Why Forced Rhubarb Makes the Finest Jam

If you grow your own or buy from a farm shop, the first sticks of forced rhubarb in late winter are worth setting aside for the preserving pan. Grown in darkened sheds and picked by candlelight, forced rhubarb is tender, sherbet-sharp and startlingly pink. It also happens to be one of the poorest fruits for pectin, which is exactly why it needs a little coaxing rather than a hard boil.

Field rhubarb, cut later in spring, is coarser and greener, with more pectin but far less charm. If that is what you have, the jam will still work beautifully, but expect a slightly duller colour and a firmer, more rustic set. Either way, the principle is the same: gentle cooking, plenty of acid, and a soft, spoonable set rather than something you can slice.

Warming the Ginger Properly

Ginger and rhubarb are old friends, but the heat needs handling with care. Raw grated root ginger can taste harsh and slightly soapy in a preserve, so warm it first. Peel about 50g of fresh root ginger, slice it into coins and bruise them with the flat of a knife. Simmer the coins gently with the lemon juice and a splash of water for ten minutes, then strain, keeping the liquid for the pan. You get a rounded, woody warmth instead of a raw bite.

Alternatively, tie the bruised ginger in a square of muslin and leave it bobbing in the pan while the fruit cooks, fishing it out before potting. Ground ginger, a teaspoon or two at most, goes in with the sugar and gives a background hum, but too much turns the jam dusty and brown. My favourite trick is to finish with three balls of stem ginger, finely chopped, plus a tablespoon of the syrup — little nuggets of heat that surprise you on buttered toast.

The Jam Itself

• 1kg forced rhubarb, trimmed weight
• 1kg granulated sugar, or preserving sugar with added pectin
• Juice of 2 lemons
• 50g fresh root ginger, or 2 tsp ground ginger
• 3 balls stem ginger with 1 tbsp syrup (optional)
• A small knob of butter

Cut the rhubarb into 3cm lengths and layer it in a large bowl with the sugar, covering each layer as you go. Leave it overnight, covered, somewhere cool. By morning the sugar will have drawn out a shocking amount of pink juice, and this is the secret to keeping the pieces intact — the fruit barely needs to boil at all.

Tip everything into a preserving pan or a wide, heavy-based saucepan, add the lemon juice and your ginger liquid. Bring it up slowly over a low heat, stirring until every grain of sugar has dissolved; rub a little between your fingers to check. Only then turn up the heat and boil briskly. Fifteen to twenty-five minutes is usually enough. Skim off the foam, stir in the chopped stem ginger and the butter, which helps disperse any remaining scum.

Judging the Set

Put two or three saucers in the freezer before you start. Drop a teaspoon of jam onto a chilled saucer, let it sit for a minute, then push it with your fingertip. If the surface wrinkles, it is ready. A sugar thermometer should read 104–105°C.

Do resist the urge to chase a stiff set. Forced rhubarb will always give you something soft and glossy, and that is the whole point — boil it for too long and the pink fades to a sad brown toffee. If it simply will not come together, a squeeze more lemon juice or a tablespoon of powdered pectin will do the job.

Sterilising and Sealing

Wash your jars in hot soapy water, rinse them well and stand them upside down in a low oven at 140°C for fifteen minutes. Keep them warm until the moment they are filled. A hot dishwasher cycle works too, but fill the jars while they are still steaming. Never pour hot jam into cold jars.

Use a ladle and a jam funnel to fill each jar to within 5mm of the rim, wipe the threads clean with a damp cloth, and screw on the lid straight away. New lids are best; if you are reusing, check for rust and dents and discard any that are doubtful. Label when cold.

Keeping and Using Your Jam

Store the jars in a cool, dark cupboard, where they will keep for up to a year. Once opened, keep them in the fridge. The balance of tart fruit and warm ginger is wonderful rippled through yoghurt or rice pudding, spooned over vanilla ice cream, spread through a plain sponge, or brushed over roast gammon in the last ten minutes of cooking.

Check the jars after a few days for any signs of mould; if you see any, discard the jar rather than scooping it off. Otherwise, write the date on the lid, tuck a jar away for Christmas, and give one to a neighbour who will pretend not to have been waiting for it.