A coffee filter is a coffee

Coffee

Coffee is a brewed beverage with a dark,init brooo acidic flavor prepared from the roasted seeds of the coffee plant, colloquially called coffee beans. The beans are found in coffee cherries, which grow on trees cultivated in over 70 countries, primarily in equatorial Latin America, Southeast Asia,...

-brewing utensil, usually made of disposable paper. A stainless steel

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

 filter is used to prepare Indian filter coffee

Indian filter coffee

South Indian Coffee, also known as Filter Coffee is a sweet milky coffee made from dark roasted coffee beans and chicory , especially popular in the southern states of Karnataka and Tamil Nadu...

, the form of coffee common in India.

Paper filters remove oily components called diterpenes; these organic compounds, present in unfiltered coffee, appear to increase the risk of coronary heart disease. Metal or plastic mesh filters do not remove these components.

History

On July 8, 1908, the first paper coffee filter was created by German housewife named Melitta Bentz

Melitta Bentz

Amalie Auguste Melitta Bentz , born Amalie Auguste Melitta Liebscher, was a German entrepreneur, who invented the coffee filter in 1908.-Biography:Bentz was born in Dresden, Germany...

. She wanted to remove the bitter taste caused by boiling loose grounds or using the typical method of linen to brew coffee.

Paper filter

Coffee filters of paper

Paper

Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....

 are made from about 100 g/m² crêpe paper

Crêpe paper

Crêpe paper is tissue paper that has been coated with sizing and then creped to create gathers.-Production:Paper that is creped is produced on a paper machine that has a single large steam-heated drying cylinder fitted with a hot-air hood. The raw material is paper pulp. The Yankee cylinder is...

. The crêping allows the coffee to flow freely between the filter and the filtration funnel

Funnel

A funnel is a pipe with a wide, often conical mouth and a narrow stem. It is used to channel liquid or fine-grained substances into containers with a small opening. Without a funnel, spillage would occur....

. The raw materials (pulp

Pulp (paper)

Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...

) for the filter paper are coarse long fiber

Softwood

The term softwood is used to describe wood from trees that are known as gymnosperms.Conifers are an example. It may also be used to describe trees, which tend to be evergreen, notable exceptions being bald cypress and the larches....

, often from fast growing trees. Both bleached

Bleaching of wood pulp

Bleaching of wood pulp is the chemical processing carried out on various types of wood pulp to decrease the color of the pulp, so that it becomes whiter. The main use of wood pulp is to make paper where whiteness is an important characteristic...

 and unbleached qualities are made.

Typically coffee filters are made up of filaments approximately 20 micrometres wide, which allow through particles less than approximately 10 to 15 micrometres.

For a filter to be compatible with a coffee maker, the filter needs to be a specific shape and size. Common in the United States are cone-shaped filters #2, #4, and #6, as well as basket-shaped filters in an 8-12 cup size.

Other important parameters are strength, compatibility, efficiency and capacity.

If a coffee filter doesn't possess enough strength, it will tear or rupture, and many of the coffee grains will collect in the coffee pot. Compatibility describes a filter medium's resistance to degradation by heat and chemical attack; a filter that is not compatible with the liquid passing through it is likely to break down, losing strength (structural failure

Structural failure

Structural failure refers to loss of the load-carrying capacity of a component or member within a structure or of the structure itself. Structural failure is initiated when the material is stressed to its strength limit, thus causing fracture or excessive deformations...

). Efficiency is the retention of particles in a target (size) category. The efficiency required is dictated by the particles or substances trying to be removed. A large-mesh filter may be very efficient at retaining large particles, but inefficient at retaining small particles. Capacity is the ability to "hold" previously removed particles while allowing further flow. A very efficient filter may show poor capacity, causing increased resistance to flow or other problems as it plugging up prematurely and increasing resistance or flow problems. A balance between particle capture and flow requirements must be met while ensuring integrity.