Drip brewing, or filtered coffee, is a method which involves pouring water over roasted, ground coffee beans contained in a filter, creating the beverage called coffee. Water seeps through the ground coffee, absorbing its oils and essences, solely under gravity, then passes through the bottom of the filter. The used coffee grounds are retained in the filter with the liquid falling (dripping) into a collecting vessel such as a carafe or pot. Paper coffee filters were invented in Germany by Melitta Bentz in 1908 and are commonly used for drip brew all over the world. In 1954 the Wigomat, invented by Gottlob Widmann, was patented in Germany being the first electrical drip brewer. Drip brew coffee makers replaced the coffee percolator in the 1970s due to the percolators’ tendency to over-extract coffee, thereby making it bitter. One benefit of paper filters is that the used grounds and the filter may be disposed of together, without a need to clean the filter. Permanent filters are now also common, made of thin perforated metal sheets or fine plastic mesh that restrain the grounds but allow the coffee to pass, thus eliminating the need to have to purchase separate filters which sometimes cannot be found in some parts of the world. These add to the maintenance of the machine, but reduce overall cost and produce less waste. Drip brewing is a widely used method of coffee brewing, particularly in North America owing to the popularity of domestic coffeemakers. There are, however, several manual drip-brewing devices on the market, offering a little more control over brewing parameters than automatic machines, and which incorporate stopper valves and other innovations that offer greater control over steeping time and the proportion of coffee to water. There also exist small, portable, single-serving drip brew makers that only hold the filter and rest on top of a mug or cup. Hot water is poured in and drips directly into the cup. Brewing with a paper filter produces clear, light-bodied coffee. While free of sediments, such coffee is lacking in some of coffee’s oils and essences; they have been trapped in the paper filter. Metal filters do not remove these components. It may be observed, especially when using a tall, narrow carafe, that the coffee at the bottom of the coffeepot is stronger than that at the top. This is because less flavor is available for extraction from the coffee grounds as the brewing process progresses. A mathematical argument has been made that delivering comparable strength in two cups of coffee is nearly achieved using a Thue-Morse sequence of pours. This analysis prompted a whimsical article in the popular press. A less familiar form of drip brewing is the reversible or “flip” pot commonly known as Napoletana.