White Vinegar (Best Option)
1 teaspoon per 1 tablespoon lemon juiceWhite vinegar is an excellent acidic substitute because it reacts with baking soda to produce carbon dioxide, which helps brownies rise and develop a tender crumb. Its neutral flavor ensures the chocolate remains the star.
When using white vinegar, measure precisely to avoid an overly tangy taste. Mix it well into the batter to ensure even leavening. Avoid using too much as it can impart a slight vinegar aftertaste.
Compared to lemon juice, white vinegar maintains the acidity needed for leavening but lacks the citrus aroma, resulting in brownies that are slightly less bright in flavor but equally tender and moist.