6 large limes (or 8 small)
1 kg sugar
4 cups water
1 tablespoon citric or tartaric acid
Finely grate the lime rind, taking care not to include any of the pith. Squeeze the juice from the limes and set aside.
Combine the lime rind, citric or tartaric acid, sugar and water and heat until the sugar is dissolved. Add the reserved lime juice and mix through. Leave to stand until the mixture is cool (or overnight). Strain the mixture through a fine sieve.
Pour into sterilised bottles and seal.