Taiyaki not forming correctly

I've been practicing making Taiyaki and my recipe seems to work. But I recently changed it a bit to make the batter chocolate flavored.

Here's the recipe I used:

  60g All purpose flour
  55g Sweet rice flour
  10g Cocoa powder
  40g Sugar
   8g Baking powder
   3g Salt
    1 Egg
200ml Milk
  3ml Vanilla

I fill one side of the taiyaki mold with a thin layer of batter, add the filling, then cover it up with more batter. I close the mold, flip it and let it cook for a few minutes. When I open it, one of two things happen:

The mold isn't completely filled even though I put batter all the way to the top. I end up with 3/4 of the fish.

Both sides are filled but when I open the mold, the taiyaki is split in half - like it didn't seal or each side cooked on its own and now I end up with two halves of the fish.

Note that the technique I do works well with the plain batter (not chocolate flavored). Is there something wrong with the recipe or am I doing something else wrong?

Best Answer

Since you say that you replaced some of the wheat flour with cocoa powder, that might explain it.

My theory:

In comparison to wheat flour, cocoa powder contains no gluten. Gluten is the glue that helps hold baked products together, making them less crumbly/fragile. Also, cocoa powder contains less starch than wheat flour.

In addition to the reduction in gluten and starch, cocoa powder also generally contains much more fat than flour. Unfortunately fat acts as a shortening agent, making the finished product more cake-like and crumbly, and fat can also inhibit gluten development.

I fear you've basically changed the composition of the batter too much, making the finished product too fragile to remove from the mould in one piece.

A possible fix:

Use a wheat flour with a higher gluten content such as bread flour, in order to help compensate for the addition of cocoa powder. Maybe also let the mixture stand a little while longer before pouring it into your moulds. A little extra time can also help develop the gluten.

I have the feeling that this may require some trial and error. I make no promises that it will actually work. Maybe test using a small batch so you don't waste too much of your ingredients while experimenting.