Sterilize the jam jars and lids by boiling them in water for 10 minutes. Remove and let dry before use.
Wash the rhubarb and cut it into roughly 2 cm pieces. Place in a pot with the sugar, lemon zest, lemon juice, orange zest, and orange juice.
Heat over medium heat, stirring occasionally to ensure even heating. Once the rhubarb releases juice and the mixture begins to boil, reduce to low heat and simmer gently for 15 minutes.
Pour the rhubarb and juices into a fine mesh strainer. Gently stir to allow as much juice to pass through as possible.
Pour the strained juice back into the pot and bring to a medium-high heat until the temperature reaches 105°C (221°F).
Return the strained rhubarb solids to the pot. Heat and stir. Once the jam comes to a boil again, cook for about 2 more minutes and then remove from heat.
While still hot, pour the jam into the prepared jars. Seal tightly and turn upside down to cool.
It’s best to use heat-resistant glass jars for storing the jam. Lids with extra sealing rings or seals can help extend shelf life before opening.
This recipe already uses a very small amount of sugar. Reducing the sugar further would make the jam too sour. A higher sugar concentration also helps thicken the texture and prolong shelf life.
The method of separating and heating the juice can be applied to other jam recipes. It significantly reduces the total cooking time.
Heating to 105°C (221°F) helps evaporate excess water, increase sugar concentration, and activate pectin for the ideal jam consistency.
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