A haybox, also known as a fireless cooker, is a type of oven or device that traps the heat from a hot pan and the food it contains, allowing the food to finish cooking without requiring an additional heat source. The simplest form of a haybox is a box with a lid that is lined with some type of loose insulation. The pot of food being cooked is taken to a boil and then placed in the box, after which it is sealed with a lid and left to cook. In general, a haybox requires several hours to finish cooking food, although a properly sealed cooker also can keep food very warm for a long time, sometimes overnight. The box can be used in a kitchen to reduce the amount of gas or electricity consumed, or it can be used in a portable form while camping, when long cooking times over a fire are not possible.
The construction of a haybox is designed to keep heat inside the box and near the food. This means the box must be made with sealed edges and corners, and a lid that attaches firmly to the top. Inside the box, the walls must be insulated in a way similar to some homes. The insulation used against the walls must be made from a material that is heat-resistant, non-toxic and packed loose enough to be able to hold the hot pockets of air inside while keeping cold air out.
The material originally used for insulation was hay, giving the box its name. Other types of insulation that can be used include shredded paper, certain types of foam, dry leaves, thick cloth or rice. Some hayboxes enclose the insulation in a layer of foil so the heat reflects back inside the box, while others enclose it to prevent the material from releasing harmful chemicals.
To use a haybox, food first must be prepared over a conventional stovetop or other heat source. Before placing the food in the fireless cooker, it needs to be boiled for a time so the food and the pot absorb a sufficient amount of heat. The box will work best with foods that are in a heavy pot and in some type of liquid, such as broth or water. Both the weight of the pot and the density of the liquid will help to hold more heat for a longer time.
It can take several hours for a meal to finish cooking in a haybox, even if the food would cook in only a few minutes over direct heat. The benefits of a haybox are that food will not burn and liquids will not evaporate as aggressively as they would over a normal fire. It should be noted, however, that the temperature inside a haybox drops slowly over time, so there is a chance that harmful bacteria could take root in the food if it is not eaten in a timely manner.