If your Chemex coffee is bitter, change these in order: grind one step coarser, then drop the water temperature to about 93 °C (200 °F), then end the brew by about four minutes, then move the ratio from 1:16 to 1:17 (for 500 g of water, use about 29 g of coffee instead of 31 g). Change one thing per brew and taste after each. Most bitter Chemex cups are fixed by the first two steps.
Why is a Chemex cup bitter?
Bitter usually means the water pulled out too much, and too much of the wrong things. The common causes are a grind that is too fine, water that is too hot, a brew that runs too long, or too much coffee for the water. The Chemex adds one more cause of its own. Its paper filter is thick, so a fine grind can clog it, the water slows down, and the coffee sits in contact for far longer than you meant. A slow drain is the first clue.
Bitter is not the same as sour or weak. A bitter cup is harsh and drying, and the taste lingers. If your cup is thin and watery, read Chemex coffee too weak instead. If it is sharp and thin, the same fixes in reverse apply, and pour-over coffee too sour covers it. For the general pour-over version of this problem, see pour-over coffee too bitter. This page is about the Chemex.
What do you change first?
- Grind coarser. One step at a time. A Chemex grind is commonly described as medium-coarse, like coarse sea salt. If the water drains slowly or the bed looks muddy, you are too fine.
- Lower the water temperature. Go from just off the boil to about 93 °C (200 °F). Let the kettle rest for 30 seconds after it clicks off. Rinse the filter with hot water first and discard the rinse.
- Finish the brew sooner. Aim to be done by about four minutes total. If it takes six, the grind is too fine or you are pouring too slowly.
- Pour less aggressively. Heavy stirring and hard pouring push fines into the filter. Pour gently in small circles and leave the bed alone.
- Use a little less coffee. If the first four steps are done and the cup is still harsh, go to 1:17.
How much should the ratio change?
Here are the amounts of coffee in grams at three ratios, for common amounts of water. Coffee is rounded to the nearest gram, and 1 oz of water is about 30 g. Level tablespoons are 5 g each.
| Water | 1:16, default | 1:17, softer | 1:18, softest |
|---|---|---|---|
| 300 g (10 oz) | 19 g | 18 g | 17 g |
| 500 g (17 oz) | 31 g | 29 g | 28 g |
| 700 g (24 oz) | 44 g | 41 g | 39 g |
Chemex sizes are commonly sold as 3 cup, 6 cup, 8 cup and 10 cup models, and those cup counts are small, so check your own pot and use the water you plan to pour. For exact numbers per pot, see how much coffee for a 6 cup Chemex and how much coffee for a 3 cup Chemex. The How much coffee per cup page explains why we start at 1:16, and the pour-over ratio cheat sheet adds timing.
Could the grinder be the problem?
Often, yes. A blade grinder makes a mix of boulders and dust. The dust over-extracts and tastes bitter while the boulders under-extract and taste sour, so you get both in one cup, and no amount of recipe changes will fix it. A burr grinder gives you pieces of one size. We compare them in burr vs blade grinder. Also check how long the bag has been open. Stale coffee can taste flat and dry, which people often describe as bitter.
Which of our coffees is the most forgiving in a Chemex?
This part is our judgment and not a label fact. If you are fighting bitterness, start with a coffee that is hard to push over the edge. No. 6 Hegemony is the one. The roaster describes low acidity and heavy body, and says it is very hard to ruin. The label says brew it as drip, and the same traits help a pour-over, where you are changing grind and time and want a coffee that does not punish a small slip. A second choice is No. 8 Consent, which the label calls clean and sweet, with nothing in it to push back against.
Our pick
No. 6 Hegemony
Parana and Sao Paulo, Brazil · 750 to 1,050 m · Pulped natural, sun dried · Catuai, Mundo Novo · Medium
Cocoa and smooth on the label, with low acidity and heavy body, so a small mistake with grind or time does not wreck the cup.
One note on coffees we would avoid while you troubleshoot. The roaster says No. 4 Conjuncture is acidic on purpose, and No. 9 Optimism flattens fast as it cools. Both are good coffees, but they make it harder to tell bitter from bright while you are still dialing in the brewer.
How many Chemex pots does a 12 oz bag make?
A bag is about 340 g. At 31 g per 500 g pot, that is about 11 pots. Every one of our coffees is $28 for 12 oz, whole bean or ground, with free shipping in the US, so the cost per pot is the same whichever bag you pick. Browse all ten coffees, or put one on a subscription, 11% off, skip or cancel in one click, so you always have fresh beans to practice with.
Grind coarser first, and give the next pot four minutes.
Questions people ask
Why is my Chemex coffee bitter?
Usually the grind is too fine, the water is too hot, or the brew runs too long. The thick Chemex filter clogs easily with a fine grind, which slows the drain and over-extracts the coffee.
What temperature water for a Chemex that tastes bitter?
Try about 93 °C (200 °F), which is just under a rolling boil. Let the kettle rest 30 seconds after it switches off, then pour.
How long should a Chemex brew take?
About four minutes in total, including the bloom. If yours takes six, grind coarser. If it finishes in two, grind finer.
Free printable
Keep the ratio chart on your fridge
One page with grams, level tablespoons and scoops for every cup size and for coffee makers from 2 to 14 cups. Leave your email and the download link appears right here.