How Are Coffee Filters Made?
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History
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Before learning about how coffee filters are made, it is important to know why they are made. Before the 20th century, coffee was often made in a percolator, and the grounds were sometimes filtered through a linen bag as they brewed. This was not an ideal method, since the linen would fail to trap many of the grounds, which ended up in the drinker's cup. Also, once the linen became stained, it was very difficult to clean. In 1908, a German woman named Melitta Bentz discovered a new way to brew coffee. She used a nail to perforate the bottom of a brass pot and lined it with some blotting paper from one of her son's school books. The paper served as a superior filter to linen, as it was cheap, disposable and kept all the grounds out of the brewed coffee, cutting the bitterness of the drink. Mrs. Bentz had invented the modern paper coffee filter.
Properties of Paper
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Today, paper coffee filters have not changed much from the school blotting paper used by Melitta Bentz in 1908. Its advantages still hold true, and it is by far the most common type of coffee filtration material in use. The chief properties of paper coffee filters are their porosity and the length of the wood fibers in the raw pulp. Coffee filters are made from softwood harvested from fast-growing trees like pine. The length of the wood fibers creates a sort of latticework in the structure of the paper that is porous enough to allow the coffee to soak through, but strong enough to block the flow of coffee grounds. The sides of a coffee filter are crêped in order to allow the coffee to flow smoothly from the filtration funnel. While all paper coffee filters are made from the same basic materials, there are a few variations. Different sized filters are made to fit different coffee makers, and the paper itself can be bleached white or sold in a natural brown color. The color of the paper, however, has no effect on its filtration ability.
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Stainless Steel Filters
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Indian filter coffee is not made with a paper filter. Instead, it is brewed through a stainless steel filtration cup. Coffee grounds are placed inside the cup, which has a perforated bottom. They are then gently pressed until they form a disc covering the entire bottom of the cup. The filtration cup is placed over a tumbler, and boiling water is poured inside. The filtration cup is covered, and the water soaks through the coffee grounds, through the holes and into the tumbler below. The resulting coffee is quite strong, so it is usually mixed with steamed milk.
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