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The Way Kitchens Work
The Science Behind the Microwave, Teflon Pan, Garbage Disposal, and More
By Ed Sobey
Chicago Review Press IncorporatedCopyright © 2010 Ed Sobey
All rights reserved.
History of Aluminum Foil
Alfred Gautschi of Switzerland invented aluminum foil and was awarded a U.S. patent in 1909 (patent number 917,285). His patent claims the utility of aluminum foil for "packing chocolates and other eatables" and outlines a process for making sheets of aluminum foil that are thinner than /10 of a millimeter. The first use of aluminum foil in the United States was to protect candy, such as Life Savers. It replaced the thicker and more expensive tin foil in American kitchens in 1913.
How Aluminum Foil Works
Aluminum is a metal, and as such it is malleable — you can bend it without damaging it. It also doesn't corrode easily. Unlike iron that rusts in the presence of oxygen, aluminum is slow to react with oxygen, and when it does, it forms a surface barrier of aluminum oxide that protects the aluminum atoms below it. Kitchen aluminum foil, which is manufactured to a thickness of about 2/10 of a millimeter, protects food by keeping out oxygen, light, bacteria, and water. Other favorable properties of aluminum are its material strength and low weight, and its high heat conductivity — which means that heat passes easily through the foil. Don't wrap your body in aluminum foil before going skiing!
You will notice that one surface of aluminum foil is shiny and the other is dull. This is the result of the manufacturing process. Two sheets of foil are squeezed between rollers and later separated. The inside surfaces of both sheets are dull, but the sides that were facing the rollers are shiny.CHAPTER 2
History of the Bag Sealer
The plastics revolution brought us, among other things, thermoplastics. This family of plastics melt with the application of heat and then refreeze when they cool, making them wonderful materials for creating permanent seals.
Robert Hubbard invented a plastic bag sealer intended for kitchen use. His 1974 patent (patent number 3,847,712) mentions sealing plastic bags for "sandwiches and other food items." His patent was assigned to Dazey Products, the company that made the model that is disassembled in this chapter.
Earlier inventors had discovered a variety of ways to seal thermoplastic bags; one of the earliest is U.S. patent number 3,214,317. However, Hubbard's design appears to be the first intended specifically for home use.
How Bag Sealers Work
The model depicted in this chapter switches on when you lift the lid, but it takes a couple of minutes for the heater to warm up. Then you lay the end of the bag full of leftovers on the sealer's metal edge and close the lid. This compresses the two sides of the mouth of the bag together.
With the lid open, current flows through the heating element, a high resistance wire wrapped in a white insulator, which is under the metal edge. (For more information on how heating elements work, see the introduction, p. xiii.) When you shut the lid, a lever depresses a switch that opens the circuit, cutting power to the heating element. But by this point the edge has grown warm enough to melt the plastic on both sides of the bag, welding them together.
Some more recent models withdraw air from inside the bag to form a vacuum seal. Removing the air from a bag also removes most of the airborne spores and microbes that can spoil food. If you don't have one of these newer models, it's a good idea to squeeze the bag to rid it of air before sealing.
Inside the Bag Sealer
A safety device is wired in series with the heating element under the lid. This small device acts as a thermal fuse. If the temperature rises to an unsafe level, the fuse will open the circuit and stop the flow of electricity. The fuse contains two strips of metal that are joined together with a material that melts above 300° F. Unfortunately, the fuse cannot be reset; if it breaks, you must have it replaced.CHAPTER 3
History of the Blender
Stephen J. Poplawski invented the electric mixer in 1922 (patent number 1,480,915) to make malted milk shakes. The Hamilton Beach Company later purchased Poplawski's patents and started making his milk shake blender.
The first blender designed for home use was invented by Fred Osius in 1937 (patent number D104,289). He recruited musician Fred Waring to provide financing and marketing. The product was sold as the Waring Blendor. In 1940, Stephen Poplawski developed his own home mixer (patent number D123,509) and sold it to the John Oster Manufacturing Company. It marketed the new device as the Osterizer starting in 1946.
How Blenders Work
Electricity is supplied to the base of a blender through a switch that allows you to choose the speed of blending. The switch usually consists of mutually exclusive buttons that you depress to mix, blend, liquefy, etc. You push them and the blender makes a racket as its blades spin. As you push buttons farther to the right, the blades spin increasingly faster. Pushing different buttons changes the flow of electricity to the motor inside; the higher the voltage, the faster the motor spins.
As the motor spins, the blades hurl the contents — let's say, yogurt — toward the outside of the container walls. They force more and more yogurt outward, where it is trapped. The only way it can move is upward, so up the sides of the container the yogurt goes. Along with it go many molecules of air that are drawn into the stirring blades and pushed into the yogurt. The spinning blades pull yogurt in from above and press it out to the sides; this whirling flow of fluid is called a vortex. (Vortexes play important roles not just in blenders but also in sci-fi movies and in your bathtub.)
The powerful motor is the heart of the blender. However, equally important to its operation are the two seals that keep liquids in and out. One seal has to keep liquids in the mixing container on top. Without a reliable seal, you'd have to deal with a puddle under the container. The second seal must keep liquids out of the base of the blender so the motor and electrical controls stay dry. If this seal failed, things could get ugly. The solution is the packing seal known as the O-ring, which was patented by Niels Christensen in 1939 (patent number 2,180,795). During World War II this invention was deemed a war-critical technology, so the U.S. government purchased it from Christensen and made it available to American industry at no cost.
Inside the Blender
At the bottom of the blender's mixing container are the stirring blades. They sit atop a shaft that passes through the container and connects to a rubber or plastic coupler on the underside. Turning this coupler spins the stirrer inside. The trick in making the pitcher is allowing the shaft to turn easily without allowing liquids to leak out. This feat of engineering wizardry is accomplished with an O-ring. This rubber toroid (donut shape) fills the space between parts and expands horizontally as it is compressed vertically. As pressure is exerted on the O-ring, it forms a better seal.
The coupler on the bottom of the mixing container fits into a similar coupler on the top of the base unit. Inside the base, the second coupler is attached to a shaft, which is connected to the blender's motor. As the motor spins, it turns the couplers and thus the mixing blade. It also turns a fan inside the base unit, which draws air past and through openings in the motor to keep it cool. The motor shaft is held in place by metal bearings, one at the bottom of the shaft and one just above the fan.
The base also contains another interesting component: the blender's switches. Eight buttons control a bank of four switches. Depressing a button pushes four sliders to the right or left. These sliders, with angled cuts, lift switch arms as they slide, breaking the circuits. Otherwise, springs keep the switches in contact and the circuits closed.
Across the contacts is a 3.0-amp "general purpose rectifier." This device "rectifies" the alternating current provided through your electrical outlet, converting the cycling positive and negative current into constantly positive current and removing the variations, which provides the blender's motor with steady direct current. This allows the motor to function as a DC motor, which is much easier and less expensive to control the speed of than an AC motor. A DC motor's speed is determined by the voltage applied to it, which is how the blender switches can make the blender spin at several different speeds by increasing or decreasing the voltage.CHAPTER 4
History of the Bread Machine
The first U.S. patent for a bread machine (patent number 383,938) was issued in the late 19th century — before electricity was even available.
The modern home bread machine was invented in Japan and patented in the United States in 1985 for the Hosiden Electronics Company (patent number 4,538,509). The product was a success, which surprised many experts in the kitchen appliance manufacturing field. But once sales took off, many companies developed their own models.
The original home model included a tank so water could be added automatically and an ice box so the water could be cooled to prevent the bread temperature from rising too high. More recent models have done away with these components; thermostats are better able to control the temperature inside the machine.
How Bread Makers Work
It's ingenious that someone thought of integrating all the steps required to make bread — mixing the ingredients, kneading the dough, letting the yeast rise in a warm environment, and then baking the bread — into one tabletop device. One motor, a heating element, a timer, some switches, and a sensor are basically all that's needed to make a bread machine.
Most machines make loaves of either 1.0 or 1.5 pounds. You measure out the ingredients (flour, water, yeast, sugar, a pinch of salt) and drop them into the pan. You set the timer, and the machine takes over. A mixing paddle mixes the ingredients for a certain amount of time. Then the dough is allowed to rise: With the heating element on, the motor stops to give the yeast time to convert sugar into carbon dioxide and alcohol. The flour/water mixture becomes elastic enough to capture the carbon dioxide and form tiny bubbles throughout the bread. Next, the motor kicks on to knead the dough, letting excess gas escape. Finally, the heating element comes on to bake the bread, which also removes most of the alcohol. After the programmed baking time has elapsed, the beeper tells you it's ready.
Inside the Bread Machine
Removing a few screws allows the bread machine's metal outer cover to come off. The front control panel lifts out with its circuit board. Beneath another metal cylinder is the motor and the spindle that the mixing paddle rides on. The motor turns a large plastic geared wheel that turns the spindle above it. A rubber belt connects the motor, which sits off to one side, to the wheel.
Inside the spindle is a temperature probe called a thermistor. It has a resistor (an electronics component that resists the flow of electricity) with a special property: its resistance changes with the temperature. It sits inside the spindle so it can get an accurate reading of the temperature inside the baking loaf of bread and signal when the heating element should turn on and off. The heating element itself is a coil of high resistance wire. (For more information on how heating elements work, see the introduction, p. xiii.)
A circuit board located near the motor connects to two thermal switches. They monitor the temperature of the machine's inner metal cylinder to ensure that it doesn't overheat. The circuit board also includes the piezo speaker that bleeps at you when the bread has finished baking. (A piezo speaker contains a crystal that vibrates and makes sound when it receives a changing electrical voltage.)
At the bottom of the bread maker is a second motor. It directly drives a centrifugal fan that draws air in from beneath the bread maker and pushes it out between the machine's inner cylinder and outer cover. This is one more precaution designed to prevent the user from getting burned. Not all machines have this second motor.CHAPTER 5
History of the Can Opener
Consider this curious historical fact: tin cans were in use for nearly half a century before the can opener was invented. Based on the existing technique of preserving food in glass bottles, Peter Durand invented tin cans in 1810. The first U.S. patent for tin cans was awarded in 1825 to Thomas Kensett. The cans used then were made of thick metal. By mid-century metallurgy had improved so cans could be made of more lightweight metals. At this point, inventors turned their attention to how to better open these cans.
Does that mean that canned goods sat on pantry shelves for 45 years before people figured out how to open them? No, people were ingenious enough to open cans without dedicated openers — chisels, strong knives, or other tools were jammed into the cans to get to the food. No opener? No problem! Set the can on a rock in the fire and stand back. Eventually the can explodes, spewing beans all about and leaving half a can heated and ready to eat. (I witnessed this myself on a Boy Scout camping trip.)
Many inventors turned their attention to can openers in the mid- to late 19th century. Ezra Warner invented the first can opener in 1858 (patent number 19,063). The type of opener used today, employing a cutting wheel, wasn't invented until 1870, 60 years after canned foods were introduced. The first electric can opener was created by E. L. McCollom in 1932 (patent number 1,892,582).
How Can Openers Work
Is a lid of steel standing between you and your dinner of baked beans? Lift the can so the cutting wheel of the can opener is positioned against the inside rim of the can. Push down on the lever to drive the cutting wheel through the metal lid. Then, by hand (for nonmotorized models) or motor, rotate the can so its entire circumference passes under the cutting wheel.
The electric can opener has an electric motor that starts turning when the can opener's lever arm is pushed down. The motor rotates a serrated wheel, which in turn rotates the can under the cutting edge. Many can openers employ a magnet supported by a spring arm to grab the lid and hold it after it has been cut free from the can. Some have a knife sharpener on the back; the same motor that powers the opener turns a grinding wheel that can be used to sharpen knives.
Inside the Electric Can Opener
An electric motor constitutes about half the weight of the entire machine. On the motor shaft is a small pinion gear with teeth that are cut at an angle to the shaft. This is a spiral gear, which transmits high-speed motion with little noise or vibration. The spiral gear drives a much larger plastic gear, which shares its shaft with another small gear. That gear drives an even larger gear made of metal. This arrangement of small gears driving larger ones reduces the speed of rotation and increases the torque, or turning power. The electric motor spins way too fast to be useful without gearing, so the gears slow it down and help it deliver more turning "oomph."
The only other items of interest are the switch and cutting blade. The one-sided blade is common among can openers. It punctures the metal lid of the can while the motor rotates the can beneath it. The can opener's power switch is a simple affair. You depress the plastic button on the outside and it moves the metal arm down to the contact, which completes the circuit and energizes the motor.CHAPTER 6
History of the Coffee Grinder
Hand-turned coffee mills have been in service for centuries. The electric grinder was invented in 1907 (patent number 856,167). The inventors envisioned that it would be used for grinding both coffee and spices.
How Coffee Grinders Work
Milling or grinding coffee beans greatly increases the surface area of the coffee so the hot water can extract more of the oils that make a good, strong cup. If the milling is too coarse, the surface area of the beans will be small (relative to the volume of beans), and the low amount of oil released will make a weaker cup. But if the milling is overly fine, too much of the bean's surface will be exposed to the hot water, releasing too much oil and making the coffee taste bitter. So the job of a grinder is to break up the beans to the optimal size.
Hand-cranked mills use rotating grinders to crush the beans. Electric versions of mills (unlike grinders) spin metal blades at low speeds of 500 RPM.
Grinders run at much higher speeds; the one shown here operates at about 20,000 RPM. It cuts the beans with a two-armed blade. This design is found most often in home kitchens; it is inexpensive and works forever. However, the size of the grounds can vary greatly with this style of grinder, decreasing the quality of the resulting coffee. Burr grinders and roller grinders, which don't use the fast-spinning two-armed blades, provide more uniform grinds but are more expensive.
Excerpted from The Way Kitchens Work by Ed Sobey. Copyright © 2010 Ed Sobey. Excerpted by permission of Chicago Review Press Incorporated.
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