Hobs - Did you know?

The hob is used for boiling, frying, steaming, simmering and braising. It primarily works by the conduction of heat from the flame through the pan surface. A certain amount of radiant heat is also generated. A large volume of primary air is provided so that the pan can be located as close as possible to the burner head and so gain the heat from the flame. The flame should not be allowed to lick up the side of the pan as heat will be wasted. 

The hotplate is usually a solid steel flat plate or ceramic surface, on which the pan sits, or it can take the form of a griddle, which is used for dry-frying foods such as eggs etc. The flame is located beneath the metal and heats it to the desired temperature.

The heat setting of a hob or hotplate often has a grading, such as simmer, medium and high. The flame does not adjust to the heat requirements of the food being cooked and if set too high, the contents of the pan may boil over or burn. Some appliances have thermostatically controlled burners. They work using a contact sensor that is filled with a volatile fluid that, when heated, expands forcing the gas valve to close down to a by-pass rate. With freestanding cookers all control taps and the oven thermostat are located on a pipe, named the float rail, which is located behind the control knob fascia. During any maintenance work all these gas connections should be sprayed with leak detection fluid to ensure they are gas tight. The gas burners used with the associated parts of the cooker are generally unprotected, in terms of flame failure. This means that should the flame go out, gas is allowed to discharge freely into the room. The oven will be found to have a flame failure device fitted, usually of the liquid vapor type, which will shut down the main flow of gas but will still allow a discharge through the by-pass. Cookers supplied by LPG are controlled and all control taps generally require the operation of a thermo-electric FSD before gas is allowed to flow freely. 

The Grill - did you know

The grill is used for toasting, grilling or browning previously cooked food. It works

by directing radiant heat that has been produced on the surface of a red-hot fret,

mesh or gauze surface, on to the food. There are two designs of grill.

First, those referred to as conventional grills, as they have been around the longest.

The grill consists of a pressed steel burner, fed via an injector at one end and located

beneath an expanded metal fret. The flames, on leaving the burner, heat the metal fret

and cause it to glow red-hot. The combustion products rise by convection through

holes in the canopy top. The biggest problem with this design is the problem of

uneven cooking, a result of the burner failing to heat the whole surface of the fret

uniformly.

In the second design of grill, known as a surface combustion grill, the injector feeds gas

into the primary air intake, this entails some 80–90% of that required for combustion.

The mixed gas and air now travels to the centre of a sealed chamber, which has a fine

metal mesh burner surface where the ignition probe is located and where combustion

takes place, the air/gas mixture clings to its face, producing an evenly heated radiant

surface across the entire burner.

Deep Fryers - Did you know

 Deep fryers:

These are appliances that hold a quantity of oil or fat in which food such as chips, fish and doughnuts are cooked. There are two different designs - one that has a flat bottom with the oil heated directly from below and a second type has oil that is heated at a location above the base so maintaining a cool zone below the flame in which old food particles can sink without carbonizing and spoiling the flavor of the food load. There are two methods of heating the oil using this design of fryer. In the first method there is what is known as a V-shaped fryer, with the lower V section below the burner. The second method requires the gas flame to be fired directly into tubes that pass through the mass of the oil. With the flat bottom fryer it is essential that, before each frying all old particles are strained from the oil. The heat input can vary between 8 kW and 40 kW depending on the size of fryer.

Grill and Salamanders - Did you know

Grill and Salamanders

Under-fired or flare grills give a heat source below the food, operating up to 30 kW. The grill consists of a burner firing upwards on to a bed of refractory ceramic or pumice material. The food is placed on a series of bars. As the hot fat from the food drops, it is burnt off in the form of an ‘uncontrolled’ flame, giving the meat a characteristic appearance and flavor. 

Horizontally fired grills use surface combustion plaques between 3 kW and 12 kW and are often accompanied by a rotisserie to cook food. The fat from the food can drop to be collected in a container at the base. Over-fired grills or salamanders have the heat source above the food and operate between 5 kW and 16 kW. They can also be used for toasting. This type of grill often has a grooved solid aluminum branding plate on to which the food is placed. This plate allows the hot fat to drain away but at the same time assists in cooking the food on both sides due to absorbed heat that is held in the aluminum plate.

Salamander

Grill

Thermocouples: What are they?

                                                               Thermocouples

The thermocouple is a vital safety feature for many gas appliances. A thermocouple uses the heat from a flame to produce a millivoltage that controls a gas valve. If the pilot goes out, the thermocouple can no longer send the millivoltage that is required to allow the gas valve to stay open, thus sealing the valve to prevent a dangerous gas leak.

Thomas Johann Seebeck accidentally discovered the Thermocouple in 1821. He experimentally determined that a voltage exists between the two ends of a conductor when the conductor's ends are at different temperatures. His work showed that this voltage is proportional to the temperature difference. His discovery soon became the basis of the thermocouple, which today is one of the most popular and cost effective temperature sensors.