How Coffee Makers Work

A modern drip coffee maker is a surprisingly simple device. Manufacturers have had more than 30 years to hone their designs, so these coffee makers are pretty straightforward once you open them up.

If you take off the top of the coffee maker, you find three things:

Looking at this picture, you get your first impression that this isn't a high-tech device. If you take the bottom off the coffee maker, here's what you'll find:

The depression on the right-hand side of this figure is the bottom of the bucket. The orange tube on the top picks up the cold water coming down from the hole in the reservoir. The orange tube on the bottom is the hot-water tube (it connects to the white tube that we saw in the previous picture). You can also see the power cord coming in as well.

On the left-hand side of the base of the coffee maker is the heating element. This component is comprised of an aluminum extrusion with two parts: a resistive heating element and a tube for water to flow through. The resistive heating element and the aluminum tube heat the water. On the next page, we'll take a closer gander at what this apparatus looks like.

The resistive heating element is simply a coiled wire, very similar to the filament of a light bulb or the element in an electric toaster that gets hot when you run electricity through it. In a resistive element like this, the coil is embedded in a plaster to make it more rugged. The heating element has two jobs:

­In the picture above, you can see how the resistive heating element is sandwiched between the warming plate and the aluminum water tube. The resistive heating element presses directly against the underside of the warming plate, and white, heat-conductive grease makes sure the heat transfers efficiently. This grease, by the way, is extremely messy (very hard to get off of your fingers!). You find this grease in all sorts of devices, including stereo amplifiers, power supplies -- pretty much anything that has to dissipate heat.

The coffee maker's switch turns power to the heating element on and off. To keep the heating element from overheating, there are also components such as sensors and fuses. In coffee makers, sensors detect if the coil is getting too hot and cut off the current. Then, when it cools down, they turn the current back on. By cycling on and off like this, they keep the coil at an even temperature. Fuses simply cut the power if they sense too high a temperature. They're there for safety reasons, in the event that the main sensor fails.

Another important part of the coffee maker is the one-way valve. This valve is usually either in the hole in the bucket or in the aluminum heating pipe. If there were no one-way valve, then the boiling water would be just as likely to flow back into the bucket as to rise up the white tube. The one-way valve lets cold water into the aluminum tube, but forces the bubbles of boiling water to flow up the white tube. If you blow on the tube leading into this value, the valve should be open. If you inhale through the tube, the one-way valve should block any air.

Now that we've got the basic elements down, let's turn on the coffee maker and take it for a test drive.

All this talk of coffee got you thirsting for some java? Well, here's the lowdown on how a drip coffee maker turns a handful of grounds and a couple of cups of water into a steaming hot cup of Joe.

You can see that a coffee maker is about as simple as an appliance can get. Here's how it works:

Sounds pretty simple, right? This boiling-water pump, by the way, is the same mechanism that drives a percolator-type coffee machine. As you can see, there's no mechanical pump of any type and really no moving parts (except for the moving portion of the one-way valve). This makes coffee machines extremely reliable.

In some drip coffee makers, there are also different advanced features that give you more control over your coffee. On the next page, we'll learn about them, as well as what happens when disaster strikes and the coffee maker goes out of commission.

­You're groggy. The sky still looks the same as when you started snoozing the night before and you stumble into the kitchen gung-ho to flip that magic switch. But what's this? You turned it on and nothing happened. No cheerful gurgling, no promising rumbling. No coffee!

Here are some of the most common problems that can cause your drip coffee maker to stop working:­

There are two problems that are nearly impossible to fix: failure of one of the heat-sensitive switches and failure of the heating coil. Because it's very challenging to get replacement parts, you'll probably have to buy a new coffee maker if one of these problems disables your machine.

­Assuming no calamity has struck your coffee maker, what are some of the advanced features it might offer? Well for starters, many have a programmable timer, meaning you can get everything ready the night before and when your alarm clock starts beeping, the coffee pot starts gurgling. By the time you roll out of bed and trudge to the kitchen, your coffee is ready and waiting. In some machines, a built-in grinder means that cup of coffee will also be nice and fresh, ground just before brewing began. Another interesting feature available is the ability to pause in the middle of a brewing cycle. This way, if you're the first one out of bed making coffee for an entire household, you can grab your first cup before the entire pot is prepared.

Many digital drip coffee makers also allow you to adjust the strength of the brew -- if want a stronger cup of coffee the brewing time slows to accommodate. Some also have self-cleaning cycles and filtration systems. Freshness counters can let you know how long a pot of coffee has been sitting out and automatic shut-off features can ease fears that you forgot to turn the cof­fee maker off when you left for work.

Now, when you make coffee tomorrow morning, you can do so with a new appreciation for exactly what's happening inside. For more information on coffee makers, coffee and related topics, check out the links on the next page.