How Does a Percolator Work?
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History
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Coffee has been brewed and enjoyed since the 5th century, but the first coffee cafes did not open until the 17th century. It was at that time that coffee aficionados realized that they needed a better way to brew coffee. A metalsmith in Paris first developed the percolator in 1819, and percolators are still used to brew coffee to this day. However, percolating is one of the least favorite methods used to make a cup of coffee as the resulting coffee is usually extremely hot and bitter.
Parts of a Percolator
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There are five parts to a percolator: a pot, a stem, a filter basket, basket cover and pot lid. The stem is a hollow tube that fits into the bottom of the coffee pot. The filter basket then fits onto the tube, and the basket cover, a perforated lid, fits on top of that. Lastly is the coffee pot lid, which sometimes contains a glass bubble. The lids with these glass bubbles show the coffee coming up from the tube and splashing back down into the pot.
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The Percolating Process
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Ground coffee is placed onto the filter basket, which is attached to the stem in the pot. Water is then added to the pot and heated to a boil. When the water boils, it flows upward through the stem. When it reaches the filter basket lid, it is dispersed downwards onto the coffee grounds in the filter basket. The coffee then drips from the basket into the pot of water below, and the process starts all over again.
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The magic that makes the water defy gravity is the disk which is at the bottom of the tube. When heat is applied to the pot, the disk keeps that heat from warming the entire volume of water; only the water under the disk is heated, the rest of the water stays cool. When the water under the disk boils, the bubbles of steam rise through the stem, due to their buoyancy. Because the stem is skinny, the steam bubbles cannot go around the water that's inside the stem, and must instead push that water upwards. Because nature abhors a vacuum, each bubble that rises through the stem pulls unboiled water into the space below it. Because the stem is made of metal, the alternating water blobs and steam bubbles are cooled by the water which surrounds the stem. Because of this, even though the steam bubbles have a temperature of 212F, the water between the bubbles is cooler. When the water and steam reach the glass knob, the steam leaves the percolator, and the water passes through the coffee grounds. When the brewed coffee drips out, it lands on top of cool water. Since heat rises, the hot coffee sits on top of the cool water, with minimal mixing. Eventually, all of the cool water is used up, and the brewed coffee reaches the disk. If the percolator isn't removed from heat immediately at this point, the brewed coffee then boils, and the flavor is destroyed. If the water wasn't cold enough to start with, not enough cooling of the water will occur as the water rises through the stem, resulting in over-extraction. If the disk is metal, instead of plastic or ceramic, heat will pass through it and warm the water which is supposed to remain cool, which reduces the ability of that water to cool off the water and steam rising through the stem; this also can cause over-extraction. Worse, this can also cause the unbrewed water to mix with the brewed coffee, resulting in brewed coffee passing under the disk, resulting in boiled coffee. If your percolator makes nasty coffee, try starting with colder water.
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Well, it's clear you people are no help. ;-)
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and don't even get me started about the thermos. I mean you put hot things in, it keeps them hot. You put cold things in it keeps them cold. How does it know which to do?
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If you live a while with a south Italian family and have coffee from their seriously old and "dirty" percolator it tastes perfectly fine...
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Really depends on the percolator ;)
