Flash Brew Coffee with Permanent Ice Cubes: A Modern Guide to Japanese-Style Iced Coffee

Looking for a fast, flavourful way to enjoy cold specialty coffee without waiting hours for a cold brew? Flash brewed coffee—also known as Japanese-style iced coffee—is the perfect solution. This method brews hot coffee directly over ice, preserving the vibrant acidity and delicate aromatics that are often lost in traditional cold brew.

What Is Flash Brew Coffee?

Flash brew is a quick, hot-to-cold brewing method that uses hot water to extract coffee, then rapidly chills it over ice. This technique locks in the coffee’s bright, complex flavours while preventing bitterness and oxidation.

Unlike cold brew, which can take 12–24 hours to steep, flash brew is ready in minutes and delivers a refreshing, crisp cup with a full flavour profile.

Why Use Permanent Ice Cubes?

Our modern twist on flash brewing involves permanent ice cubes—typically made from stainless steel or food-safe plastic. These reusable cubes chill the coffee without diluting it, ensuring a bold, consistent taste from the first sip to the last.

Flash Brew Coffee Recipe by Katie, Ozone’s Customer Support Manager

A woman with brown hair wearing dungarees and a striped t-shirt against an orange backdrop.

We asked Katie Glover, our Customer Support Manager, to share her go-to flash brew method for making delicious 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, widely available online)
Large Clever Dripper
2 carafes
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
Split 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 for that perfect icy finish ❄️

Frequently Asked Questions (FAQs)

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, resulting in a smoother, less acidic cup.
Can I use regular ice instead of permanent ice cubes?
Yes, but regular ice will dilute the coffee as it melts. Permanent ice cubes chill the coffee without affecting its strength or flavour. If you would like to use regular ice, we recommend brewing with additional coffee to balance the overall brewing ratio.
What type of coffee beans are best for flash brew?
Light to medium roasts tend to work best, especially those with fruity or floral notes. These flavours shine through with the flash brew method.
Do I need a Clever Dripper to make flash brew?
Not necessarily. You can use other brewers like a Kalita Wave, V60, Chemex, or AeroPress. The key is controlling the brew time and chilling the coffee quickly.
Is flash brew stronger than cold brew?
Flash brew often tastes brighter and more complex, but cold brew can have a higher caffeine content depending on the ratio and steep time.

Final Thoughts

Flash brewed coffee is a game-changer for iced coffee lovers. With the added benefit of permanent ice cubes, you get all the chill with none of the dilution. Whether you're brewing at home or in a café, this method delivers a clean, vibrant cup every time.