Fritter batter is best used immediately, but can sit for up to 30 minutes at room temperature or up to 2 hours in the refrigerator. After that, the leavening agents may lose their effectiveness.
The ideal time to fry fritters after mixing the batter depends on the ingredients and the leavening agent used. Most fritter batters contain baking powder or baking soda, which react when mixed with wet ingredients to create air bubbles, resulting in a light and airy fritter. This reaction begins immediately upon mixing.
If the batter sits for too long at room temperature, the leavening agents will exhaust themselves, and the air bubbles will dissipate. This will result in dense, flat fritters. Generally, you should aim to fry the batter within 30 minutes of mixing.
If you need to prepare the batter in advance, you can refrigerate it for up to 2 hours. The cold temperature will slow down the leavening process. However, it's important to note that the batter may still lose some of its rising power, so the fritters might not be as light and fluffy as if fried immediately. Before frying refrigerated batter, gently stir it to redistribute any settled ingredients. Avoid over-stirring, as this can deflate the batter.
To test if your batter is still good, drop a small spoonful into hot oil. If it puffs up nicely, the batter is still active. If it stays flat and dense, it's best to make a fresh batch.