Am I asking too much of meringue to be able to keep a key lime pie in the refrigerator for 24 hours? The meringue ends up very wet at the end of that period. I keep it covered in the fridge.
The easiest way to prevent meringue from weeping is by adding a teaspoon of cornstarch to the recipe, which will absorb the excess moisture that causes it. If you're a bit adventurous, you can also opt to sprinkle some cookie crumbs over your filling so when it weeps, the crumbs will absorb the moisture.
Essentially a meringue in its most basic form is just egg whites whipped until the proteins coagulate and it traps air (to simplify the process). The meringue will weep in this form if it's over beaten and the liquid egg white splits out, it will also weep over time unless you stabilize it.
Sugar, stabilizes the whites however it can be further stabilized with 2 techniques.
If you make an Italian meringue, which is hot sugar syrup beaten into egg whites, it will last for longer. This is because the hot syrup partially cooks the egg whites and once cooled the sugar syrup hardens.
Using gelatin will make it last the longest. When making the Italian meringue, when you have combined the hot sugar, whip in a couple of teaspoons of powdered gelatin or 2 or 3 sheets of leaf gelatin (both softened in water). This will stabilize the egg whites and they could last a good 3 days. Just remember if you are going to caramalise the meringue, do it carefully as if it get too hot the gelling properties of the gelatin will be disabled.
Hope this helps!