The burner assembly is the basic unit in a gas-fired piece of equipment that mixes gas with oxygen and thus produces the heat required for cooking. Today there are many different types of burners, each designed to meet the demands of a particular appliance. All burners have ports, a series of round holes from which the flames burn. There are wide and narrow ports, and they can be arranged in various patterns (see Illustration 6-4). A few of the most common burner types are discussed next.
Pipe Burner.
This is a pipe (usually made of cast iron) with two or more rows of ports drilled along its length. You’ll find pipe burners in ovens, griddles, and broilers. Although most pipe burners are straight, there are also loop burners, in which the pipe has been bent into a circular or oval shape.Ring Burner.
These are widely used on range tops, steam tables, boilers, and coffee urns. The standard ring burner has one or two rows of ports arranged in a circle. It’s made of cast iron and comes in a variety of sizes. To increase the capacity of a burner, several ring burners of different diameters can be nestled one inside the other so that one, some, or all of them can be turned on as needed. Some ring burner ports face side-ways instead of straight up, so that food cannot be spilled into them accidentally.ILLUSTRATION 6-4 Gas burners come in several different shapes and sizes.
ILLUSTRATION 6-3 The four most hazardous gas flame conditions, all of which require adjustment.
Source: Anne Marie Johnson, Cooking for Profit (Robert Hale, Ltd., London, UK,1991).
Ring burners are sometimes known as atmospheric burners, because the secondary air comes from the atmosphere around them. However, the flame tips often suck in too much oxygen, making them less efficient and requiring frequent adjustment of the primary air-gas mixture.
Slotted Burner.
This is really a type of pipe burner, because it is made of the same cast iron pipe and can be straight or circular. The ports in a slotted burner are all aimed in the same direc-tion to form a single, large flame. Some have only one wide slot, with a corrugated ribbon of heat-resistant metal alloy located inside the slot to allow a wider ( but still safe) path for the flame. Slotted burners are typically found in hot-top ranges and deep-fat fryers.Flame Retention Burner.
This is a slotted burner with additional ports drilled into the pipe. It allows more heat to flow into the burner, improves combustion, and reduces flashback.Flame retention burners are considered very efficient, with a wide range of heat settings and the ability to fine-tune your primary air adjustment.
Radiant (Infrared) Burner.
The usual infrared burner is a set of porous ceramic plates, with about 200 holes per square inch on its surface. Air and gas flow through these holes and burn very hot (about 1650 degrees Fahrenheit), which makes this type of burner ideal for broilers. They can be located at the sides of a fry kettle for maximum heat transfer or suspended inside a protective cylinder located at the bottom of the fry tank.Fryers with infrared burners boast 80 percent energy efficiency, compared to about 47 percent for conventional fryers. Their heat recovery time (the time it takes to return to optimum cooking temperature after a new batch of cold food has been loaded into the ket-tle) is less than two minutes. The same benefit—heat intensity—makes the infrared burner popular for griddles. A sturdy, one-inch-thick griddle plate can be used instead of a thinner one that is not able to retain heat as well.
Infrared burners work so well because they use radiant heat, and the best example of radiant heat is the sun. Have you noticed how the sun can warm your face on a winter day, even though the air around you is cold? In the same way, the infrared burner sends its high-frequency waves directly from the heat source to the food. The rays only turn into thermal (heat) energy when they hit the food; they do not heat the air. When you’re cooking, you get the most energy efficiency from an appliance that heats the food, not the air that surrounds it.
Range-top Power Burner.
This burner premixes gas and combustion air in correct proportion to produce high heat and efficiency. Unlike the standard ring burner, the power burner does not rely on the atmosphere to supply its secondary air. The burner head is enclosed in a sealed metal ring through which no excess air can enter. Flames are spread evenly through the ring over the bottom of the cooking pot, so less heat is wasted, more heat is delivered to the food, and the kitchen stays cooler. The burner head acts as a shutter mechanism, readjusting the premixed air and gas whenever the controls are turned up or down.A recent appliance development is the power burner range, with two (front) power burn-ers and two (back) conventional burnburn-ers, the front ones for speedy cooking and the back ones for keeping food warm.
Infrared Jet Impingement Burner.
The IR jet, as it’s known, is a type of high-efficiency burn-er that also uses less gas than conventional burnburn-ers. It is a powburn-er burnburn-er that premixes gas and air in a separate chamber before burning. This mixture is fed into the burner by a blow-er and ignited at the burnblow-er surface. The pblow-erforated cblow-eramic burnblow-er plate holds the flames in place and allows them to impinge (hit hard) on the bottom surface of the pan.Pilot Lights and Thermostats.
The pilot light is an absolute necessity in the gas-fired commer-cial kitchen. There are several different kinds of pilot lights, some automatic and some manual, and most gas appliances make it possible for you to easily adjust the pilot light, if necessary, with the turn of a screw. Illustration 6-5 shows the inner workings of the two mostcommon types of gas pilot lights. The newest technology, however, replaces the gas pilot with electronic spark ignition of the gas flame, reducing gas consumption because the pilot doesn’t have to stay con-tinuously lit.
The standard gas pilot light should be about three-quarters of an inch high. This small flame is located next to the main burners of the appliance. In some cases, there’s a separate pilot for each burner; in others, a single pilot light is used to light more than one burner.
If the pilot light goes out, it is a signal that the gas has been shut off. Like other gas flames, pilots can also burn yellow, which means dirt or lint may be blocking the opening. You can remove the dirt by brushing the orifice clean again.
Pilot lights have safety features, the most common of which is the thermoelec-tric control. When a junction of two metal wires (called a thermocouple) is heated by the pilot flame, a very low electric voltage is generated—just enough to fire an elec-tromagnetic gas valve and hold it in an open position. If the pilot light fails, the
thermocouple cools, the electric current stops, and the gas valve is closed by spring action.
To resume the flow of gas, the pilot must be manually relit.
The thermostat is the control used on most gas-fired equipment to maintain the desired burner temperature. By far, the most common thermostat is a knob or dial called a throttling or modulating control. It allows the flames to rise or fall quickly, then regulates the gas flow to keep the burner temperature constant.
Some types of cooking appliances, such as deep-fat fryers, require quick heat recovery in less than 2 minutes. In these cases, a snap-action thermostat is used, which opens fully to permit maximum heating until the desired temperature is reached. Then it shuts off just as quickly.
Remember that the function of a properly working thermostat is to turn down, or shut off, the supply of gas as soon as the burner reaches the desired temperature. Should you need to reduce the burner’s temperature, turning down the thermostat will not be sufficient.
There’s already heat stored in the appliance, and it will take time for it to dissipate and cool down. On a gas oven, for instance, you should set the thermostat to the new, lower level and then open the oven doors to allow it to cool more quickly.
When you need to raise the temperature (e.g., starting the oven when it’s cold), many people have the mistaken impression that the appliance will heat more quickly if you blast it immediately to “High” and then turn it down. In fact, it won’t heat any faster, and you risk forgetting to turn it down and damaging the food by cooking it at an excessive temperature.