Sandy asks: Would there be a bitter taste to a pie crust that had been made with whole wheat flour that was several years old? The flour had been kept in glass containers with tight lids but not in a dark cool place. I made an apple pie, and when I had a bite, there was a bitterness to the piece. I can’t think of any other of the ingredients that would have affected the taste.
Baking S.O.S. says: Yes, I am sure you are right. Whole wheat flour tends to go bad more quickly than white all-purpose flour. This is because there is some natural oil in the whole wheat kernel that gets ground into flour when the entire wheat kernel is milled (vs. white flour, where the bran and germ are removed). This natural oil will go rancid fairly quickly if the flour is not stored properly. So the rancid oil is probably what you are tasting when you say the pie crust tastes bitter.
Whole wheat flour only tends to keep for about 3 months, even when stored in an air-tight container in a dark place. For longer storage, I recommend putting the whole wheat flour bag in a freezer zipper bag and storing it in the freezer. It should keep for many months–up to a year–in the freezer. It is a good idea to write the date on the bag, as well, so you know how long it has been stored in the freezer and when it might be time to throw it out if you haven’t used it in a while.
This is a frustrating experience, I know, as I have learned it myself the hard way! Now I always store my whole wheat flour in the freezer to avoid this problem.