Glass baby bottles have become increasingly popular due to concerns about toxic chemicals in plastic bottles. Warming milk, breast milk or formula in glass baby bottles is a relatively easy process and can be done safely in a number of different ways.
Under Hot Running Water
One of the safest ways to heat the contents of a glass bottle is simply to put the filled bottle under hot running water until the milk reaches the desired temperature. Although it is time-consuming, this method makes it almost impossible to overheat the bottle contents and no extra equipment is necessary.
On the Stovetop
Another effective method is to place the filled bottle in a pan of water and heat it on the stovetop, or in a pan of water that has just been heated, for a few minutes. The water should be very warm, not boiling. Test the milk to make sure it is not too hot for your baby. Never place a frozen bottle of milk directly into very hot water, as the temperature change could crack the glass.
In the Microwave
Microwaving milk in glass baby bottles is generally not recommended as it tends to heat milk unevenly and may make the glass very hot. If you choose to use this method, be sure to remove the cap and nipple before heating and carefully check the temperature of both the milk and the bottle before giving it to your baby.
In a Separate Container
For caregivers who are uncomfortable warming milk in a glass bottle, another option is to heat the milk outside of the bottle and then pour it in. This can be done using very low heat on the stovetop or in the microwave.
It is strongly recommended that you use the stovetop or running water methods to heat breast milk. Use warm, not very hot, water. Never warm breast milk in a microwave; it can destroy the milk's nutrients.