howstuffworks _inside a coffee maker

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How Coffee Makers Workby Marshall Brain and Jessika Toothman

Browse the article How Coffee Makers Work

This basic drip coffee maker mightnot have lots of bells and

whistles, but it can definitely whipup a quick cup of coffee.HowStuffWorks 2008

A look into a drip coffee maker proves it's a fairly basic gadget.HowStuffWorks 2008

How Coffee Makers Work

Most people who are dependent on caffeine have breakfast with an old friend -- the coffee maker. Every morning you scoop in

the coffee, add some water and flip it on, but have you ever wondered what's happening inside. How does the water get from

the reservoir over to the coffee grounds in the filter basket? How does everything heat up so quickly, and what on earth is that

gurgling noise?

In this article, we'll look inside a typical drip coffee makerso you can understand exactly what's happening when you make

coffee. We'll also look at the possible problems that might cause your coffee maker to stop working. By the end of this article,

you may look at your old friend in a completely new way.

Before we get into that, however, let's do a quick coffee rundown. Coffee plants are evergreen tropical shrubs and small trees,

and they grow best between the Tropic of Cancerand the Tropic of Capricorn (often referred to in the coffee world as the

Bean Belt) which makes sense because the plants enjoy lots of rain and gentle temperatures. Coffee beans as we know them

are actually the seeds of the fruit of the coffee plant -- called coffee cherries -- and these popular plants have been cultivated

by man for hundreds of years. The two most commonly grown species of coffee plants are Coffee arabica (Arabica coffee)

and Coffea canephora (Robusta coffee). For more about details about what's in your morning cup, check out the article How

Coffee Works.

There are lots of coffee makers on the market that can arguably make a better pot of Joe, but in this article, we'll be focusing

on the trusty drip. If your tastes do run fancier, check out the article How the Clover Coffee Maker Works. On the other hand,

if you're gunning for an insider's look at your kitchen's appliance of the year, we'll crack it open and take a peek on the next page.

Inside a Coffee Maker

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:

There's a reservoirthat holds the water when you pour it into the pot at the start of the

coffee-making cycle (on the right in the picture above). At the bottom of the bucket there's ahole, and its role will become obvious in a moment.

There's a white tube that leads up from below the reservoir base, carrying the hot water

up to the drip area.

There is a shower head (on the left-hand side of the picture). Water arrives here from the

white hot-water tube and is sprayed over the coffee grounds. In some coffee makers, the

water comes out of the hose onto a perforated plastic disc called the drip area and simply

falls through the holes into the coffee grounds.

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

Launch Video

How to Make Coffee in a Coffee Maker

StuffWorks "Inside a Coffee Maker" http://home.howstuffworks.com/coffee-maker1.htm

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Things are about to start heating up!HowStuffWorks 2008

The heating element efficiently serves dual functions.HowStuffWorks 2008

The various sensors and fuses of this coffee maker likely lie in the whitesheathing bridging the heating element.HowStuffWorks 2008

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 Heating Element of Coffee Makers

The resistive heating element is simply a coiled wire, very similar to the filament of a light

bulb or the element in an electric toasterthat gets hot when you run electricity through it. In

a resistive element like this, the coil is embedded in a plasterto make it more rugged. The

heating element has two jobs:

When you first put the water in the coffee maker, the heating element heats it.

Once the coffee is made, the heating element keeps the coffee warm.

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.

Making Coffee

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:

When you pour in cold water, it flows from the reservoir through the hole and into the


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Sleepy? A cup of HowStuffWorks coffee can get you going.HowStuffWorks 2008

orange tube.

Then the water flows through the one-way valve, into the aluminum tube in the heating

element and then partially up through the white tube. This all happens naturally because of

gravity.

When you turn on the switch, the resistive heating element starts heating the aluminum

tube and eventually the water in the tube boils.

When the water boils, the bubbles rise up in the white tube. What happens next is exactly

what happens in a typical aquarium filter: The tube is small enough and the bubbles are big

enough that a column of water can ride upward on top of the bubbles.

The water flows up the white tube and is dispersed to drip evenly on the waiting coffee grounds.The hot water flows through the ground coffee beans, picking up their oil essence on the way down into the coffee pot. This coffee oil, released during the

roasting process, is called caffeol.

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.

Drip Coffee Maker Problems: What Can Go Wrong with Your Coffee Maker?

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:

The power cord or on/off switch can go bad. In either of these cases, it's best to get a pro to replace it or buy a new coffee maker -- replacing it improperly

can lead to a fire.

The one-way valve can get clogged open or closed . You can usually fish out the debris that causes this problem with a toothpick.

The tubes can get clogged with calcium. This is especially true of the aluminum heating tube. The normal way to solve this problem is to run vinegar through

the machine once, and then run two batches of water through to clean out the vinegar.

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.

Lots More Information

Related HowStuffWorks Articles

How Coffee Works

How Espresso Machines Work

How Espresso Works

How Caffeine Works

How Nicotine Works

Small Appliance Basics

How to Clean Small Appliances

How to Repair Small Appliances

How are coffees, teas and sodas decaffeinated?

Why does caffeine keep you awake?

More Great Links

Association for Science and Information on Coffee


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Coffee Science Source

CoffeeResearch.org

International Coffee Organization

National Coffee Association of the United States

Sources

"All About Coffee." National Coffee Association of U.S.A., Inc. (10/31/2008) http://www.ncausa.org/i4a/pages/index.cfm?pageid=30

"Automatic Drip Coffee Makers Reviews and Prices." HowStuffWorks.com Consumer Guide. (10/31/2008) http://products.howstuffworks.com/automatic-

drip-coffee-maker-reviews.htm

Beller, Deborah. "How Coffee Works." HowStuffWorks.com. (10/31/2008 http://recipes.howstuffworks.com/coffee.htm

Coffee Research Institute Web site. (10/31/2008) http://www.coffeeresearch.org/about/overview.htm

"Coffee." Encyclopedia Britannica. (10/31/2008) http://www.britannica.com/EBchecked/topic/124337/coffee

"Coffee." National Geographic. (10/31/2008) http://www.nationalgeographic.com/coffee/

"How does a stovetop coffee maker work?" WiseGeek.com. (10/31/2008) http://www.wisegeek.com/how-does-a-stove-top-coffee-maker-work.htm

"What is a coffee maker?" WiseGeek.com. (10/31/2008) http://www.wisegeek.com/what-is-a-coffee-maker.htm

International Coffee Organization Web site. (10/31/2008) http://www.ico.org/index.asp

"Roasting/Making Coffee." International Coffee Organization. (10/31/2008) http://www.ico.org/making_coffee.asp

"What is a French press?" WiseGeek.com. (10/31/2008) http://www.wisegeek.com/what-is-a-french-press.htm


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