I canned apple pie filling but did not use thickener. (It was suggested that thickeners could cause problems) Now I'm not sure what to do with all the liquid (sweetened and spiced). Do I heat it with a thickener or just add thickener to cold liquid? How much should be poured over apples? Recipes seem to suggest using 2 quarts for 9" pie, jar probably holds 1 cup liquid per quart.