Combine the cranberries and raspberries in a large pot.

Add the sugar and water. Bring it to a boil, reduce to a simmer and cook for approximately 30 minutes - 45 minutes, until the fruit is nice and mushy. The cranberries will "burst".

Strain the liquid through a fine mesh sieve lined with a paper towel or a cheesecloth. Discard the cooked berries. Cool.

I usually store the concentrate in 2 liter canning jars. You will have approximately 5 ½ liters of concentrate.

When you're ready to serve, dilute the concentrate with water or seltzer water. You can also add some mint.