Common mistakes when using a Chemex

If you own an iconic Chemex coffee machine, you will already know its history and how German Peter Schlumbohm designed it in 1941. This patent in the US would culminate in a prolific career as an inventor, the Chemex being a simple piece of work that united science and marketing in a magnificent product. From the first moment, coffee fanatics fell in love with it, and it has continued to do so to this day.

Although the Chemex coffee maker, thanks to its design, is a very easy-to-use manual drip coffee maker, there are always unexpected drawbacks. A brewing time that is too slow can be frustrating and ruin our longed-for coffee. If you want to brew about 600 grams of coffee, the brewing time should be 4 – 5 minutes.

With the Chemex coffee maker, you get a super light-bodied coffee, more like tea than coffee. It is a very delicate coffee, bright and rich in flavour. The thick paper filters have a very big influence, giving a characteristic flavour to the resulting coffee.

The resulting cup will be very clean, clear and with pronounced acidity, highlighting floral and other more delicate notes.

What is Chemex, and what is the coffee extraction process like?

One of the most important features of coffee preparation with a Chemex is the presence of the specific Chemex paper filters, which are thicker and less porous than the traditional ones used in other drip coffee machines. These filters will influence the taste and the water pours that will be made in several batches.

Coffee prepared with the Chemex coffee maker
Coffee prepared with the Chemex coffee maker

The step-by-step guide I will give below will be for a standard brew with 38 grams of coffee for 600 grams of water at 92 ºC:

  • Weigh the 38 grams of coffee beans.
  • Grind the coffee to a medium and even degree in a coffee grinder.
  • Place a Chemex filter in the coffee maker (with the 3-ply side towards the spout of the coffee maker) and pour in a little hot water to remove impurities and eliminate some of the papery taste.
  • Once the rinse water has been discarded, place the 38 grams of ground coffee in the base of the filter and level it by shaking the Chemex a little.
  • Place the brewer on the scales and turn on the timer.
  • Add 76 grams of water at 92 ºC for pre-infusion (blooming), leaving it to brew for 30 to 45 seconds.
  • Add water in concentric circles without touching the filter or standing still in the centre. Ideally, use a gooseneck kettle.
  • Stop when you have filled a good amount of water and wait for the level to drop a little before adding the second batch of water to complete the 600 grams.
  • If the grind was correct and you poured the water correctly, the draining should be finished within 4 to 5 minutes.

As you can see in this preparation process, which resembles a ritual or an haute cuisine recipe, there are three pours; one for the pre-infusion, one for the first drain and a third for the final extraction of the coffee.

How long should a Chemex take to make coffee?

As stated above, a very reliable brewing recipe is 38 grams of coffee per 600 grams of water, where you can get 6 cups of very rich and light coffee. Our 600 grams of water recipe should take between 4 and 5 minutes, depending on the grinding and pouring.

The time it takes to brew coffee with Chemex has a wide range because it is very susceptible to change according to personal taste. If you want more body, you will have to pour faster (or grind coarser); if you want more nuances, you will have to pour slower (or grind finer).

  • If you use less water, for example, 300 grams, the time should be between 3 and 4 minutes.
  • If you use more water, 800 grams, the time should be between 5 and 6 minutes.

But it still depends on your taste; once you have tasted the coffee, you should adjust the pour-over and grind to get the perfect taste.

Why does my Chemex take so long?

Once we have established “average” brewing times for the Chemex and discussed pouring times and grind settings, you should know if your Chemex is taking too long or if it was just an impression.

If your brewing time takes more than 5 minutes for a 600-gram quantity of water, there is something wrong with the process. And the most common factors are too fine a grind or too slow a pour, although in some cases, it could be the use of the wrong coffee.

Too fine a grind

If the grind of the coffee beans is too fine, this ground coffee could saturate the filter and prevent the water from passing through it easily. Remember to use a grinder rather than a blade grinder and adjust the degree of grinding until the brewing time is right.

Pouring too slowly

The pre-infusion pour-over is not recommended to be modified as this is where the water releases the gases and aromas of the coffee, and the water is prepared for extraction. However, the next two pours can be modified to increase the extraction speed.

The water falls to the bottom of the Chemex by gravity, so the more water in the upper cone, the more pressure will be exerted, and the faster the water will fall. Try to increase the speed of the pours and the amount of water in the first pour. This will speed up the process.

Using the wrong coffee

If you do not use natural roast coffees and opt for roasted or very dark roast coffees, the excess oils can saturate the filter and prevent the water from passing freely to the bottom of the coffee machine. Always try to use coffees with very light roasts.

Other mistakes to avoid when using the Chemex

After explaining the 3 reasons why coffee brews too slowly in your Chemex, I will explain other common mistakes that lead to bad-tasting coffee.

In reality, you just need to follow the process explained above, but to make it easier, I will indicate below the key points to pay attention to:

The water temperature should be 95 ºC.

As you saw above, I recommend a water temperature of 95 ºC because if you use a lower temperature, the coffee can become too acidic. On the other hand, if you use too high a temperature, you can over-extract the coffee and get a bitter cup.

Always rinse the paper filter with hot water.

Although Chemex filters have their own “flavour mark”, it is not good if this flavour is too pronounced in the cup. It is inevitable that the paper filter flavour will end up in our cup, but it is good to rinse it with hot water before brewing our coffee, so it is not too predominant.

Don’t forget to preheat the Chemex

Linked to the previous two points, it is very important to run hot water through the top of the Chemex (and the filter) before brewing coffee.

We want the extraction to take place a little below 95ºC but never below 90ºC, so the hotter the Chemex glass and filter, the better.

Follow my recipe to the letter, and you will get superior coffee from your Chemex.

Related: Bullet Proof: What it is and how it is made.