There's a simple secret to making blackberry jam without the benefit of a jam thermometer. Country Life reader Sam Dixon explains how.

I developed this blackberry jam from a recipe for raspberry preserve that I already had. The fruits contain similar amounts of natural pectin and so need the same amount of help to thicken.

You can make a big batch and pour it into jars, but I usually just make a small amount to fill a sponge cake or for a special brunch.

blackberry jam

Method

1. Weigh out twice as many blackberries to caster sugar and place in a very large pan.

2. Add a couple of tablespoons of lemon juice to help the preserve thicken.

3. Bring to boil and then let simmer without stirring for 20 minutes.

4. Do the fridge test. Dollop a little of the jam liquid on a cold plate and put in fridge for five minutes. If it sets then it’s ready. If not, keep cooking and testing every five minutes.

5. If you’re using jars, rinse them with hot soapy water and dry in a hot oven while preparing your jam. When it’s ready, pour in and screw the lids on tightly.