Milk + Lemon Juice or Vinegar (Best Option)
1 cup milk + 1 tablespoon lemon juice or white vinegar (let sit 5-10 minutes)Buttermilk’s acidity is crucial in brownies as it reacts with baking soda to produce carbon dioxide, which helps leaven the batter and create a tender crumb. Adding lemon juice or vinegar to milk creates a similar acidic environment that curdles the milk slightly, replicating buttermilk’s chemical properties.
For best results, use whole or 2% milk and allow the acid to sit in the milk for 5-10 minutes before adding to the batter. This ensures proper curdling and acidity. Avoid using skim milk as it lacks fat, which can affect richness.
This substitute maintains the expected rise, moistness, and slight tang of buttermilk brownies, resulting in a texture and flavor very close to the original recipe.