Filtering coffee - the techniques

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Filter coffee, often made with stale beans and left to stew for hours, quickly fell out of favour with the arrival of the espresso machine. But interest in single origin artisan coffees and local roasters has led to a revival in this traditional coffee brewing method. Coffee filtering is good at bringing out the subtle qualities of the beans and there are plenty of filter methods to choose from.


In "Filtering coffee - the principles" we look at the various processes and some of the science involved when you make filter coffee. This page looks at different filter methods, each of which creates a cup with a slightly different flavour profile.

No two people are looking for the same taste in their cup so although there are some basic ground rules when you start making filter coffee, in order to achieve your preferred flavour profile, you'll need to experiment with grind size, coffee to water ratio and brew time (bearing in mind that the order of flavour extraction from the bean, regardless of the method, is salt, acid, sweetness and finally bitterness). Because of the number of variables, it's worth making notes as you go.

As a starter, use 5 to 7g of coffee to every 100ml of water. Water should be between 88°C and 92°C. Colder and it won't make it into the grind to extract flavour, hotter and it will destroy flavour.

As well as your chosen filtering device, you will need a scale, grinder, kettle and thermometer. It's essential to keep all your tools clean and dry so as not to contaminate the coffee with unpleasant musty flavours.

Though there are numerous ways to make filter coffee, all methods are essentially based on one of four processes: pour over, pressure, immersion or a combination of these.

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Pour over


This method entails slowly pouring water over coffee grounds which are resting on a filter. Gravity draws water down through the coffee to produce a brew that is free of sediment. Because pour over is gentler than the espresso method (which applies up to ten bars of pressure), because it's a slower process, and because it uses more water, pour over produce a drink with a more complex, delicate flavour. It is particularly good at drawing out sweeter notes which need time to come through. Diluting an intensely flavoured espresso to make an Americano does not produce a drink that is anywhere near as complex as a pour over.

Pour over systems


There are several different pour over systems, some of which incorporate the dripper and the receptacle into one piece. To improve the flow of coffee through the filter, some drippers include grooves or ridges which can be spiral-shaped, straight or staggered. These grooves create little channels between the filter paper and the sides of the dripper to facilitate the movement of the coffee away from the filter paper so it can flow freely into the vessel below. This reduces the risk of over extraction as a result of the liquid lingering around the grounds.

Made by Japanese glassmaker Hario, the V60 is reasonably priced and simple to use, making it one of the most popular pour over systems. Taking its name from the 60° angle of its sides, it is a conical over-the-cup brewer with a wide aperture allowing for fast water movement. Filtration grooves on the inside of the dripper contribute to uniform extraction to give a bright balanced cup. For a more intense brew from the V60, use more coffee or grind finer to increase water resistance.

With its wooden collar, the Chemex, which was designed in the 1970s, is something of a design classic - it can be found on display in New York's Museum of Modern Art. It comes in several sizes and the dripper and decanter form one unit. It's usually used for making more than one cup. There is just one large filtration channel, so water moves through the coffee more slowly than in the V60. Because of the increased volume of water and the slow speed of the water, a larger grind is used to avoid over extraction. The Chemex is good for a nice sweet cup though some people can detect the flavour of the paper filter (even after a good washing) which is thicker and heavier than the thin light filter paper used in the V60.

The ribbed sides and three holes in the wide flat bottom of the over-the-cup Kalita Wave Dripper, as well as the curly waved edges of its paper filter are designed for good water flow and uniform extraction so this system is particularly well suited to beginners as it's not overly sensitive to the pour. These filters are more expensive than the V60 filters.

Providing complete control over infusion time, the Clever Brewer has a tap at the bottom of the cone, in effect allowing it to double as an immersion brewer. It comes with a lid and takes paper filters.

The weave of the deep cloth filter suspended from a metal ring in the Woodneck completely eliminates the risk of paper tastes and produces coffee with plenty of oils, thus giving greater mouthfeel. The best place to store the filter is in the freezer.

The syphon


Syphon brewing dates back to at least 1827 and today's vacuum pots are pretty much the same in design as the model that was perfected in 1841 by Madame Vassieux of Lyon. Syphon brewing makes for great live entertainment and requires some expertise. The brewing process maintains a more even water temperature than other methods, which for Tristan Stephenson in The Curious Guide to Coffee "tends to pull out more of the dark caramel and rich, nutty characteristics in the coffee."

Water is heated in a lower chamber, above which sits a second loosely attached chamber containing the coffee and a filter. When the water in the lower chamber reaches boiling point the operator seals the upper chamber. Steam in the lower chamber forces the water into the upper chamber. Once all the water has transferred to the upper chamber the heat source is removed, the pressure in the lower chamber drops. This lower pressure pulls the brew back down through the filter. To slow the downwards movement of the water, some systems incorporate a capped spout on the lower pot. When the cap is removed the pressure in the pot equalises with the outside air (pressurization) and the brew flows down into the lower pot under gravity alone.

AeroPress


Much loved by professional baristas, who will spend hours toying with the variables available to this method, the AeroPress is best described as a large, clear plastic syringe. It was invented in 2005 by professor Alan Adler, the president of Aerobie, is fairly cheap to buy, simple to operate, facilitates great control over the brew process and is an easy way of making a single cup at home.

It combines immersion and pressure brewing, can be used in two different ways and is a great device for playing around with grind size and timing to achieve different flavour profiles. Press the water through quickly, for instance, and you've got a lighter sweeter drink. Leave it to brew longer and the coffee will be more intense. As in the French press, the coffee is fully immersed and water is pressed through the coffee, but because this is an air tight unit it's pushed through at a much higher pressure - about two bars. This forces some of the coffee oils through the filter, giving a body rich drink. The paper filter (metal ones are available) gives a crystal clear brew that is free of fines.

The AeroPress can be used traditionally or inverted.

Traditional: place finely ground coffee on top of the filter paper in the bottom of the larger cylinder. Pour water over the coffee and stir for about ten seconds to get rid of any air trapped in the grounds (so no need to bloom). After about a minute insert the plunger, place over a cup and depress.

Inverted: It was baristas that started turning the AeroPress upside down to rest the device on the plunger, making it a little more like the French press. Coffee now sits on the bottom of the plunger instead of on the filter which is screwed to the top later. The device is then flipped over (which gives the brew a good agitation) to sit on the cup. Used this way up there is no air trapped in the system which makes pushing the plunger down easier.

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Moka pot

Moka Pot


The Moka pot, or stove top pot, was patented by Alfonso Bialetti in 1933, though it was actually invented in 1833 by an Englishman named Samuel Parks. Used properly it makes great coffee, used badly it makes terrible over extracted sooty coffee. Pots come in several sizes. The bigger the pot the longer the extraction time because of the amount of water heating that needs to take place, so if using a very large pot use a larger grind to avoid over extraction and make sure you have an adequate heat source.

Like the syphon, the Moka pot operates as a result of the physics of pressure. When water is heated in the sealed base section, pressure builds and hot water is forced up through a pipe into a bed of coffee in a middle chamber. It then moves up, now as coffee, into a top chamber. Some pots have a weighted valve that prevents the movement of water until enough pressure is achieved - this helps prevent over extracted coffee. Always fill the pot to capacity to ensure that water passing from the lower chamber is at working temperature for proper extraction.

When you are aware that coffee is starting to appear in the top chamber open the lid of the pot and adjust the rate of water flow (and hence the extraction rate) by adjusting or turning off the heat source.

If you are using the Moka pot at an altitude where water boils at above 92°C (pretty much everywhere except Everest) you can try and keep the brewing temperature down and thus minimise damage to the coffee by preheating the lower chamber and using pre boiled water. Keep the upper chamber separate and cold and when you seal it to the lower chamber you should already have slightly different pressures in the two chambers.

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French press

French press


The French press, also known as cafetière or plunge pot, is still one of the best ways of making coffee at home. Its great advantage is that it gives complete control over extraction time. It's good for a full bodied oil rich cup, though it can sacrifice the lightness and clarity of other methods. Patented in France in 1852 as an 'Infusion Coffee Maker', this method was only really perfected in the 1980s with the introduction of nylon filters. Grind size needs to be a little coarser than it would be for a Pour Over method and always use a pot size that will be filled so as to maintain a good brewing temperature.

Pre-heat the pot and bloom the coffee with about 15% of the water for 30 seconds, though as the coffee will be immersed and you will be stirring, blooming is not essential. Add the remaining water, stir and extract for about four minutes. To get rid of fines that will inevitably make their way through this filter, skim them off the top of the coffee before you depress the filter and allow the brew to rest before pouring. After pressing the plunger, decant or pour the coffee immediately to avoid over extraction.

Regional methods


As coffee is consumed globally it goes without saying that there are numerous regional methods for preparing a brew. Here are just a few:

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Turkish coffee pot

Full immersion in a The Coffee Pot, without a filtering step, is the oldest preparation method and is the one used in Turkey to this day. Water and coffee are simply mixed in the coffee pot, the spout of which is positioned midway up the pot, between the floating fines at the top and heavy grounds at the bottom. Despite this plenty of grinds find their way into the cup - it's an acquired taste and calls for a very fine grind.

In Colombia and other Andean countries, a very fine grind is added to a saucepan of pre-boiled water and after five minutes, once the grinds have settled, the brew is carefully poured and often sweetened with panela (unrefined whole cane sugar).

The Chorreador is a filtering system from Costa Rica in which hot water leaches through coffee grounds held in a cloth filter mounted on a wooden stand.

The south Indian coffee maker consists of two metal tins. One tin, the brewing chamber, with its pierced bottom, rests on top of the second tin - the tumbler. A coffee and chicory blend is tamped into the top chamber with a pierced metal disc which is left in place when the water is poured. Chicory retains water longer than coffee, thus holding the water against the coffee to produce a very strong brew, just a teaspoon or two of which is mixed with hot milk and sugar.

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Vietnamese coffee brewer

The Vietnamese Phin Brewer is similar to the Indian Brewer except that a saucer like filter is rested on a cup and the tamping filter can be screwed down in some models. A centimetre or so of condensed milk is placed in the cup before brewing commences.

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