This past Friday I ended up baking a small cherry cake for our family. The recipe was very simple - it only had 5 ingriedents: flour, baking powder, eggs, oil and pie filling. Unfortunatly, after the cake was baked, it turned out that it tasted very bitter to me. My wife on the other hand, did not taste anything unusual. To add more to this mystery, I have been tasting a bit of bitterness in some baked goods at my home for quite some time. My first thought was an egg substitute but after some research, it was something entirely different.
It turns out that the blame is on the baking powder. There are two reasons why baking powder can cause something to taste bitter:
1. Some people are sensitive to a specific type of baking powder. It turns out that there are TWO types of baking powder - one containing a salt called "sodium aluminum sulfate", and others that don't. This particular salt is bitter according to this page and this page. Wikipedia seems to imply that some people are more sensitive to its taste than others. While there has been healthy concerns, it does not look like they were confirmed.
2. Using too much baking powder causes bitterness. According to this page at Joys Of Baking, too much baking powder can cause bitter taste. The normal proportion is about 1 to 2 teaspoons per 1 cup of flour. This recipe had a mistake - 2 TABLESPOONS instead of 2 tea spoon.
While I was researching this, it turns out that for the past year we used to use non-aluminum baking powder made by Rumford. However, recently we ran out, and when I went to check the cupboard, it turns out that we switched to a different brand made by Clabber Girl which contans aluminum.
If you feel particularly lazy to go shopping, Amazon sells Rumford baking powder online with free shipping right here.
P.S. The only reason why I am bothering to post this is because it took me more than 20 minutes of Googling to find the right answer. I am hoping that my post will help others find the answer quicker.