Chemex coffee too weak? Here is what to change

If your Chemex coffee is weak, make these changes in this order: weigh your coffee and move to 1:15 (for 500 g of water, use about 33 g of coffee), then grind one step finer, then pour water at 94 to 96 °C (201 to 205 °F), then slow your pour so the total brew takes about four minutes. Change one thing per brew, taste, and stop when it tastes right. Most weak Chemex cups are fixed by the first two steps.

Why is a Chemex cup weak in the first place?

A Chemex uses a thick paper filter, and that filter holds back oils and fine particles. The result is a very clean cup, but a cup that can taste thin if the recipe is a little off. The usual causes, in the order we would check them, are too little coffee, a grind that is too coarse, water that is not hot enough, and a pour that is too fast.

Weak is different from sour. A weak cup tastes watery and flat, with not much of anything. A sour cup is sharp and thin at the back. They overlap, and the fixes are close, but if the cup is mostly sharp, our pour-over coffee too sour post is the better page. For the general version of this problem, see pour-over coffee too weak. This page is for the Chemex specifically.

What do you change first?

1. Weigh the coffee. Scoops and tablespoons drift by a few grams, and in a big brewer a few grams matter. Our default is 1:16, covered in the how much coffee per cup page, and for a weak cup go to 1:15.
2. Grind finer. One step at a time. A Chemex grind is commonly described as medium-coarse, like coarse sea salt. If your cup is weak, you are probably at the coarse end.
3. Raise the water temperature. Use water just off the boil, around 94 to 96 °C (201 to 205 °F). Preheat the Chemex by rinsing the filter with hot water first, and discard the rinse.
4. Bloom properly. Pour about twice the weight of the coffee in water, wait 30 to 45 seconds, and let the bed swell and release gas.
5. Slow the pour. Pour in small circles over about three to four minutes in total. If the water runs through in two minutes, the grind is too coarse or the pour is too fast.

How much coffee for a weak Chemex?

Here is how much to move the ratio by. The water amounts are in grams (1 oz of water is about 30 g). The coffee is rounded to the nearest gram, and level tablespoons are 5 g each.

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.

What if it is still weak after all that?

Check the coffee itself. Ground coffee goes flat faster than whole beans, so if the bag has been open for weeks, a weak cup may be a stale cup. We cover how long beans last in a post on this blog about whole bean freshness, and our whole bean vs ground coffee comparison explains why grinding at home helps. A blade grinder also makes uneven pieces, and the fine dust clogs the filter while the boulders under-extract. See burr vs blade grinder.

If you are comparing the Chemex with other cones, Chemex vs V60 covers how the two brewers differ.

Which of our coffees is the safest choice in a Chemex?

This part is our judgment and not a label fact. If you want a middle of the road cup while you dial in a Chemex, we would start with No. 1 Common Sense. The label says Medium roast, with cocoa, red apple and brown sugar. A cup like that is easy to read, so you can tell whether a change helped. If you prefer a brighter coffee, No. 9 Optimism (Medium-light, pear, floral, jasmine, strawberry) is also made for pour-over, but the label says it is bright and tea-like and that it flattens faster as it cools, so drink it hot.

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Weigh it, grind finer, pour hotter, and change one thing per brew.