Heat Transfer:
* Conduction: The heat from the hot stones transfers to the food directly through contact. This is most prominent when the stones are buried directly with the food.
* Convection: As the stones heat the air within the earth oven, the hot air circulates, further cooking the food. This is especially relevant for food placed on the top layer of the hangi.
* Radiation: The hot stones radiate heat, contributing to the overall cooking process. This is less significant compared to conduction and convection, but still plays a role.
Thermodynamics:
* Specific Heat: Different types of stones have different specific heat capacities, meaning they absorb and retain heat differently. Māori traditionally use river stones, which absorb heat well, ensuring a consistent cooking temperature.
* Heat of Fusion: The process of melting ice to create steam for cooking involves the heat of fusion, which is the energy required to change the state of matter from solid to liquid. This plays a role when using ice in the hangi.
Other Physics:
* Pressure: The weight of the earth above the hangi creates pressure, which can help to cook certain foods, such as root vegetables, more evenly.
* Buoyancy: The hot air within the hangi creates a buoyant force that helps to lift the food, preventing it from being crushed by the weight of the earth.
* Insulation: The earth acts as an insulator, trapping the heat from the stones and maintaining a consistent cooking temperature.
Optimization:
* Stone Selection: The size and type of stones are crucial for optimal heat transfer and distribution. Larger stones retain heat longer, while smaller stones heat up faster.
* Food Placement: The placement of food within the hangi is important, as different foods require different temperatures and cooking times.
* Earth Type: The type of soil used for the hangi can affect its ability to retain heat and insulate the food.
By understanding these physics principles, Māori have developed a highly efficient and sustainable cooking method that has been passed down through generations.
