Sophie Hartley
Why Strawberries Need a Little Help
Strawberries are one of the most delightful fruits to grow and one of the most difficult to coax into a jam. They are low in pectin, the natural gelling substance found in abundance in apples, gooseberries and blackcurrants, and they are also relatively low in acid. Without enough of either, you can boil a pan of strawberries and sugar for an hour and still end up with a very expensive strawberry sauce.
The good news is that you do not need a packet of commercial pectin to make a proper, spoonable jam. What you need is a little patience, a little lemon juice, and fruit that is not quite ready to eat out of hand.
Start with Slightly Underripe Fruit
This is the single most important thing you can do. Pectin levels are highest in fruit that is just shy of full ripeness, and they fall sharply as the fruit softens and reddens. If you grow your own, pick a mix — roughly a quarter to a third of the crop should be firm, pale-shouldered berries that are still faintly white at the tip. Use the fully ripe ones in the mix too, for flavour, but let the underripe fruit do the setting work.
If you are buying fruit from a pick-your-own farm or a market stall, ask for a mixture or look for punnets with a few firm berries in them. Soft, dark, deeply perfumed strawberries make beautiful eating and mediocre jam.
- Rinse the fruit briefly and drain well — do not soak it.
- Hull the strawberries and cut large ones in half. Small berries can go in whole.
- Weigh the prepared fruit accurately, as the sugar ratio depends on it.
The Ratio, the Lemon, and the Overnight Rest
For every 1kg of prepared fruit, use 700–750g of granulated or jam sugar. Ordinary granulated sugar is fine here; you are not relying on added pectin, so there is no need for the preserving sugar sold with pectin included. A little more sugar gives a firmer set and better keeping qualities, a little less gives a softer, fruitier jam that will not last as long once opened.
Add the juice of one large lemon per kilogram of fruit — roughly two tablespoons. This is not just for flavour. The acid helps the natural pectin in the fruit to form a gel, and it sharpens the taste of a fruit that can otherwise turn cloying once sugared.
Now do something most recipes skip: layer the fruit and sugar in a large bowl, cover it, and leave it overnight in a cool place. The sugar draws juice out of the berries and the fruit softens without any heat at all. By morning you will have a bowl of glossy fruit swimming in syrup, and the jam will need far less boiling, which means a fresher, brighter flavour.
The Long, Gentle Boil
Tip everything into a wide, heavy-based preserving pan. A wide pan matters more than you might think — the wider the surface, the faster water evaporates and the shorter the boil needs to be. A narrow saucepan will have you stirring for twice as long.
Bring the mixture to the boil slowly, stirring gently until every grain of sugar has dissolved. Test this by dragging the wooden spoon across the base of the pan; if you can feel or hear grit, keep stirring. Once the sugar is fully dissolved, raise the heat and let the jam bubble steadily — not a furious, spitting boil, but a lively, rolling one that keeps the whole surface moving.
Stir often, and skim the pale pink foam from the surface with a slotted spoon as it rises. That foam is air and impurities, and leaving it in gives a cloudy jam. Expect the boil to take anywhere from 15 to 30 minutes, depending on your pan, your fruit and the weather. A damp day means more water to drive off, so allow extra time.
Testing for a Set
Put two or three small saucers in the freezer before you start boiling. When the jam has darkened slightly and thickened, drop a teaspoonful onto a chilled saucer and return it to the freezer for a minute. Push the edge of the blob with your fingertip. If it wrinkles and holds its shape, it is ready. If it slides about like syrup, boil for another five minutes and test again.
If you prefer a thermometer, a setting point of 104–105°C is what you are aiming for. Remember that strawberry jam is meant to be soft. A jam that sets like rubber is over-boiled and will taste cooked rather than fresh.
Potting and Keeping
Warm your clean jars in a low oven while the jam boils, and never fill a cold jar with hot jam. Ladle the jam into the jars through a wide funnel, filling to within about 5mm of the rim, and wipe the threads clean with a damp cloth. Screw on warm, dry lids immediately.
You should hear the lids pop as they cool. Any jar that fails to seal should be kept in the fridge and eaten first. Store the rest in a cool, dark cupboard, where the jam will keep for a year or more. Once opened, refrigerate and use within a few weeks.
Label the jars with the date and, if you like, the variety. Next February, when the rain is running down the kitchen window, a spoonful of that soft, bright, faintly sharp strawberry jam on hot toast is summer, kept.
