A viewer recently e-mailed me to say that when she added fresh blueberries to her favorite muffin batter the finished muffins had an unappetizing greenish haze around the blueberries. She wondered what caused it and if there is a way to prevent that from happening.
When you bake with fresh or frozen blueberries, the color is affected by the level of acidity in the batter. If the batter has a bit too much baking soda, the blueberries turn green around the edges. You can balance the acidity by using a recipe that calls for buttermilk or another acid, such as orange juice or lemon juice.
Another problem that I get an occasional question about is, How can I keep the blueberries from all ending up on the bottom of my muffins?” One solution is to use a thicker batter. Or, don’t mix the blueberries into the batter at all. Fill the muffin cups two-thirds full with batter, then dot the tops with several blueberries. They will distribute themselves as the muffins bake.