Jam must contain 66% sugar, (natural fruit sugar + added sugar) to obtain the right texture.
If one doesn’t want to add so much sugar, then the jam is no longer a true jam (according to the MAPAQ) but rather a spread. If one reduces the amount of sugar one must add pectin (made from apple peel) because it is the amount of sugar which gives the thicker, jam-like texture with the pectin in the fruit.
One can also add fruit which contains a high level of natural pectin such as apples, cranberries, plums, lemons, oranges or redcurrants.

Sugar is also a preservative and a minimum of 30% sugar in total (fruit sugar and added sugar) is required to conserve the jam for a few months. Spreads will not last as long as jam. Keep spreads in the fridge once they have been opened.

Proportions

	%	grams
Mixed berries	56,00	4000,00
sugar	23,60	1685,71
apple sauce	20,00	1428,57
no sugar needed pectin	0,20	1-2 packages
lemon juice	0,20	14,29
total	100,00	7142,86

Receipe

If you change the quantity of fruit, the quantities of the other ingredients must be modified as per the percentages in the chart.

Mix all the fruit (including the lemon juice) with the apple puree and heat the mixture until the fruit has softened and liquefied. You can speed up the process by using an immersion blender and this avoids cooking the fruit for too long, (which changes the taste). Then add 80% of the sugar and taste the mixture. Add the rest of the sugar as needed. Bring the mixture to the boil. Add the pectin, (using  » No sugar needed pectin  » from Bernardin) and mix together for another 2 or 3 minutes.
If you have used 10 to 20% of cranberries in your berry mixture you will probably not need the pectin, unless you want a really thick spread.
The temperature should be at least 80 degrees to ensure that the jars are sterilized when the mixture is put in. The jars must immediately be sealed and then turned upside down for one minute to ensure that the tops are sterilized too.
Cool the jars rapidly in iced water or outside to stop the cooking process and to conserve the colour and taste.

Bon appétit !