Liz asks: I have been using the same zucchini bread recipe for a number of years. Over the past few months, every time I make it, it comes out flat and very dense. I have tested my baking soda and baking powder and they are both fine. What else could be causing this problem?
Baking S.O.S. says: I, too, have experienced the exact same problem with my favorite cake recipe. Sometimes it turns out just fine, but other times, it is very dense and even RUBBERY. (yuck!) Over the years, I have tried a number of different variables to solve the problem because I love the cake recipe too much to give up on it.
I finally came to the conclusion that the original recipe simply did not contain ENOUGH leavening agents (baking powder & baking soda), so I added more baking powder to my original recipe. Since you have tested your baking powder and baking soda to confirm that they are still fresh and active, then I would suggest the next step is to look at the quantity of baking powder and baking soda called for in the recipe.
Baked goods can fall in the center or become heavy and dense in situations where you have either too much OR too little leavening, so it can be tricky to determine which it is!
As a general rule, there should be 1 tsp. of baking powder OR 1/4 tsp. of baking soda for every 1 C. of flour in the recipe. Take a look at your original recipe and see how much baking soda or baking powder it calls for per each cup of flour. If there is too much leavening, cut back on the baking powder using the ratio above. (You will still need baking soda to counter-act any acidic ingredients in your recipe, including the zucchini.) If you do not have enough leavening, add some baking powder according to the formula above. My guess is that you could probably add a little baking powder to your recipe to help it rise more. (But beware: too much baking powder can cause your product to taste bitter.)
One other option to consider is your oven temperature. Since you mentioned that it has only been the past few months that you have started experiencing problems with your recipe, I wonder if it could be a problem with the oven rather than the recipe?
Have you used an oven thermometer to gauge the internal temperature of your oven as it preheats? I recently had oven problems, and my repair person told me that with some gas ovens, they will eventually start to lose pressure and slowly lose their heating power over time. It may not be noticeable at first.
If your oven is not actually getting up to the necessary temperature, then your zucchini bread will not rise quickly enough, and it will end up heavy and dense. Baking powder needs a hot oven to activate it quickly and force it to make your product rise. Try checking your oven temperature, too. That could also make a difference.
I hope one of these suggestions will help. Good luck!