>>1861057i've always just winged it, cook the berries until they're soft, then add enough sugar to taste. Then add lemon juice until it starts to thicken, but before it becomes too sour. There's a certain pH it has to hit to start jelling but best way to describe it is that it's tart but not sour. When it starts to jel, some of the sugar gets used up so you can add more in the process.
>online recipes seem hit or missfollow these guys they are legit
https://nchfp.uga.edu/how/can_07/jam_without_pectin.html 