2 kg castor sugar
1 litre water
30g citric acid
30g tartaric acid
juice from 6-8 lemons, strained (300 mls)
finely grated zest from 2 lemons
Heat the sugar and the water in a large saucepan until the sugar completely dissolves.
Add the citric and tartaric acids and stir them to dissolve as well. Let the syrup cool, then add the lemon juice and the zest. Bottle into sterilised jars.