Flash Brew Chemex 800 g

Name: Flash Brew Chemex 800 g
Total time: 5 min
Yield: 800 g
Ingredients: 55 g coffee; 480 g water at 205F; 360 g ice

by Matt KennardUpdated October 1, 2026

Hot-brewed straight onto ice, so it's cold without being watered down.

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The ice counts as part of the brew water, so only 480g goes through the bed.

205F beat 203F: the shorter brew loses more heat per gram.

The long drawdown at 3.0 extracts past the bright zone into sweetness: roast forward, no acidity, some sweetness.

Keeps about 24 hours sealed in the fridge (the Chemex glass lid works).

Brew process

Rinse 360 g of ice

Rinse the paper and pour the water away, then weigh 360 g of crescent ice straight into the carafe. The ice is part of the recipe, not a garnish: the brew lands on it and chills in seconds, which is what keeps the aromatics that a fridge would lose.
Bloom 0:00 · 65 g total

Start the timer and pour 65 g over the whole bed. Then leave it — the bloom matters more here, because there is less water in total to do the extracting.
Pour 0:45 · 180 g total

Add 115 g in slow circles, off the paper.
Pour 1:40 · 330 g total

Add 150 g the same way.
Pour 2:30–2:45 · 480 g total

Add the last 150 g. The total is 480 g of water rather than 800 because the ice below is the rest of it.
Drawdown 5:00 · the bed dry, the ice mostly gone

Target: through by 5:00. Swirl the carafe to finish melting what ice is left, and serve it straight away over fresh ice if you want it colder.

These numbers were written for a Medium-dark roast. That is what the temperature and the time below assume — it is a setting, not a fact.

Dogspeed Flat Track Coffee Medium-dark · Latin America, varied seasonally — typically Colombia Supremo, Guatemala (Huehuetenango or Marilandia) and Brazil (Vila Boa natural) The one I use
Espresso Blue Bottle Coffee Dark · Organic blend, Latin America and Central Africa
Lucem Merit Coffee Medium · Blend, Honduras and Brazil; components shift, and it has also been listed as Peru and Colombia
Power Button Superthing Coffee Medium-dark · Blend, 50% washed Guatemala and 50% washed Ethiopia
Andino Leal Merit Coffee Medium · Huila, Colombia, from a committed group of small-scale producers
La Sagrada Praxis Coffee Roasters Medium-dark · Latin America, rotating seasonally through direct-trade lots (Mexico, Costa Rica and Guatemala among them)

If your bag is lighter or darker than that

55 g to 840 g is about 1:15. Everything below is relative to this recipe's own numbers.

Temperature: Go hotter. A lighter roast is denser and gives up less at the same temperature — take it to the top of the range, or just off the boil.
Time: Give it longer. Another fifteen to thirty seconds of contact, whether that is a slower pour or a longer steep.
Grind: Grind finer, one step. Light roasts under-extract before they over-extract, and sour is the failure you will meet first.
Dose: Leave the dose alone at first. If it is still thin after the other three, add a gram or two.

Temperature: Go cooler. A dark roast is brittle and gives up everything it has immediately — back off five degrees or let the kettle stand a minute.
Time: Cut it short. Stop the brew at the first sign of it slowing down; the last of the drawdown is where the ash comes from.
Grind: Grind coarser, one step. Bitter and hollow is the failure you will meet first, and coarser is the fix.
Dose: You can use slightly less and lose nothing. A dark roast tastes stronger than it is.

Temperature: The temperature on this recipe is written for exactly this roast. Start there.
Time: The time is the time. Change it only after you have tasted it once as written.
Grind: Grind is still the one thing worth moving. Everything else in the recipe is fixed so that it can be.
Dose: The dose below is what these numbers were dialed at.

More on what the words mean: light, medium and dark roasts.

Precision when it matters: why I love coffee — My love of coffee is the same thing as my love of Japanese cars: engineering that doesn't perform itself, and precision nobody else will notice.
Welcome to my kitchen — Why I cook, why I write it down, and what you'll find here.

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