Flash Brew Iced Coffee

What is flash brew? 

Flash iced brew coffee is simple. Take the full amount of water you would use in a hot brew and split it in half, replace half of that water by weight with ice. Then, extract over the ice. This melts the ice and rapidly dilutes the coffee, without that dilution the brew would be a double concentrated cup. Sometimes referred to as Japanese-style iced coffee, this style of brewing allows you to brew a cup of cold coffee without having too much dilution. This brew method produces bright and distinct flavor notes.  

What do I need? 

• Kalita / Flat-bottomed pour-over brewer
• Decanter 
• Filters
• Grinder 
• Kettle  
• Timer
• Scale
• Coffee
• Water
• Ice
• Particle Size Distribution Tool (optional)
• Glass (for drinking)

Recipe Breakdown

Let’s get into the recipe. Our brew is going to consist of three total pours, pretty manageable right? We’re looking to hit our goal weights in water at specific time intervals with a simple spiral pattern in and out. For our flash brew recipe we’re using a 1:15 – 15.5 ratio, this is the traditional strength level most of us would expect for an iced black coffee. 

Dose: 24.5g coffee

Grind: 560 um / 5 EK

Water: 185g hot water / 185g ice

Temp: 195°F 

Brew time: 2:25 min. 

Time marks:

• 0:00 – 40g of water to bloom, gentle flow touching all of the coffee. 
• 0:30 – 85g break pour, spiral in and out. 
• 1:10 – 60g last pour, spiral in and out.

Step 1

Fill your kettle with water and either let it come to a full boil, then let it cool for 25 – 35 seconds, or set your variable temperature kettle to 195°F. 

Step 2

Set up your brewing device and decanter with your filter in place. Pour hot water into the brewer until it’s almost filled to the top and allow all that water to drip through. This is going to ensure we rinse out any paper flavors in the filter and pre-heats the brewer which maintains our water temperature throughout the brew process. You can hold your hand on the brewer as you rinse your filter to feel for when the device is hot. Be sure to dump that rinse water out once it’s drained.

Step 3

Set an empty container on your scale and dose your coffee to grind – remember we’re using 18.5 grams for a 1:15 coffee to water ratio.

Step 4

Adjust your grinder to ensure the setting is correct. We’re grinding around 5 on our EK-43 grinder, this would be a 19 on a Comandante hand-grinder, or around 10 on a Baratza Encore. Turn your grinder on and add your beans to your hopper and allow those beans to grind all the way through.

Step 5

Another reminder here to dump our rinse water. Tare your scale and add 185g of ice cubes inside your decanter, your hot coffee will brew directly over this ice. Again, we’re dosing half of our total amount of water used in the recipe in ice. 

Step 6

Place your brewer on the scale and dose your coffee. Shake your coffee gently to level out your bed for an even extraction. Tare or zero out your scale again and get your timer ready to start brewing. 

Step 7

For our first pour we’re going to start the timer and begin the bloom. Blooming initiates the release of carbon dioxide in the coffee, which helps extract those delicious flavors available in our roast. A good amount of water to use for the bloom is double our dose (amount of coffee), poured with a light flow rate. We want to very delicately touch all of our grounds with the water until we hit our weight. Allow the coffee to degas and drip through for 30 seconds.

Step 8

Our second pulse (or introduction of water) is going to be 85g of water, our largest pour. This pour will begin right after our 30 second mark or bloom – it’s a roughly 6 circle patterned pour, spiraling in and out from the middle of our brew device bed with our last circles rinsing down the coffee on our filter wall. Keep in mind we’re using a bit of a heavier flow here, not a large stream of water but somewhere between this and our light bloom flow.

Step 9

Lastly, we finish up our brew with a 60g pulse of water. This pour is roughly 3-4 circles, spiraling out from the middle, with our last circle rinsing the edge of our filter. We should expect this coffee to drain around 2 minutes and 30 seconds – every coffee is different so you may have a quicker or longer brew time.

Step 10

Give your brew a swirl and let your ice melt some more along with the coffee. Make sure you have your glass ready with fresh ice, this is optional of course if you don’t want your iced coffee to be further diluted. Serve up your drink and give it a taste, you should expect a crisp, bright and refreshing experience out of the brew. 

Process

For this recipe, we used the Kalita because of its flat bed that ensures we touch all of our coffee during our brew. This creates a balanced flavor experience and a uniform extraction. In order to find the right grind size on our commercial grinder, we used Lighttells CM200. This device analyzes the size of the grinds by distribution.

Using our Mahlkonig EK-43 coffee grinder and a Kruve coffee sifter that separates large, medium, and find grind particles, we were able to dial-in the grind size and measure with the CM-200 to get a grind size of around 560 microns. This grind would allow for extraction within the ideal time frame. 

How we used the CM-200 to dial in the grind

On our EK grinder, we started with a setting of 5.25  and collected some data using the Kruve sifter and the Lighttells tool. For the first round, a max percentage of 21% in the 600-850 micron particle size range (or an average of 682um) with coffee that was sifted through the Kruve to get rid of any boulders and fines. While the uniformity was good, the grind was still a little too large for this brew method.

The second time was closer to what we wanted. We adjusted the EK-43 to a grind size of 5 and took another reading: 20% in the 425-600 particle size range averaging a grind size of 546 microns (um). For a flash brew, we’d ideally like to use a finer grind size like this since we have less water to pass through the coffee. This was a great place to stop and start brewing to taste while continuing to adjust the grind to taste.

Wrap Up

Flash brew is both a quick and an easy beverage to make for hot summer days – depending on the coffee you’re using you can enjoy a bright, delicate and fruity iced coffee or a classic dark, chocolate and nutty iced brew.