Do not make meringues that have less than 2 tablespoons of sugar per egg white. If you use any less, the foam will not set and the meringue will shrink. Also, meringues may shrink during baking, separating from the crust. This is caused by the meringue not clinging to the crust. Make sure the meringue is spread over the hot filling and touches the crust around the entire edge; do not leave any openings around the pie.