Rice flour is the key ingredient that makes bhaji batter crispier. Adding a tablespoon or two to your regular batter mix will significantly improve the texture.
The crispiness of bhaji batter depends on several factors, but the type of flour used plays a crucial role. Rice flour, unlike wheat flour (besan), contains less gluten. Gluten development leads to a chewier texture, which is undesirable in crispy bhajis. When rice flour is added to the batter, it inhibits gluten formation, resulting in a lighter and crispier coating when fried. The starch in rice flour also contributes to the crispness as it dehydrates quickly in hot oil, creating a rigid structure. Other ingredients like hot oil and baking soda also contribute to the crispiness, but rice flour is the primary driver. To incorporate rice flour, simply mix it with your regular besan batter along with spices and water to achieve the desired consistency.
Don't overmix the bhaji batter! Overmixing develops gluten, even with rice flour present, leading to a tougher bhaji. Mix just until the ingredients are combined.