A dessert recipe that proves that you don't need fat to make the food tasty -- lots of sugar works too! But really, this is a very enjoyable treat. It is very flexible; I like it best with rhubarb, but anything with about the same acidity of the listed fruit should be good. For something even better, try topping a little crumble with a dollop of ice cream. Mmmm.
Mix all the filling ingredients in a bowl and stir to coat the fruit with the sugar and flour. Set aside for 20 minutes.
Mix the dry ingredients for the topping. Dribble enough of the apple juice concentrate over the mix to moisten it; mix it up.
Put the fruit into a 9 x 12 inch pan, and spread the topping over the top. Bake at 375 degrees (Farenheit) for 20 minutes.