It is generally okay to let brownie batter sit for a short period before baking, but there are some factors to consider to ensure the best results:
Leavening agents: If your brownie recipe contains baking powder or baking soda as leavening agents, it's best to bake the batter as soon as possible. Once these leavening agents come into contact with the wet ingredients, they start to react and release gases, which create air pockets in the batter. If you let the batter sit for too long, these gases may escape, and your brownies might not rise as well during baking.
Batter consistency: Some brownie recipes may include ingredients like eggs, which can cause the batter to thicken as it sits. If your batter becomes too thick or sets too much, it may result in denser and less tender brownies. To avoid this, it's essential to follow the recipe instructions and not let the batter sit for too long.
Cocoa powder: If your brownie recipe contains cocoa powder, letting the batter sit for a short while can allow the cocoa to hydrate fully, resulting in a smoother and more cohesive batter.
Flavor development: Allowing the batter to rest for a little while (usually around 10-15 minutes) can give the flavors a chance to meld, potentially enhancing the overall taste of the brownies.
In summary, it is generally okay to let the brownie batter sit for a short period before baking, but it's best to proceed with baking relatively soon after mixing the ingredients. If your recipe contains leavening agents like baking powder or baking soda, it's especially crucial not to delay baking, as this could affect the brownies' rise. Always refer to the specific instructions in your recipe for the best results.