Seville orange marmalade calculator

Two methods, two sets of rules

The British whole-fruit method simmers whole Seville oranges until soft, scoops out the flesh and pips into a muslin bag to give up their pectin, shreds the peel, and boils it all with sugar to the setting point. The marmalade is potted hot into hot, sterilised jars and sealed. The calculator scales the ratio from Thane Prince’s BBC Food method and splits more than 1.25 kg of oranges into separate pans, because NCHFP’s advice for every jellied product is that bigger batches often give soft gels. The BBC recipe gives eight 300 ml jars for 1.25 kg of fruit.

The University of Georgia’s orange marmalade, developed in April 2018 and published by the National Center for Home Food Preservation (NCHFP), is tested for boiling-water canning. Each batch takes 4 cups of thinly sliced peel with its white pith, about 2½ to 3 lb of oranges, plus 4 cups of cut-up pulp, 1 cup of thinly sliced lemon, 6 cups of water and 6 cups of sugar. It makes 7 or 8 half-pints, processed 5 minutes at sea level in sterilised jars, or 10 minutes in clean, hot ones. It was developed with navel oranges, and it is the one to use if you want shelf-stable jars by US guidance: USDA and NCHFP do not recommend the open-kettle filling the British method relies on.

When are Seville oranges in season?

Briefly, in January. BBC Food’s buyer’s guide says Seville oranges are sold in the last three weeks of January, and New Covent Garden Market, London’s wholesale fruit and vegetable market, reported them arriving for “their short season” at the start of January 2023. So plan on early to late January each year, and buy a little extra: in BBC Good Food’s marmalade tips, Walter Scott suggests freezing Sevilles to make marmalade later in the year. Outside the season, the tested University of Georgia recipe works with ordinary oranges.

Why marmalade sets, and when it doesn’t

Marmalade is a soft fruit jelly with pieces of peel suspended in it, NCHFP explains, and its set comes mostly from the peel. Seville oranges are much more sour than eating oranges, BBC Food notes, which is where Seville marmalade gets its sharpness. Lemons are among NCHFP’s Group I fruits with plenty of pectin and acid. Oranges themselves are Group II, low in acid or pectin, which is why the tested recipe adds lemon and keeps the pith on.

The set itself is the same as jam: boil hard to 8 °F above the boiling point of water, which is 220 °F (104.4 °C) at sea level, as NCHFP’s citrus marmalade states. Thane Prince notes it can take up to 30 minutes of boiling, so keep testing with a cold saucer or the flake test. The setting point calculator gives the temperature for your altitude.

Worked examples

• 1 kg of Seville oranges, whole-fruit method: simmer in 1.8 litres of water, keep 1.36 litres of the liquid, add 1.2 kg of sugar; expect about 6½ jars of 300 ml (1.92 litres).
• 2 kg of Seville oranges: two pans of 1 kg, each made as above.
• 6 lb (2.7 kg) of navel oranges, tested recipe, 5,000 ft: two batches, 12 cups (2.4 kg) of sugar, 2 large lemons, 14 to 16 half-pints; set at 211 °F (99.4 °C) and process 10 minutes in sterilised jars.

Common mistakes

• Stripping off the pith. NCHFP says to leave all or most of it on the peel.
• Boiling before the sugar dissolves. Stir over a low heat until it has, then boil hard.
• One giant pan. Make one batch at a time.
• Mixing the two methods, such as the British ratio with a guessed processing time. Processing times belong to the tested recipe; the canning time calculator lists them.

Giving jars at New Year? Print labels with the made-on date and storage on the jar sterilising page.