How to Make Flash Brew Coffee at Home
Flash brew, also known as Japanese-style iced coffee, brews hot coffee directly over ice. The rapid chill locks in acidity and aromatics that long cold brew steeps tend to lose, and the whole process takes minutes rather than hours.
What Is Flash Brew Coffee?
Flash brew is a quick, hot-to-cold brewing method that extracts coffee with hot water, then chills it immediately over ice. This locks in the coffee's bright, complex flavours while limiting bitterness and oxidation.
Unlike cold brew, which steeps in cold water for 12–24 hours, flash brew is ready in minutes and produces a clean, crisp cup with a full flavour profile.
Why Use Permanent Ice Cubes?
Our take on flash brewing uses permanent ice cubes, typically made from stainless steel or food-safe plastic. These reusable cubes chill the coffee without diluting it, so the flavour stays consistent from the first sip to the last.
Flash Brew Recipe by Katie, Ozone's Customer Support Manager
We asked Katie Glover, our Customer Support Manager, to share her go-to flash brew method for making iced coffee at home. Here's her step-by-step guide.
Ingredients & Equipment
- 21g coffee — coarse filter grind (Katie uses 10 clicks on a Porlex grinder)
- 300g water at 92°C
- Reusable ice cubes (plastic or stainless steel)
- Large Clever Dripper
- 2 carafes — a glass server like this Kalita works well
- Paper filter
Brewing Instructions
- Prep your brewer. Place a paper filter in the Clever Dripper and rinse with hot water. Discard the rinse water.
- Add ice. Divide your reusable ice cubes between two carafes: 200g in the first, 150g in the second.
- Brew. Fill the Clever Dripper with 300g of hot water. Add the ground coffee and stir to ensure all grounds are saturated.
- Steep. Let the coffee steep. Stir again at 1:30.
- Drain. At 3:00, place the Clever Dripper on the first carafe to drain.
- Chill. Let the coffee sit in the first carafe for 3 minutes, stirring occasionally to cool it further.
- Final chill. Pour the coffee into the second carafe for an extra chill. Look for condensation on the glass as a sign it's ready.
Frequently Asked Questions
What's the difference between flash brew and cold brew?
Flash brew uses hot water and is brewed directly over ice, preserving acidity and aroma. Cold brew is steeped in cold water for 12–24 hours, producing a smoother, less acidic cup with a different flavour profile.
Can I use regular ice instead of permanent ice cubes?
Yes, but regular ice will dilute the coffee as it melts. If you use regular ice, we recommend brewing with a slightly higher coffee-to-water ratio to compensate.
What type of coffee works best for flash brew?
Light to medium roasts tend to work well, particularly those with fruity or floral notes. These characteristics come through clearly with the flash brew method.
Do I need a Clever Dripper?
No. You can use other brewers including a Kalita Wave, V60, Chemex, or AeroPress. The key is controlling brew time and chilling the coffee quickly.
Is flash brew stronger than cold brew?
Flash brew tends to taste brighter and more complex. Cold brew can have a higher caffeine content depending on the ratio and steep time, but this varies by recipe.
