Posted: 01/10/2014 at 16:54
I always use added pectin with strawberry jam, whether frozen or not. The easiest way is to use Jam sugar, which has pectin in it. Or of course you can use a bottle of Certo.
NB Preserving sugar is not the same as Jam sugar. Preserving sugar has larger crystals giving a 'brighter' set, but it doesn't have added pectin.