Filter Coffee
The fundamental principle of filter coffee is simple: a basket, usually conical, lined with a porous filter. Finely ground coffee is added to the basket, hot water is then poured, sprayed or dripped on to the coffee and the extract drips through the filter into a container below. Practically speaking, these days there are two different types of filters used in manual or automatic brewers.
The filter types are paper filters, a direct adaptation of standard filter papers used in chemistry laboratories, which can be folded to fit a cone or come in various pre moulded shapes; and "Gold" filters, fine metal or plastic meshes usually built into the cone itself. Manual brewers can be as simple as a plastic or metal cone which sits on top of a cup, or as complex as a 12 cup Chemex glass brewer looking as if it escaped from a nearby lab.
Electric filter machines usually consist of a tank with a heating element, a water distribution system, a cone to hold the filter and the coffee, a carafe or jug of some sort to receive the brew and a hotplate to keep it warm. They are big business kitchen appliances and there are a number of bells and whistles added to various machines, including timers, settable thermostats, milk steamers and internet connections. (Internet connections are pretty rare at present, but they DO exist, although not on home appliances.)
When it comes to the different filter types, paper or mesh, my personal preference is always for the mesh type. Paper filters preferentially retain the coffee oils which carry flavour and aroma, and for me this always means that the resulting coffee lacks something. The mesh filters do not hold back anything from the coffee extract, but may produce more sediment depending on how finely the coffee is ground.
A correct filter grind is finer than that for plunger, but not quite as fine as used for an espresso pot. The coffee to water proportions are critical, as is the temperature of the water used for brewing. Below are some guides to getting the best out of your filter brewer.
Manual Filters:
1) Use 10g of finely ground coffee per 180 ml cup.
2) If you're using a paper filter, wet it with a splash of hot water before adding the coffee. This will cut down on the absorption of coffee oils into the paper.
3) Smooth out the coffee so it sits in the lowest part of the filter.
4) Bring your hot water to the boil, then remove the heat immediately. Wait 30 seconds for the water to cool to 95° C, then pour a little onto the coffee to wet it thoroughly. Continue pouring your water into the cone, making sure that it does not overflow.
5) When all the coffee has dripped through into the jug, remove the filter and serve immediately.
Filter Machines:
In my experience the definition of a "cup" depends on who makes the machine, and even then varies between models. You need to check the ACTUAL brewing capacity before you begin, then proceed as for steps (1), (2) and (3) above. A wise buyer will also determine the temperature of the brewing water as it exits the water distribution system, as many cheaper models tend to brew below the optimum 95° C level, resulting in thin, underextracted brews.
Again, I would prefer a machine with a permanent filter to one that uses filter papers; you get better flavour and pay much less in the long term for your brewing pleasure. However, Melitta, the inventors of filter brewing, have recently released special ‘micropore’ filters which absorb less oils, so if you're stuck with papers you might want to try these.
One thing to be careful of with Filter machines is the hotplate. Leaving coffee on the hotplate for longer than 30 minutes will result in a typical stewed brew. Another caution is that very fresh coffee in some poorly designed machines will produce so much froth that it will spill over the filter basket when you try to brew at the full capacity. The only solution is to drop back to around 75% of the nominal "full" brew.
