The water in a steamer should be boiling to create the steam necessary for cooking food effectively. A vigorous boil ensures consistent and sufficient steam production.
Steaming relies on the heat from water vapor to cook food. When water boils, it transforms into steam. This steam circulates around the food in the steamer basket, transferring heat and cooking it. A simmering temperature, while still producing some steam, may not generate enough consistent heat to cook the food evenly or efficiently. A full, rolling boil provides a constant and ample supply of steam, ensuring the food cooks thoroughly and retains its moisture. The intensity of the boil can be adjusted slightly depending on the food being steamed; delicate items might benefit from a slightly less vigorous boil to prevent overcooking. However, the water should always be actively boiling, not just simmering.
Always check the water level in your steamer periodically, especially during longer steaming sessions. Running out of water will stop steam production and can damage your steamer.