Filter Coffee Decoction: How Strong, How Long, How to Store It

Get the decoction right and a so-so pour still tastes good. Get it wrong and no amount of milk or sugar saves it. Here's how strong it should be, how long it should take, and how to store what's left.

In short: use about 15 g of coffee and 60 ml of water per cup, roughly 1:4. The drip should take 10 to 15 minutes. Good decoction is near-black and slightly syrupy. It keeps two days in the fridge, so brew once and build fresh cups with hot milk.

What coffee decoction is

Decoction is very strong coffee made by slow gravity drip. Water sits on fine grounds in the top of a steel filter and seeps through on its own, over 10 to 20 minutes.

It isn't espresso, because there's no pressure. It isn't cold brew concentrate either, because it's brewed hot. It's one of the few brewing methods designed from the start to be mixed with hot milk.

How strong should coffee decoction be?

• Coffee: two heaped tablespoons, about 15 g, per cup.
• Water: about 60 ml per cup.
• Ratio: roughly 1:4, coffee to water.

A pour-over runs about 1:16 and an espresso about 1:2, so decoction sits much closer to espresso. That's why it survives being diluted with three or four times its volume of milk.

Want it stronger? Add coffee, don't cut water. Below about 50 ml of water per cup, part of the bed never gets wet.

How it should look: hold the lower chamber to the light. Good decoction is opaque, near-black and coats the steel as you tilt it. If light comes through, it's weak and the coffee will taste like sweet milk.

How long it should take

Drip time	What it means	What to change
Under 6 min	Water is rushing through	Grind finer, level the bed
6 to 10 min	A bit fast, often thin	A click or two finer
10 to 15 min	Right where you want it	Nothing
15 to 20 min	Slow, sometimes harsh	A click coarser if it's bitter
Over 20 min or stalled	The bed has packed down	Grind coarser, stop pressing the disc

Time tells you about the grind. You're after fine rava, sandy with a little powder. There's more in the right grind for a South Indian filter.

Four things that decide it

• Water temperature. Just off the boil, 90 to 96°C. Take the kettle off, count to twenty, then pour. This alone fixes bitter decoction about a third of the time.
• The bloom. Wet the grounds with about 30 ml and wait 30 seconds before filling up. Fresh coffee puffs as gas escapes. If nothing puffs, the coffee isn't fresh: see does coffee go bad?
• The pressing disc. It levels the bed. It isn't a tamper. A gentle quarter-turn, nothing more, or the flow slows to a crawl and the coffee turns bitter.
• The lid. Keep it on. Every time you lift it to check, the brew cools and slows.

How to store decoction

Decoction keeps. Milk coffee doesn't. Brew a batch, refrigerate it, and make each cup fresh. It turns a 15-minute morning into a 90-second one.

• Fridge, covered: two days easily, three at a push. After that it goes flat and a little sour.
• Room temperature: a few hours at most.
• Freezer: pour it into an ice tray. The cubes keep for weeks, and they're the right ice for cold coffee at home.

Reheating: warm the milk, not the decoction. Boiling decoction again kills the aroma and pushes it bitter. Cold decoction poured into properly hot milk lands at drinking temperature anyway.

How much to make: a 200 ml filter with three or four tablespoons gives about two days of coffee for one person. Don't make more than that.

Building the cup

1. Heat the milk until it steams. Don't boil it hard.
2. Stir the sugar into the milk, not the finished coffee.
3. Pour 30 ml of decoction into the tumbler and 120 ml of hot milk on top.
4. Pull it between tumbler and dabara, from a height, six or seven times.

Too weak? Go to 40 ml of decoction before you brew it stronger. Most weak-coffee complaints are the milk ratio.

Which coffee to brew

Velvet Mocha is built for this: dark chocolate and a gentle sweetness that holds through milk, sold in the South Indian Filter grind. Toasted Almond and Cookie Bandit make excellent decoction too and are sweet enough that most people cut the sugar. Buy those two as whole beans and grind them fine rava at home.

The full method is in how to make filter coffee at home. If your decoction is coming out harsh, try these five fixes for bitter filter coffee.