Berries (with the stalks, washed and dried) – weigh the amount you have
Water – multiply berries by 0.42
Sugar – multiply juice quantity by 0.6
Start by making the juice. Put the berries with the water into a pan and boil until soft. Strain through a cheese cloth or muslin. Squeeze the bag to not waste any juice, although this will result in a cloudy jelly.
Add the required amount of sugar and boil until temperature of 105 C is reached. Remove any foam from the boiling mixture. This takes about 30 minutes for 1kg of berries.