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Prepare the grapefruit
Wash the grapefruit thoroughly. Cut into chunks, keeping the peel and pith but removing all visible seeds, as these can add harsh bitterness. -
Cook the fruit
Place the grapefruit pieces into a large saucepan with the water and lemon juice. Bring slowly to the boil, then reduce to a steady simmer. Cook for 40 minutes until the peel is very soft and the liquid is well flavoured. -
Strain the juice
Pour the mixture into a jelly bag or a muslin-lined sieve set over a bowl. Leave to drip for at least 4 hours or overnight. Do not squeeze the fruit, as this will cloud the jelly. -
Measure and sweeten
Measure the strained juice. For every 600 ml of juice, add 450 g granulated sugar. Transfer both to a clean saucepan. -
Boil to setting point
Heat gently, stirring until the sugar dissolves completely. Increase the heat and boil rapidly for 10 to 12 minutes. Test for set using the chilled plate test. The jelly is ready when it wrinkles lightly when pushed. -
Jar the jelly
Remove from the heat and skim off any surface foam. Pour into warm sterilised jars and seal immediately.
Practical Tips
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White grapefruit produces a firmer set than pink varieties.
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The bitterness mellows noticeably after a few weeks of storage.
Serving Suggestions
Serve with buttered toast, spoon alongside roast chicken, or pair with soft cheeses.
Storage and Reheating
Store sealed jars in a cool, dark place for up to 10 months. Once opened, refrigerate and use within 3 weeks.