly as possible, to preserve the taste. Many avid jam-makers swear by cooking the preserves in unlined copper pans that are wider than they are deep. Copper is an excellent conductor of heat, so the preserves cook faster, and the large surface area means quicker evaporation of the liquid; the copper is also said to have a chemical reaction with the acid in the fruit, making it 'set' better. I wouldn't know because I've never used one (they are very expensive), although it's on my wish list. (You need to macerate the fruit with sugar before putting it in the copper preserving kettle, which shouldn't be used for very acidic ingredients.) Instead, I use my largest pan, which can cook about a kilo of fruit in one batch.
If you want to can the jam properly, so the jars can sit on the shelf without going bad, you need to use canning jars that create suction when heated, so the preserves stay in an anaerobic environment. Wash the jars, rinse them well then fill them with boiling water to sterilise them (also sterilise the lids), before leaving them upside down to air-dry. After putting the hot preserves in the jars and sealing them with the lids, boil them in a water bath - a large pan that's filled with enough water to submerge the jars. (To prevent the jars from coming into direct contact with the bottom of the pan, which might crack the glass, put a kitchen cloth on the base). Bring the water to a boil, then lower the heat and simmer for 15 minutes, making sure the jars stay submerged. Remove the jars from the water bath and let them cool. If you want to skip the water-bath step, store the jars in the fridge.