What is Chemex coffee and how do you make it?
Coffee aficionados have been purring over the Chemex drip-filter coffee maker. For the uninitiated, the Chemex is a borosilicate glass pour-over flask, invented in 1943 by the chemist and inventor Dr. Peter Schlumbohm. The classic Chemex is simply an hourglass shaped carafe.
It is gripped from a wooden neck collar that held in place by a leather tie. The design is timeless, elegant and was inspired by the Bauhaus movement. Although the Chemex has entered the mainstream fairly recently it has enjoyed a cult following for many years. In the 1957 novel ‘From Russia With Love’ James Bond cites it as his preferred method of brewing coffee.
But what’s behind the machines long-lived popularity? How do you brew using a Chemex? And is it worth investing in a Chemex?
The Chemex Science
Chemex coffee is prized for its smooth and thin mouthfeel, low acidity and low bitterness. The Chemex achieves this in two ways.
Firstly, the machines use patented Chemex-brand filter paper, which is around 30% thicker than other paper on the market. The added thickness means prevents oils and sediment from the coffee grounds getting into the final cup, keeping things smooth and mellow.
Secondly, each flasks upper conical section that holds the filter paper is the perfect shape to facilitate a process known to baristas as ‘coffee-bloom’ or ‘degassing’. Sounds fancy, but it is in fact a very simple concept.
When making a flask of coffee, a small amount of water is poured on the grounds to wet them at at the start of the brewing process. This water allows carbon dioxide gas trapped inside the bean to be released. This is beneficial in two ways:
One: Lower levels of CO2 dissolved in the final cup makes it less acidic.
Two: Letting the CO2 escape at the start of the process means the water has more time to work directly on the grounds during brewing, which helps deliver more flavour into the finished product.
The Chemex Kit and Caboodle
The classic chemex comes in 3, 6, 8 and 10 cup-sized versions, which retail for between £40 and £50.
Chemex determine a cup as 142 millilitres of black gold, which is on the small side. The average mug is around 350 millilitres.
The smallest iteration of the Chemex will brew up around a pint, the largest near one and a half litres.
One of the drawbacks to the Chemex is that you have to order the papers yourself too. These don’t come cheap, with packs of 100 retailing for around the £12 bracket.
There’s also a whole other level of coffee geekery at play with the filter papers. Both bleached and non bleached varieties are available. While there is no difference in terms of taste and function, non-bleached paper is a greener bet as its production is much more eco-friendly.
Papers come pre-folded, although you can also get ones that you need to fold yourself.
Plenty of fanatics extol the virtue of the DIY approach, but the main difference seems to be that brewing takes on an extra step, which is also a fun origami challenge. The filter papers can also have squared or rounded edges, depending on your preference.Some people prefer the square ones as they are slightly easier to remove from the carafe when brewing has finished.
here are also metallic filter baskets on the market that will fit the machine, but these are not official or endorsed by the company. Given the paper itself is central to the brewing process, we’re not sure why anyone would bother – but if that’s your bag we are not going to yuck your yum.
There are a whole bunch of official accessories you can buy for the Chemex too.
There are chemex lids which allow you to cover up brewed coffee and stop it from oxidising and help keep your brew warm.
Once brewed the Chemex can be kept warm by placing the jar over a low gas flame or putting it on a hot plate. However if you have an electric hob, you will need to invest in a wire rack to sit the unit on unless you want it to shatter.
Alternatively, you could just wrap a tea towel around the freshly brewed carafe to keep it warm like we all used to do in the old days.
The Chemex is non-reactive and dishwasher safe and can be cleaned by hand. Remove the wooden collar before washing in both cases. Clean it out with hot soapy water and rinse well.
Given the awkward shape of the flask manual cleaning can be a faff, but there are cleaning brushes available that help you get the job done.
How to make the perfect Chemex in 7 Steps
Obviously the ‘perfect’ Chemex coffee depends on individual tastes. These ground rules will help you nail a lovely cup every time, but there is no ‘magic recipe’ for great coffee.
Feel free to play around with grind size, coffee and water ratios, but let the technique below guide you.
Get your filter paper into the spout of the machine. As you open up the paper you will notice that one side of the cone has multiple layers on it. This side is more robust and goes against the spout.
If you put the single ply layer against the spout it will collapse into the spout during brewing and disrupt airflow in the machine.
Pre-wet your filter with some boiling or near-boiling water. Pour water through the paper and let it gather in the bottom of the flask. This will remove any residual paper flavours from the filter and pre-heat the glass so it doesn’t leech all the heat from the coffee later.
Once everything is nice and warm, toss away the water.
Add around 7 grams of coffee per person. The general consensus is that this should be in a medium-course ground, with grains the size of Kosher salt.
Grinding your coffee seconds before you put it in the filter is going to deliver a cup much better than if using pre-ground.
Heat some filtered water to between 92-94 degrees, the magic temperature for brewing coffee. Hotter water will burn the beans.
Tap water and excessively hard water will obviously impact the final taste of the coffee too as they contain chemicals which interfere with the brewing process!
Pre-wet the coffee grounds. Pour enough hot water over the grinds to wet them all. Stir it up if you need to to ensure there are no dry clumps hiding in there. Once your coffee is nice and wet leave it for 45 seconds. The grounds will expand, bubble and bloom. Lovely.
Pour over the water – but get the pour right!
Pour a slow thin stream of water over the coffee using a wiggling/spiralling motion.
This generates a bit of turbulence that helps extract all that coffee goodness from all the grounds. Take about a minute and a half to slowly pour over the of the water you are using in a nice trickle.
Stop pouring and let the water level drop if it rises too close to the rim, and then carry on. Hardcore Chemex fans use thin-spouted gooseneck kettles to ensure they can pour it out nice and slow.
By the time you finish adding the water the top of the brewer will be pretty full. Wait for all the water to filter through. This will probably take another 30-45 seconds.
Remove the filter paper from the top of the flask and discard. Pour the coffee into glasses and enjoy.