Overmixing pancake batter develops the gluten in the flour, resulting in tough, flat pancakes instead of light and fluffy ones. Mix just until the ingredients are combined.
Pancake batter relies on a delicate balance to achieve its signature fluffy texture. Flour contains gluten, a protein that, when hydrated and agitated, forms elastic strands. While gluten is desirable in bread, it's the enemy of tender pancakes.
When you overmix pancake batter, you excessively develop the gluten. This creates a network of strong gluten strands that make the pancakes chewy and dense. The batter also becomes thicker, preventing the pancakes from rising properly. The carbon dioxide produced by the baking powder or baking soda gets trapped in the gluten network, leading to flat, rubbery pancakes.
Ideally, you should mix the wet and dry ingredients together until *just* combined. A few lumps are perfectly fine – in fact, they're preferable! These lumps will disappear during cooking, and the minimal mixing will prevent gluten development.
Use a whisk for gentle mixing and stop as soon as the dry ingredients are moistened. Don't worry about achieving a perfectly smooth batter; a few small lumps are okay and will result in a lighter, fluffier pancake.