Made small batch of strawberry jam this week. I make small quantities of jam at a time which is quick and easy and often do it while cooking tea. I get the strawberries when their on special. I use 2-4 punets (500g-1kg). The ratio of sugar to fruit is equal but I reduce the sugar. I’m making small batches that get consumed within a few months . The sugar helps set it as well as acting as a preservative. To this you add lemon and Pectin as these do help the jam set. This year I’ve planted more strawberrie plants and plan to grow enough to make my own jam!