Q: In a recipe I read recently it said to use a ‘bain-marie’. What is this and how does it work?

A bain-marie is a water bath made by placing a container in which you are cooking something into another vessel with water in the space between. It is used for delicate dishes such as egg custards or sauces that may be damaged by too much heat.

A bain-marie is normally made by placing the food dish into a roasting pan, pouring boiling water into the roasting pan until it comes about half way up the side of the inner dish, and putting the whole lot into an oven set to about 325°F-350°F (165°C-175°C). A wire rack may be placed under the food dish to help distribute heat on the bottom. “Bain-marie”, on occasion, also refers to a double boiler used on the stovetop – one pot that is nested on top of another. The pot on the bottom is filled about a quarter full of water, lower than the bottom of the upper vessel, and heated on the stove. The food being cooked, or melted, is placed in the top pot.

The temperature at which the food is cooked is regulated by a bain-marie to be no higher than the boiling point of water. To understand why, try this experiment. Place a pan of water on the stove and heat it, measuring the temperature at regular intervals using a cooking thermometer. You will notice that the temperature rises until the water starts to boil and then stays constant until nearly all of the water has boiled away. At sea level, this temperature will be 212°F (100°C). Because the water or steam is what carries heat to the dish holding the food, the cooking temperature cannot be higher than this.

At higher altitudes, water will boil at a lower temperature. This means that food cooked in a bain-marie may take longer to finish. The rule is that water will boil at 1°F lower temperature for each 500 feet you are above sea level. The effect on cooking time will depend on the recipe, so you may need to use other methods than time to check foods such as egg custards. A paring knife inserted into the middle of a properly cooked egg custard should come out clean and dry.