By Randy D. Pope
Coffee wasn’t always filtered. Originally, coffee was brewed by boiling water with ground coffee, then pouring off the beverage, trapping the grounds in a corner. Obviously this was a less than effective way to keep the grounds out of the coffee, and as a result, before 1908, a person quaffing a cup of coffee probably enjoyed some coffee grounds with the liquid.
All this changed in 1908 when a housewife from Dresden, Germany, Melitta Bentz, punctured the bottom of a brass pot and lined it with blotting paper. The result – the first filter-drip coffee. According to the Melitta website, she patented the device, now named "Filter Top Device lined with Filter Paper" which took on a cone shape in the 1930s, creating a larger filtration area lined with ribs for improved extraction of the ground coffee.
Then in 1957, the owner of a fledgling coffee brewer manufacturing business in the USA began experimenting in his Springfield, Illinois kitchen. Frustrated with cone and cloth filters, George Bunn developed the flat-bottom, fluted paper filter for use in commercial coffee brewers in the early 1960s.
Why filter coffee?According to Ted Lingle’s Coffee Brewing Handbook, filters should provide a level bed for coffee. Both Specialty Coffee Association of America (SCAA) and the Speciality Coffee Association of Europe (SCAE) recommend a level bed of one to two inches of dry grounds for coffee brewing, assuming that the coffee will expand about 50% during brewing. Using a flat-bottom filter and a flat-bottom basket in the coffee brew funnel is a good way to assure this. A wire form or plastic ribs in the coffee brew basket generally supports the filter and coffee grounds. A filter also provides multiple points of drainage for the water and allows proper water flow rate.
The most important role played by coffee filters is removal of oil and undissolved solids from the final beverage, Lingle says. Depending on beverage, you may want to remove almost all of the oils and solids, as in the case of instant coffee. On the other hand, Turkish coffee is not filtered, and this is acceptable to those who choose this beverage. The amount of filtering depends on the final beverage, as well as the individual preference of the drinker. "The type of filter directly affects the body of the finished brew, which, in turn, affects the flavor of the beverage. The body is created by the soluble materials,… that are rinsed off of the coffee particles. These insoluble materials create brew colloids, which trap soluble flavoring materials and gases in the brew," according to Lingle. "The colloids break apart as you drink coffee, simultaneously releasing the aromas in your palate as the brew reaches your taste buds," he explains.
I believe that in the US, coffee drinkers have the expectation that no undissolved solids will be present in the coffee. TDS or total dissolved solids are just that – dissolved. However, the amount of solids and oils in the coffee is very much a matter of individual preference, and that is why a variety of filters are used.
There are three basic types of coffee filters: metal, cloth and paper.
Metal filtersAn example of a metal filter, a portafilter, is used when brewing espresso. Most portafilters let a certain amount of coffee sediments into the beverage, but espresso drinkers accept this. It is all part of the espresso drinking experience.
Filter drip coffee aficionados have a different expectation though the beverage they enjoy must be free of grounds. Although oils and dissolved solids contribute to the flavor of the beverage, sediment is not an acceptable component of most filter drip coffee. The sole exception is coffee brewed in French press pots or cafetières. These pots contain mesh screens that act as filters. Some sediment makes it through the filter into the coffee, and that’s why French press coffee tastes best served piping hot and fresh. Any time fibrous material is introduced into a beverage, it breaks down more quickly and plays a central role in the rapid deterioration of the flavor of coffee made in a French press.
Metal filters are widely available, especially online, and some consumers prefer the flavor of coffee made with these filters. They are used to the sediment load and mouth feel of the coffee, and accept it as a part of the beverage. Chrome, brass and stainless steel are plated and widely used as a metal filter material. Metal filters are reusable, but they must be emptied and rinsed after each use, then cleaned daily with a brush and mild detergent.
Cloth filters
Originally made of unbleached muslin, cloth coffee filters are more effective than metal filters in reducing the amount of solids passed into the beverage, while still allowing many of the oils in coffee through. Environmentally friendly, cloth filters come in a variety of sizes and are washed after each use. Because of the maintenance issue, cloth filters have passed out of popularity in the coffee community.
Paper plays a very important role in the effectiveness of a paper filter. The overall tensile strength of the filter changes depending on whether the filter is dry or wet. A dry filter must be strong enough to maintain its shape and structure: wet, the filter must stand up during brewing and not collapse under the weight of the grounds. The specifications for filter paper are generally closely held and not released by filter manufacturers. The crepe of the surface depends on the type of paper.
The "crepe" or roughness of the paper’s surface plays a big role in its effectiveness as a coffee filter. This has to do with the paper’s graded density or the tightness of the fibers throughout the paper. The tightness of the fiber varies from the inside to the outside edge of the filter.
Many paper filters now have flutes or ridges on the filter sides. Flutes play a number of roles. First, they provide rigidity to the side of the filter to help it stand up. Flutes also prevent the filter from adhering to the smooth surface of the brew basket so that the water can move through the filter. The number of flutes in the filter depends on its size: 12 cup filters may have 24 flutes while larger filters have 36 or more.
Whitened vs natural colorationThere is an ongoing debate about the value of filters that have been whitened versus those which have a "natural" coloration. Again, this is a matter of personal preference. I like to do a test where I put a filter of each type into a clear glass of hot water. Within a minute or so, the color of water in the glass with the unwhitened filter has taken on a slightly yellow tinge and you can smell the paper pulp. If you can smell something you can taste it. To me, that means that the taste and color of the beverage brewed with this filter will be affected.
Filter paper can be whitened through a variety of processes: totally chlorine-free, process chlorine-free, and elemental chlorine-free. According to the website for the Reach for Unbleached Foundation (www.rfu.org) TCF, or Totally Chlorine-Free, signifies virgin pulp (not recycled) that has been bleached with no chlorine compounds. PCF, or Process Chlorine-Free, indicates that a product is made with recycled fibers and that no chlorine compounds have been used in the recycling process. ECF, or Elemental Chlorine-Free, is … pulp bleached without "elemental" chlorine gas….
In addition, processes such as oxygen whitening and ozonating can be used to further whiten paper. Any filter paper that comes in contact with food must be approved by the United States Food and Drug Administration.
A word about tea filtersLong leaf teas don’t require a filter for steeping, but if fannings and dust are used, a filter is necessary to keep solids out of the beverage. Iced tea brewing often uses this type of tea, and so a paper filter is recommended, however because it breaks down quickly, hot tea is brewed in smaller volumes -- pots or single servings. Often tea is packaged in tea bags, which acts as a natural filter.
A good filter is an important element in brewing perfect coffee or tea. Make sure you understand a filter’s role in these wonderful beverages.
Author Randy D. Pope is director, BUNN Beverage Technology Center