A “haybox” is a cooker that utilizes the heat of the food being cooked to complete the cooking process. Generally, it takes three times the normal cooking time to cook food in a haybox.
This highly insulated unit is made for military use to keep food or fluids hot or cold. It’s a very effective system and can keep ice frozen for days.
Description: This example is known as a Mermite Tactical Military Cooler that first began production in the 1960s and was manufactured and used through the 1990s. It consists of an insulated outer shell and three internal containers, with a capacity of 1.5 gallons of food per container. Therefore, all three containers can hold 4.5 gallons.
History: Hayboxes are so called because originally hay or straw were the commonly used insulators. Pots of food would be brought to a boil and then placed in a box filled with hay or straw. During the Second World War, hayboxes were used to conserve rationed cooking fuel.
Advantages and Disadvantages: Haybox cooking can save vast amounts of fuel, but there is a risk of bacterial growth if the food items are allowed to remain in the danger zone (41−140 °F or 5−60 °C for one or more hours. To reduce the risk, food cooked in hayboxes can be reheated to boiling before eating, or a food thermometer may be used.