As a sommelier and brewer, I can confidently say that a double boiler is not designed to boil water. Instead, it is specifically designed to heat items using steam rather than direct contact with hot water.
When using a double boiler, the bottom pot is filled with water, typically about two inches or 5.08 centimeters deep. This water is heated, creating steam that rises and gently heats the contents of the upper pot or bowl. The upper pot or bowl should not be in direct contact with the water in the bottom pot.
The purpose of a double boiler is to provide a gentle, indirect heat source for delicate items that require slow and even heating. This method helps to prevent scorching or burning, which can easily occur when using direct heat. It is commonly used for melting chocolate, making custards, sauces, or delicate ingredients that require gentle cooking.
Using a double boiler allows for precise control of temperature, as the steam provides a consistent and regulated heat source. This is particularly important when working with heat-sensitive ingredients, as overheating can ruin the texture or flavor of the final product.
In my personal experience as a brewer, I have used a double boiler when making certain types of beer that require precise temperature control during the mashing process. The gentle heat provided by the double boiler helps to extract the desired flavors from the grains without overheating or scorching them.
To summarize, a double boiler is not meant to boil water. Instead, it is a specialized cooking tool used for gentle and indirect heating, primarily through the use of steam. It is particularly useful when working with delicate ingredients that require slow and even heating to achieve the desired results.