Overmixing crepe batter develops too much gluten, resulting in tough, rubbery crepes instead of delicate, tender ones. A few lumps are okay!
Crepe batter, unlike bread dough, benefits from minimal gluten development. Gluten is a protein found in wheat flour that, when mixed with water, forms elastic strands. These strands provide structure and chewiness, desirable in bread but not in crepes. Overmixing vigorously activates gluten formation. This leads to a crepe that is chewy, dense, and lacks the desired light and airy texture. The goal is to gently combine the wet and dry ingredients until just incorporated. A few small lumps are perfectly acceptable and will disappear during the resting period. Resting the batter allows the gluten to relax, further contributing to a tender crepe.
Use a whisk for initial mixing, but switch to a spatula to gently fold in any remaining flour. This helps prevent overmixing and ensures a light and delicate crepe.