Rice flour is the key ingredient that makes pakora batter crispier. Adding a tablespoon or two to your regular batter will significantly improve the texture.
The crispiness of pakoras depends on the batter's ability to release moisture quickly during frying. Rice flour, unlike wheat flour (besan), contains less gluten. Gluten development in the batter leads to a chewier texture. By incorporating rice flour, you reduce the overall gluten content, resulting in a lighter and crispier coating. The rice flour also absorbs less oil, contributing to a less greasy final product. You can experiment with different ratios of besan to rice flour to achieve your desired level of crispness. Start with a ratio of 3:1 (besan to rice flour) and adjust from there. Other ingredients that can contribute to crispiness include cornstarch or semolina, but rice flour is generally considered the most effective.
Don't overmix the pakora batter! Overmixing develops gluten, leading to tougher pakoras. Mix just until the ingredients are combined, leaving some small lumps. This will help keep the pakoras light and crispy.