Either Andy did his homework or is just naturally smart?
I guess I posted this because sometimes you can follow a recipe to the letter and it just doesn't turn out right. You think it's your fault - when the truth is that it's the fault of the recipe!
The problem in both cases is a lack of gluten. Gluten forms a tight elastic network that is able to hold gas in - think of bubble-gum here. Without gluten the CO2 produced by the yeast just floats off into space. It's kind of like trying to blow up a pair of pantyhose like a party balloon - no matter how much air you blow into them their not going to puff up.
But - the lack of gluten production is for two different reasons.
1. Rye flour doesn't contain enough glutenin and gliadin for significant gluten production. Andy's approach is one solution. The other, to retain more of the rye flavor, would be to add 1/3 cup "Gluten Flour" and a little more liquid to the original recipe to get a risen loaf.
2. The King Cake's problem is
because of the sugar. Glutenin and gliadin bond with sugar easier and faster than they bond to each other. And, when they are already bound to sugar they don't bond with each other to make gluten. The simple solution here was to reduce the sugar to 3 Tablespoons (1 Tblsp per cup of flour).
Source material (problems and solutions) taken from: CookWise
by Shirley M. Corriher - page 98.