Place a small amount on the mixture on the place. The cold plate will help cool the mixture and give you a good indication if the jam is ready.
You may need to do this once or a couple of times depending on how soon you start checking.
You know when the jam is done; If the blob of mixture you placed on the plate wrinkles when you touch it with your fingers.
Just when you are ready to take the jam off the heat add a teaspoon of butter and you will notice that all the foam on the top will dissolve.
Let the Jam cool for about 20 mins before you pour it into a warm sterilized jar leaving 1/4 inch of the top.
Use a clean sterilized knife or spatula to move the jam a bit – this will remove any air pockets.
Clean the rim of the jar with a clean paper towel.
Top the lid and screw on rings (that come with the canning jars)
Place a piece of wax paper on the top before you place the lid on tightly.