Why doesn't my rice-flour cake rise with fruit?

Question

MY rice flour cakes always rise nicely, resulting in a fluffy cake. When I add pieces of fruit (mostly fresh) like cherries in a chocolate cake, apples in an apple cake or shredded sweet potato, the cake rises just a little bit. There are some microscopic air bubbles, but it is basically one thick clump of (nevertheless soft) dough. It isn't fluffy or has air bubbles at all. Why is this, how can I improve it?

This is the basic recipe I use: rice flour, eggs, and baking powder (bicarb + acid). Then there are some varying things regarding taste, like salt, sugar, chocolate etc. Note that there isn't any milk.

Answer 1

You don't list your process and ratios, but this looks like something in the middle between a cake and a souffle, or maybe something close to a gluten-free genoise.

The structure you get in this kind of sponge is incredibly delicate. It's mostly all egg-based, both for the leavening action and for the structural integrity. Consequently, throwing in a bunch of wet fruit is no better than throwing wet fruit into whipped egg whites - the liquid disrupts the foam. It's also sensitive to simple weight - I have made a gluten-free genoise with different flours, and when a flour is ground to a larger particle size, it basically falls down to the bottom during baking, creating a thick inedible layer. I don't think that the exact same mechanism is happening with dried fruit, but this is probably part of it.

In the end, gluten-free recipes are simply not robust to changes. If you want a gluten-free recipe with fruit, search for an existing recipe with fruit, instead of changing the one you have.

Answer 2

I can think of three things that might be going on here.

First, if your baking powder is "double-acting" (i.e. with a heat-activated acid) the acid from the fruit may be neutralizing the sodium bicarbonate in the baking powder. That means that during baking when the baking powder's acid is activated there's not enough bicarbonate to react with. If this is the case, adding some baking soda with the baking powder should help. If the fruit is just pieces of fruit and doesn't significantly suffuse the batter with juice, though, it's probably not the case.

Secondly, it could just be the fruit weighing down the batter, ripping open the foam as it forms. Gluten-free crumb is quite delicate during baking. I would only suspect this if, after baking, the surface of the cake was cratered by the fruit (or if there were a LOT of fruit and the surface was uneven).

Thirdly, the fruit could be a red herring and other "things regarding taste" you'd also changed were the real cause. Salt, sugar, and chocolate all affect the texture and behavior of batter.

Answer 3

Many fruits contain enzymes (amylases) which break down starch. Dough needs the structural support of starch to rise and keep the shape, so having the long starch molecules chopped down by enzymes severely undermines the structural stability of dough.