Japanese Iced Coffee (Flash Brew)

Before you start

Japanese iced coffee, often called flash brew, is pour-over made with part of the brewing water replaced by ice sitting in the carafe. Hot coffee drips onto the ice, chills in seconds and melts it to the right strength. Because the coffee is extracted hot, it keeps the fruity, floral aromatics that cold brew never develops, and because it is chilled instantly, it tastes cleaner than coffee that cooled slowly.

The key decision is the split between hot water and ice. Here about 60 percent of the total water goes through the coffee hot and 40 percent waits in the carafe as ice. Less hot water means each gram of coffee sees less water, so grind finer than you would for hot pour-over to keep extraction on track. Light and medium roasts from Ethiopia or Kenya are especially good this way.

Ingredients

• 25 g (about 4 tbsp whole beans) light or medium roast coffee — ground medium-fine, slightly finer than for hot pour-over
• 225 g (225 ml) water, heated to 93 to 96°C (200 to 205°F) — plus extra for rinsing the filter
• 150 g (about 1 cup) ice cubes — in the carafe for brewing
• 1 cup (about 150 g) fresh ice cubes — for serving

Method

1. Heat the water to 93 to 96°C (200 to 205°F). Without a thermometer, let boiling water rest for about 30 seconds.
2. Weigh 150 g of ice into the carafe. Set the dripper on top, insert the filter and rinse it with hot water. Pour the rinse water out of the dripper side only, not onto the ice; if any reaches the ice, reweigh.
3. Grind the coffee medium-fine and add it to the filter. Shake it level and set the scale to zero with the whole setup on it.
4. Start the timer and pour about 50 g of water evenly over the grounds to wet them all. Let them bloom for 30 to 45 seconds while gas escapes.
5. Continue pouring in slow spirals, keeping the water level steady, until the scale reads 225 g of water at about 1:45. Avoid pouring straight down the filter walls.
6. Let it drain completely. The full drawdown should finish between 2:45 and 3:30. Much faster means grind finer next time; much slower means grind coarser.
7. Swirl the carafe until the remaining ice has almost melted and the coffee is cold. Pour over fresh ice in a glass and drink right away.

Tips for success

• Total water is 375 g for 25 g of coffee, a 1:15 ratio, the same strength as good hot coffee. The ice is not dilution added afterward; it is part of the recipe.
• Weigh everything. Eyeballing the ice is the most common reason flash brew tastes weak or sour.
• Use clear, fresh ice that does not smell of the freezer. Ice picks up odors and becomes part of the coffee.

Substitutions

Pour-over dripper

A drip machine works: put the ice in the carafe, reduce the machine's water by the weight of the ice, and grind a little finer. A Chemex works too with a slightly coarser grind.

Light roast coffee

Medium-dark roasts make a rounder, chocolatey flash brew. Very dark roasts can taste ashy when chilled this quickly.

Plain ice

Coffee ice cubes in the serving glass keep the drink from watering down as it sits.

Variations

Flash brew tonic

Pour 120 ml of the chilled coffee over ice and top with 120 ml tonic water.

Batch for two

Double everything in a larger dripper, and expect the drawdown to take about 4 minutes.

Troubleshooting

It tastes sour and thin

Under-extraction from a coarse grind or water that was too cool. Grind finer and check the water temperature; the reduced water volume makes this method sensitive to both.

It tastes bitter and dry

The grind was too fine or the drawdown ran too long. Grind slightly coarser and aim to finish by about 3:30.

It is not cold enough

Not enough ice was in the carafe, or it melted during the rinse. Weigh the ice after rinsing and serve over plenty of fresh ice.

Storage

Flash brew is at its best within 30 minutes. It can be kept covered in the fridge for a day, but its aroma fades quickly and it starts to taste flat. Store beans sealed away from light and grind just before brewing.

Safety notes

A 25 g dose makes a full-strength coffee with a typical amount of caffeine for a large mug. The FDA cites 400 mg a day as an amount not generally associated with negative effects for most healthy adults.