FSCN - Heat transfer

What is heat transfer?

The movement of molecules that transfers energy from one location to another. Heat moves from a warmer place to a cooler one.

Method of heat transfer: Convection

The transfer of heat through a fluid (liquid or gas) caused by molecular motion. Food is heated by a moving heat source. e.g. steaming, boiling, frying.

Method of heat transfer: Conduction

The transfer of heat or electric current from one substance to another by direct contact between the cooking surface and food. Slowest method of heat transfer. e.g. baking, pan frying and sautéing.

Method of heat transfer: Radiation

Energy that is radiated or transmitted in the form of rays or waves or particles. Heat waves strike and penetrate food. No direct contact. e.g. microwave, broiling.

Specific heat (Cp)

The amount of heat needed to raise the temperature of one gram of a material by 1 ºC.

Thermal conductivity

The ability of a food material to conduct heat through it.

Cp equation

Cp = 1.42 mc + 1.55 mp + 1.68 mf + 0.84 ma+ 4.19 mm
(m= mass fraction for carbohydrates, proteins, fats, ash
(minerals) and water (or moisture))

Cp = Q/mΔT (Q= heat gained or lost (kJ), m= mass of food (kg), ΔT= change in temp (C))

Role of water in cooking?

Heat transfer, Universal solvent, and Colloidal dispersions. Water transfers and moderates the effects of heat. Water ensures that the heat will be evenly and efficiently distributed.

Moist-heat (convection)

Heat transfer by moister (water, liquid, steam). e.g. boiling, braising, steaming, and steaming.

Dry-heat (conduction)

Involves the circulation of hot air or direct contact with fat to transfer heat. This method promotes caramelization and the Maillard reaction. e.g. pan frying, roasting, sautéing, stair-frying, deep frying, grilling, and baking.

What temperature does caramelization occur?

330°F / 165°C

What temperature does maillard browning occur?

250°F / 120°C

Maillard browning in most foods

Occurs under alkaline conditions with concentrated solutions of carbohydrates and amino acids. Prolonged cooking times promote the gradual development of Maillard colors and flavors. e.g. beer and simmered egg whites.

Why does food cooked in hot water or steam usually have bland and mild flavors?

Because water cannot rise above 212°F / 100°C whereas maillard browning and caramelization occurs at higher temperatures.

Freezing

Preserves food by slowing chemical reactions and inhibiting microbial growth due to lower water activity. It can affect the texture and tissue of fruits and vegetables, and by limiting air exposure, it also helps prevent oxidation.