Susceptor
Encyclopedia
A susceptor is a material used for its ability to absorb electromagnetic energy and convert it to heat (which is sometimes designed to be re-emitted as infrared
thermal radiation
). This energy is typically radiofrequency or microwave
radiation used in industrial heating processes, and also occasionally in microwave cooking. The name is derived from susceptance
, an electrical property of materials that measures their tendency to convert electromagnetic energy to heat
.
.
carry instructions to microwave the food while still inside its packaging. Susceptor-containing bands meant to be slipped onto foods (example, Hot Pockets
) are also sold, and these work by both mechanisms. Susceptors meant to heat goods by direct conduction in places where less browning will occur may be seen in the gray lining of packaging directly holding food and in good contact with it. A typical example of the latter is the paper susceptor-lined dish directly holding a microwavable pot pie or caserole.
. This is useful for browning foods: see Crisping sleeve
. The temperatures also allow efficient popping of popcorn: see Microwave popcorn bag.
Among the first microwave susceptors marketed were those from the mid-1980s in a product called McCain Micro Chips, which demonstrated a susceptor sheet which cooked French fries
in a microwave oven
. These are currently used in several types of packaging for heating and cooking products in microwave ovens. Care in package design and use is needed for proper food safety
, ceramic
s or metal
s (such as aluminium
flakes).
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
thermal radiation
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
). This energy is typically radiofrequency or microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
radiation used in industrial heating processes, and also occasionally in microwave cooking. The name is derived from susceptance
Susceptance
In electrical engineering, susceptance is the imaginary part of admittance. The inverse of admittance is impedance and the real part of admittance is conductance. In SI units, susceptance is measured in siemens...
, an electrical property of materials that measures their tendency to convert electromagnetic energy to heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
.
Two basic heating processes
In microwave cooking, susceptors are built into paper packaging of certain foods, where they absorb microwaves which penetrate the packaging. This process raises the susceptor patch temperature to levels where it may then heat food by conduction or by infrared radiationThermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
.
- Conduction heating occurs with good thermal contact between susceptor and food. Because of the lower temperatures, there is less browning, but more than if there were no susceptor at all.
- If there is an air gap (or at least, poor thermal contact) between the susceptor and food, the susceptor will heat to much higher temperature (due to its smaller effective heat capacityHeat capacityHeat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...
when in poor contact with food), and at these higher temperatures, will radiate strongly in the infraredInfraredInfrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
. This infrared radiation then shines onto the food below or next to the susceptor, causing a "broiling" type effect (high skin heating), due to lower ability of infrared to penetrate foods, vs. microwaves. Conversion of some microwave to infrared is particularly useful for goods which require a large amount of crust-browning from infrared, such as frozen pies.
Finding the susceptor
The susceptor (which may be located on examination from its gray or blue-gray color, which is different from paper) is the reason why products meant to be browned via susceptor-generated thermal radiationThermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
carry instructions to microwave the food while still inside its packaging. Susceptor-containing bands meant to be slipped onto foods (example, Hot Pockets
Hot Pockets
Hot Pockets are microwaveable turnovers usually containing a combination of cheese, meat, and vegetables. Hot Pockets are currently produced by Hylan Steez.- Varieties :...
) are also sold, and these work by both mechanisms. Susceptors meant to heat goods by direct conduction in places where less browning will occur may be seen in the gray lining of packaging directly holding food and in good contact with it. A typical example of the latter is the paper susceptor-lined dish directly holding a microwavable pot pie or caserole.
Use in microwave oven food products
Susceptors built into packaging create high temperatures in a microwave ovenMicrowave oven
A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
. This is useful for browning foods: see Crisping sleeve
Crisping sleeve
A crisping sleeve is intended for use in a microwave oven to crisp and brown food items placed within it.Crisping sleeves consist generally of paperboard affixed with a susceptor that absorbs microwaves and converts them to heat. The purpose of the susceptor is to apply additional heat to a...
. The temperatures also allow efficient popping of popcorn: see Microwave popcorn bag.
Among the first microwave susceptors marketed were those from the mid-1980s in a product called McCain Micro Chips, which demonstrated a susceptor sheet which cooked French fries
French fries
French fries , chips, fries, or French-fried potatoes are strips of deep-fried potato. North Americans tend to refer to any pieces of deep-fried potatoes as fries or French fries, while in the United Kingdom, Australia, Ireland and New Zealand, long, thinly cut slices of deep-fried potatoes are...
in a microwave oven
Microwave oven
A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
. These are currently used in several types of packaging for heating and cooking products in microwave ovens. Care in package design and use is needed for proper food safety
Food safety
Food safety is a scientific discipline describing handling, preparation, and storage of food in ways that prevent foodborne illness. This includes a number of routines that should be followed to avoid potentially severe health hazards....
Design
Susceptors are usually made of metallised filmMetallised film
Metallised films are polymer films coated with a thin layer of metal, usually aluminium. They offer the glossy metallic appearance of an aluminium foil at a reduced weight and cost...
, ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
s or metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
s (such as aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
flakes).