First atempt at strawberry jam this year and the recipe I used called for lemon juice to help it set, think it was a Delia recipe. Spent ages checking that it was setting using the wrinkle test thing and have now ended up with some that's too set (thought the problem was always the other way round with strawberries!). Have given my mum's old jam thermometer a new home in the hope that I'll be better next time at guessing when it will set from checking the temperature. Tastes nice though and warm toast softens it up a treat!