It’s getting to be the season for iced coffee in the northern hemisphere, and there are a dizzying array of methods to prepare it.
Last summer marked the year that “cold brew” coffee—a method that steeps coffee grounds for many hours with cold or room temperature water—went mainstream. Cold brew, which has a smoother, less bitter taste, represented a radical improvement in summer-appropriate coffee.
But iced coffee lovers, there is a better way.
It’s called flash-brewing (aka ice brewing), and is produced by pouring near-boiling water over coffee grounds, and then chilling it immediately. It preserves more delicious coffee flavor and takes only a minute or two to make at home. And when it’s prepared by coffeeshops using a method that infuses the coffee with nitrogen for storage and serving, it offers up the perfect summer drink: bright, crisp, and creamy, without having to add milk.
The chemistry of iced coffee
First, a bit of science: cold brew and ice brew taste very different because of the way they’re prepared.
Cold brew relies mostly on time to extract flavors from the coffee bean. Fans of this method like to tout that it’s “low acid,” because the acidic flavor compounds in coffee are more soluble at higher temperatures. That may sound like a good thing—but it’s not.
“A lot of customers are intimidated because they think acidic flavors will be astringent or give them heartburn,” says Josh Brodey, coffee manager at Slipstream in Washington, DC. “But actually, acidity is what defines great coffee.”
Acid gives coffee its bright, fruity flavors—take those away and you’re left with a drink that can taste flat and muddy. Dose it with milk and sugar, and your drink will basically taste like coffee ice cream. Not that there’s anything wrong with that! But you miss the complex flavors that you get from quality coffee beans that are grown and roasted with care.
Flash-brewed coffee, on the other hand, is designed to defeat the true enemy of delicious coffee: oxygen. Chilling the coffee immediately, and then either drinking it right away or storing it in an oxygen-free environment (more on that later) prevents coffee from oxidizing, which also destroys those delicate amino acids that make a great cup of coffee taste delicious.
Cold brew, on the other hand, is often exposed to oxygen for the 12 or so hours it takes for the grounds to steep. Coffee that is brewed hot and chilled gradually has the same problem. But flash brew can be consumed immediately, or preserved for weeks with nitrogen.
Get ready for “nitro” coffee
Slipstream and other coffee shops around the United States are making strides in storing and dispensing their ice-brewed coffee, using the inert gas.
As soon as the coffee is flash-chilled by ice, it is transferred to a keg—the same kind used to dispense beer—which is then infused with nitrogen at high pressure. That keeps it away from the oxygen, and also has a fringe benefit: When dispensed from a tap through a pressurized valve, it is frothy and creamy without needing milk.
It’s the same process used for draught Guinness beer, and nitro iced coffee looks very similar:
The economics of iced coffee
Yes, iced coffee tends to cost more than hot, but why? Some unscrupulous coffee businesses may just be refrigerating their leftover hot coffee and jacking up the price, but for conscientious coffee shops, iced coffee takes quite a bit of time and equipment, which requires charging more.
Cold brew, for example, requires immense amounts of coffee: Often a 1:1 ratio of solids to liquid, compared with a 1:16 ratio for pour-over hot or flash-brewed coffee.
Slipstream, for its part, wants to get “maximum flavor out of minimum volume. That means investing in super-premium grinders so that the coffee particles are of uniform size. It also uses refractometers to calibrate its iced-coffee concentration. And then there’s the cost of nitrogen deliveries.
It all adds up: A 12 oz Slipstream hot coffee costs $2.75; a flash-brewed nitro coffee is $4.50.
“I think $4 to $5 is really not that bad, when you look back at the whole supply chain that gets the coffee to you,” Brodey said. “People have no problems paying $10 for a rail gin and tonic, but when you ask them to pay $4 for a coffee they say ‘This is outrageous!’”
How to make it
If you blanche at the price tag, or want to experiment a bit, it’s easy and cheap to make flash-brewed coffee at home.
For those of us who don’t have a nitrogen tank on hand at home, a very nice flash-brewed iced coffee is possible with just a few pieces of inexpensive equipment: A kettle (ideally one with a gooseneck), a pour-over filter (anything from a Melita to a Chemex), and a kitchen scale.
You also will get the best results if you use a burr grinder and freshly roasted beans from a good supplier—especially lighter roasts with fruitier flavors. But your level of coffee nerdery may vary.
• Put 8 oz (225g) of ice into a large glass, jar, or coffee pot. Heat another 8 oz of water until it’s just off the boil, and pour it over 1 oz (28g) of ground coffee, onto the ice.
• It’s best to first wet the ground and let the coffee bloom (you’ll get bubbles if it was freshly roasted) and then slowly pour in the rest. (This is when the goose-neck kettle comes in handy.)
The resulting iced coffee will be quite strong until the ice cubes fully melt. Drink it immediately, and don’t be surprised if you find yourself wanting another.
And unlike most iced coffee, which goes from flavorful to watery as the ice melts, the experience of drinking a flash-brewed coffee has a robust beginning and a happy ending.
“The first few sips are more caffeine-heavy,” says Brodey. “When it’s diluted more of the nuance comes out. When you’re sucking the last drops of coffee off those ice cubes, I want that to be the most delicious part.”