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HalfPint is a trusted home cook.
A large apple crumble (baked in a 13x9 pan) can serve about 8-10 people with generous portions. Most of recipes that I looked at use about 6-8 lbs of apples. So I would say about 20-25 lbs of apples for 30 people.
Nancy is a trusted home cook.
Brian - thinking about your apple crumble for 30, how are you fixed for baking pans?