Strawberry jam from a row that gave 2.3 kilograms, in two small batches
The strawberry row is five metres long and in its third year, and this June it gave 2.3 kilograms over two weeks, picked every other evening into a colander. Strawberries are low in pectin and low in acid and they go to mush if you look at them, so this is the hardest common jam to set properly and the one I have made most often badly. This year I made two batches of just over a kilogram each rather than one big one, because a small batch boils faster and the fruit spends less time cooking.
Each batch: 1.1 kilograms of hulled fruit, the biggest berries halved, layered with 1 kilogram of sugar in a bowl and left for four hours until the sugar had dissolved into the juice. This stops the fruit breaking up as much in the pan. Then into the pan with the juice of two lemons, brought up slowly, and boiled hard. The first batch took 11 minutes to a saucer-test set at a thermometer reading of 105; the second, from fruit picked three days later and slightly riper, took 13 minutes.
Scum was the main nuisance. Strawberries throw a thick pinkish foam that has to be skimmed or it sets as a cloudy layer in the jar. A knob of butter the size of a hazelnut stirred in at the end dispersed most of it, and I skimmed the rest. Five jars from each batch, ten in total, 340 grams each, with the fruit distributed evenly rather than floating at the top, which I put down to letting the jam stand for five minutes off the heat before potting.
The set is soft, deliberately. A strawberry jam that stands up on a spoon has been boiled too long and tastes of toffee; this one spreads easily, holds on bread without running, and is very red. The first batch is slightly softer than the second and both are fine. I had one jar that failed to seal because of a chip in the rim, and that went straight into the fridge and was gone in a week.
For next year: pick in the morning rather than the evening if the weather is hot, because berries picked warm went soft faster; and buy more lemons, because I ran out and had to borrow one.