In large stockpot, add berries. With a potato masher,mash down a few times in the pot to release the juice. Add sugar and water.
Turn heat on low and stir until sugar is dissolved.
Peel and slice apples. Put in a ziplock bag with lemon juice and salt. Shake, Shake, Shake.
Add rhubarb to the stock pot, mix well and then add the apple mixture. Stir.
Add instant tapioca. Do not use whole Tapioca.
Wash pint jars and place in 9x13 pan upside down and add hot water to pan. Heat oven to 250°.
Fill hot water bath canner with hot water.
Cover and start the water to boil.
Increase heat to medium for the stockpot, stir and cook about 15 minutes.
Add 1 cup cold water. Stir.
In bowl, add cold water and cornstarch, stir to dissolve and then stir in hot filling. Stir and cook until thickened and glossy. Pull off the heat.
Fill jars, leaving 1 1/2 inch head space.
Stick knife down the side of the jar to eliminate any air pockets. Wipe rim of jars.
With hot clean damp cloth. Put hot seal on each jar and screw on ring.
Place filled jars in canning rack, lower into boiling water. Cover. When water starts a rolling boil over the top of lids start to time, 20 minutes. Raise rack, place jars on toweled surface. Be careful.
Jars are hot and you don't want to click them against each other.
Note: You may add sugar to taste. This recipe is slightly tart because the family likes it this way.
Variations of the Pie Filling after Canning:
•Open one jar and add 1 cup sour cream. Serve cold or place in pie crust and bake.
•Open one jar and add 8 oz. cream cheese and mix well. Serve cold with cool whip or fill pie crust and bake.
•Use a cup or two from a canned jar and use as a swirl filling in bundt cake batter.