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squirrelydan76
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PdfSterilise jars in a 120°C oven and chill 2–3 small plates in the freezer for the set test.
Put the rhubarb and lemon juice in a heavy-based saucepan over medium heat. Cook, stirring, until the rhubarb collapses and releases its juice. No added water needed.
Add the strawberries, crush roughly with a potato masher leaving some chunks, and simmer until it looks jammy rather than watery. This is the key step — you're concentrating the fruit before the sugar goes in so the later hard-boil stays short.
In a bowl, whisk the pectin thoroughly through the sugar until evenly dispersed. This prevents the pectin clumping when it hits the hot fruit.
Tip the pectin-sugar mix into the reduced fruit. Stir constantly over medium heat until fully dissolved — do not let it boil yet, or you risk a grainy set.
Bring to a rolling boil that can't be stirred down and hold for ~2 minutes, aiming for 104–105°C. Trust the thermometer and the plate test over the clock — over-boiling HM pectin degrades the gel.
Take off the heat. Drop a teaspoon onto a frozen plate, wait 30 seconds, then push with a finger. If it wrinkles, it's set. If not, boil another minute and retest.
Skim any foam, rest 5 minutes so fruit suspends evenly, then ladle into hot sterilised jars leaving 5mm headspace. Seal and invert for 5 minutes.