Over-mixing the batter

The way you mix your banana bread batter is critical, as it is with most baked goods. Novice bakers frequently fear under-mixing in order to avoid clumps of flour that will ruin the final product, but perfectly smooth batters do not guarantee a pristine baked treat.

Too much mixing time can result in a dense and gummy loaf. According to Baking Kneads, that undesirable texture develops as a result of too much gluten. Strong gluten formation is desirable in yeasted bread such as brioche, but it is undesirable in quick bread such as banana bread. To achieve a soft, tender crumb, mix the dry ingredients into the batter until just combined, then stop. Don't be concerned if your batter has visible lumps. The batter will even out while baking as long as there aren't large amounts of unincorporated flour.