I have a pie pastry question. PBS is airing a show about pies. They showed one

[dixiegrrrrl]

9. It's egg white

Obviously what you saw was using very beaten egg white.

Why does egg whites prevent a soggy pie crust?

Egg whites form a protective moisture between juicy pie fillings and your un-baked pie crust before and after baking.

Water blockers – egg white protein

Egg whites contain proteins. These proteins like to bind to each other. Protein structures have a molecular bond until heat or aggregation is applied.

As the egg whites heat up they start to coagulate or thicken, which helps push the wet pie filling away from the pie crust. Cooked egg whites swell to build a stronger structure that has a solid form. This solid form is rubbery like and will block water molecules from penetrating.

https://www.everythingpies.com/prevent-soggy-bottom-pie-crust/

Also one of my favorite sites for learning how-to about anything is: the spruce dot com..this is from their cooking page:

https://www.thespruceeats.com/how-can-i-prevent-a-soggy-bottom-pie-crust-480510#brush-the-bottom
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