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HowStuffWorks 2008

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 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.