Dirty Coffee
ダーティーコーヒーdaa-tee koh-hee
A small glass of ice-cold milk with a hot ristretto floating on top, its crema running down the inside of the glass in dark streaks. You drink it straight away, unstirred, so the first sip is all coffee and the last is cold sweet milk.
At a glance
- Ristretto : milk
- 1:4
- Active time
- 3 min
- Total time
- 4 min
- Makes
- 1 small glass
- Serve
- Immediately, unstirred
- Kit
- Espresso machine
Ingredients
Note: Whole milk only. Lower fat milk is thinner and the coffee sinks through it too quickly.
Method
-
Freeze the glass, chill the milk
Put a small heavy glass in the freezer for twenty minutes. Put the milk somewhere very cold for ten. The colder both are, the better the layer holds.
Freeze 20 minutes -
Milk into the glass
Pour the cold milk into the frosted glass, leaving about two centimetres at the top.
-
Pull the ristretto onto it
Put the glass under the portafilter and pull a double ristretto straight onto the milk, so it falls gently. About 25 ml in 20 seconds.
The hot, short shot is lighter than the ice-cold milk, so it floats. Its crema runs down the sides as it spreads. That is the dirt.
About 20 seconds -
Drink it now, unstirred
Serve it immediately and drink it within a minute or two without stirring. It is a short-lived drink by design.
Why this works
The layer depends on density, and density depends on temperature. Hot liquid is less dense than cold, and a 90°C ristretto is noticeably lighter than whole milk at 2 or 3°C. A ristretto is also short and concentrated, with a high proportion of crema, which is a foam of oils and gas and lighter still. Pulled gently onto very cold milk, it floats and spreads, and the crema slides down the inside of the glass in the streaks that give the drink its name.
Full-fat milk helps in two ways. It is slightly more viscous than skimmed, so the coffee sinks through it more slowly. And its fat carries flavour and sweetness at low temperatures, which is what the last sips depend on.
The drink is meant to be short-lived. Within a couple of minutes the coffee cools, its density rises, and it starts mixing into the milk. That is fine, but the point is the contrast: hot, bitter, concentrated coffee hitting the lips first, then the cold milk beneath. Stirring turns it into a small, lukewarm, unremarkable latte.
The idea is usually credited to Bear Pond Espresso in Tokyo's Shimokitazawa, whose owner served a drink called the Dirty: ristretto on cold milk. Around 2017 versions of it spread through cafés in China, where it is known as zāng zāng kāfēi, and in South Korea, and it became one of the most photographed coffees on social media in the region.
Variations
- Dirty matcha: ristretto over cold matcha milk, the green and dark layers together.
- Dirty with cream: replace 20 ml of the milk with single cream for a richer base.
- Dirty oat: barista oat milk, very cold. It layers well.
- Cold dirty: ristretto pulled into a frozen shot glass, then poured on, for a milder contrast.
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Questions
What is dirty coffee?
A hot ristretto poured onto very cold whole milk in a chilled glass, so the coffee floats on top and runs down the sides. It is drunk straight away without stirring.
Why does the coffee float on the milk?
Hot coffee is less dense than very cold milk, and a ristretto carries a lot of light crema. As long as the milk is very cold and the shot is poured gently, it stays on top.
What is the difference between dirty coffee and a latte?
A latte uses hot steamed milk mixed with espresso. Dirty coffee uses cold, unsteamed milk with a hot ristretto layered on top, and is drunk unmixed.
Where did dirty coffee come from?
It is usually credited to Bear Pond Espresso in Tokyo. It went viral in China and South Korea around 2017.