Living on a beautiful tropical island, surrounded by warm, blue-green, ocean waters and constant cooling trade winds pretty much guarantees that our baking ingredients, will be affected by the humidity or moisture in the air. To test the effects that humidity has on some ingredients, I made my favorite pound cake at home on St. Croix, and then made the exact same recipe when I went to visit my sister in Florida in her air-conditioned home. The difference was a much improved textured cake in Florida! The Reason? Less humidity. This is especially the case with flour and baking powder that can absorb a lot of the air’s moisture. I try to overcome this by storing my flours in airtight containers. I also always use a kitchen scale to measure my flour. It is a much more accurate way to measure, especially for a first time recipe. In the case of baking powder, I add a tiny bit extra than the recipe calls for. And if all else fails, and I need fool-proof results, I buy a fresh bag of flour from the store.
Also, if you don’t have a scale, you can try the “Dip and Sweep” method. Using the measuring cup, aerate the flour by lifting and stirring it in the bag. Then dip the measuring scoop in and sweep off the excess with the back of a knife.