Rhubarb is one of the first things to pick in the year, and this jam keeps the stalks as soft chunks in a ginger-warm set. It is a quick recipe: the fruit steeps in sugar overnight, then boils for only a few minutes, and jam sugar with added pectin does the setting.

Makes
about 5 x 340g jars
Keeps
up to 12 months unopened in a cool, dark, dry place; once opened, in the fridge for a few weeks to a month or two
Ready to eat
once cool and set
In season
April to early July outdoors; earlier for forced rhubarb

Ingredients

  • 1kg rhubarb stalks, weighed before trimming (forced or maincrop)
  • 900g jam sugar with added pectin
  • 100g crystallised stem ginger, chopped

The proportions rely on jam sugar, so don't swap in ordinary granulated sugar. To make a smaller batch, scale everything down by the same amount.

Method

  1. Wipe the rhubarb stalks, trim off the leaves and the base, and cut the stalks into chunks of about 2 to 2.5cm.
  2. Scatter a layer of sugar over the bottom of a preserving pan, then a layer of rhubarb and ginger.
  3. Repeat the layers until everything is in the pan, finishing with sugar.
  4. Cover the pan and leave it for at least an hour or two, and preferably overnight, so the sugar draws juice from the rhubarb.
  5. Put a few small plates in the fridge for the setting test.
  6. Sterilise the jars so they are dry and still warm when the jam is ready: a hot dishwasher cycle, water above 90°C for 10 minutes, or the oven at 160°C (gas mark 3) for 10 minutes. Check the jar maker's instructions; some (Kilner, for example) advise against the oven for their jars.
  7. Sterilise new lids separately in a pan of hot water, not a hard boil, and keep them out of the oven (Kilner gives 82°C for 10 minutes for its lids and seals). More detail is in sterilising jars.
  8. Heat the pan gently until the sugar has dissolved and the mixture comes to the boil. Stir carefully so you don't crush the rhubarb.
  9. Boil rapidly for 5 to 6 minutes.
  10. Take the pan off the heat and test for setting point. If it hasn't set, boil a little longer and test again.
  11. Once it has set, leave the jam off the heat to stand for 5 minutes.
  12. Pour the jam into the warm sterilised jars, filling to about 6mm from the rim.
  13. Put the new lids on straight away, while the jam is hot, so a vacuum seal forms.
  14. Leave the jars to cool undisturbed, then check each lid has sealed (sterilising jars shows how).
Chunks of rhubarb layered with sugar in a preserving pan, sugar still visible on top before it has drawn out the syrup
The rhubarb stands in the sugar, preferably overnight, so the sugar draws out its juice.

How this jam sets

Rhubarb is low in pectin, the natural gelling agent in fruit, so it needs help to set. Jam sugar has pectin added to it, which supplies what the stalks lack. Gooseberries and currants usually have enough of their own and set with ordinary sugar (more on which crops do in pectin in fruit).

Sugar also keeps the jam: it is the preservative that stops moulds and other microorganisms growing.

Why the rhubarb steeps overnight

Layering the chunks with sugar and leaving them draws the juice out of the rhubarb. When you heat the pan, the fruit cooks in that syrup rather than in its own collapsing flesh, and the chunks stay whole. Stir gently once it's on the heat for the same reason.

Forced or garden rhubarb

Forced rhubarb, grown under cover over a crown, gives pale, tender, pink stalks early in the year and makes a delicate jam; forcing rhubarb explains how. Ordinary maincrop rhubarb from the garden works too. It is sharper, which the ginger suits well.

Pull stalks from April or May. Stop by late June or early July, or take only a few stalks after that, so the plant isn't weakened for next year. That makes rhubarb jam a spring and early-summer job. If the crowns give you more than one batch's worth, dealing with a glut of rhubarb has other ways to use it.

A warning about the leaves

Only the stalks go in the jam. Rhubarb leaves are very high in oxalic acid. They are considered poisonous and should never be eaten. Most of the plant's oxalic acid builds up in the leaves; the stalks you cook don't contain enough to be toxic. Cut the leaves off in the garden or as soon as the stalks come indoors, and keep them out of the pan. Faded leaves can go on the compost heap, because the acid breaks down there.

Testing for a set

Jam sets at around 105°C, and a thermometer in the boiling jam will show when it gets there (about 104 to 105.5°C). Without one, use the wrinkle test: spoon a little jam onto one of the fridge-cold plates, wait a minute, then push it with your finger. If the surface wrinkles, it's ready.

Jars, lids and keeping

Old jam jars can go round again if the glass isn't cracked or chipped, but the lid can't: always fit a new one, because it is the lid that makes the seal. Some jars seal more reliably than others; see jars for preserving.

Date the jars and keep them somewhere cool, dark and dry. Throw out the whole jar if you find mould or a fermented, yeasty or alcohol smell; don't scrape the top off and eat the rest. Lower-sugar jams keep for less time; how long preserves keep gives the figures for other jams and chutneys.

Common questions

Can I use ordinary granulated sugar instead of jam sugar?

Not in this recipe. It relies on the pectin in jam sugar to set in a short boil, because rhubarb has little of its own. If you only have granulated sugar, use a recipe written for it.

Can I make it with less sugar?

No. Never cut the sugar: with less of it the jam loses its full preservative effect, spoils sooner and may not set.

Can I use fresh root ginger or stem ginger in syrup?

Not as a straight swap. The quantities here are for crystallised stem ginger, and other forms bring different amounts of liquid and sugar into the pan.

How long does it keep?

Up to 12 months sealed, in a cool, dark, dry place. Once opened, keep it in the fridge and use it within a few weeks to a month or two.

Can I reuse old jam jars?

Yes, as long as the glass isn't cracked or chipped. Sterilise them like new jars and always fit a new lid.

Sources

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