Milk + Lemon Juice or Vinegar (Best Option)
1 cup milk + 1 tablespoon lemon juice or white vinegar (let sit 5 minutes)This substitute works because the acid (lemon juice or vinegar) curdles the milk slightly, lowering its pH to approximate buttermilk. The acidity reacts with baking soda in the muffin batter, producing carbon dioxide bubbles that help the muffins rise and develop a tender crumb.
For best results, use whole milk or 2% milk and allow the acid to sit in the milk for at least 5 minutes before mixing into the batter. This ensures proper curdling and acidity. Avoid using skim milk as it may reduce tenderness.
Compared to original buttermilk, this substitute yields very similar texture and flavor, with a slight difference in tanginess depending on the acid used. Overall, it preserves the lightness and moistness expected in muffins.