1pkg (1.75 oz)Sure Jell Fruit Pectin for Less or No Sugar Recipes*
zest from 1 lime
To crush blackberries, work in batches by placing a layer of berries in a bowl and mashing with a potato masher until pulpy. Continue mashing layers until you have 3½ dry measuring cups worth of mashed berries.
In a large sauce pan, stir the sugar and pectin together until mixed. Stir in 1 cup of water. Bring the mixture to a boil on medium-high heat, stirring constantly. Continue to stir and boil for 1 minute. Remove from heat.
Add the crushed blackberries and lime zest into the large sauce pan with the pectin mixture. Stir for 1 minute.
Fill jars immediately with prepared jam. Leave 1/2 space at the top of each for expansion during freezing. Cover with lids.
Let stand at room temperature for 24 hours. After that, refrigerate up to 3 weeks, or freeze up to 1 year.
*if you are using another brand of fruit pectin other than Sure Jell, (such as Ball, Certo or MCP), follow the instructions provided with the pectin instead of the instructions I have provided, otherwise the jam may not set correctly.