Milk is sensitive to high heat; it can lose nutrient value if exposed to temperatures that are too high, for too long. Heating milk in a microwave can lead to uneven hot spots which can cause unexpected scalding burns. The best way to heat cow's milk is to bring it to a slow simmer on the stove. You can heat breast milk to room temperature by placing it under warm water.
Heating Cow's Milk
Pour the milk into a small saucepan over medium heat.
Stir the milk gently with a spoon so it warms evenly. Reduce the heat to medium-low.
Add cocoa powder and chocolate, if desired. Stir the mixture.
Heat the milk until bubbles begin to form around the edges or until the chocolate and cocoa form a smooth consistency.
Heating Breast Milk
Pour warm water into a deep bowl and submerge a bottle of breast milk. To avoid contamination, keep the nipple away from the water as much as possible.
Empty the bowl when the water cools and refill it with warm water, if necessary.
Remove the bottle from the warm water. Move the bottle in a circular motion to mix the nutrients within the milk. Pour a drop from the bottle onto the back of your wrist to test the temperature. The milk should feel warm to the touch, not hot.