Excellent jam and no Certo needed. The raspberries have natural pectin in their seeds and that is enough to thicken it. 5 lbs = 9 cups crushed berries.
- Use a very large pot.
- When the jam reaches a full rolling boil it will double in volume.
- Heat mashed berries until they reach a full rolling boil.
- Boil 2 minutes.
- Add sugar.
- Stir well.
- Bring to a boil, stirring constantly, boil for 2 minutes.
- Remove from heat.
- Beat with rotary beater for 4 minutes
- Pour in sterilized jars and seal.