First of all, let me say that I am predisposed towards iced coffee. My grandfather- who I idolize still- drank iced coffee starting at about 10am, and all day during the summer.
That said, iced coffee has something of a bad name among coffee aficionados. Hot coffee is seen as the natural way of drinking coffee, and iced coffee is thought of as something of an abomination; a way people choke down caffeine during the summer, or a way to make chilly coffee-ice-cream-tasting drinks and sip them with straws out of plastic cups.
I must say that early in my coffee years, I shared the idea that iced coffee was somehow “less than” hot coffee. At that time, we used whatever coffee we had at the end of the day in the urn, put it into a pitcher, and that became the iced coffee for the next day. Later on, we began using the toddy system to make cold-brew iced coffee, which at least had the benefit of not being sour like the day-old iced coffee was. Both were low-end, dead, and without aromatics. That’s just how iced coffee is, right?
Turns out, that’s wrong. When I went to Japan for the first time in 1994, I had iced coffee that was COMPLETELY DIFFERENT. Bright and clear, it had a vibrant, refreshing quality that contrasted starkly with the leaden, low-end iced coffee I was used to in the U.S. And best of all, the aromatics that I was used to smelling in hot coffee, I could taste in iced coffee. How was this possible?
I puzzled over it for years. Finally, I developed a relationship with Hidetaka Hayashi, who is a kind of specialty coffee idol in Japan. One of the first questions I asked Mr. Hayashi was how iced coffee was different in Japan. He taught me a lot over the years, but the thing I figured out was this: many of the iced coffee processes I liked the best brewed coffee hot, then chilled the coffee INSTANTLY by brewing right onto ice. The dilution from the melting of the ice can be taken account in the brew recipe, leading to proper strength and maximum happiness.
Why is this important? Why is this better than cold brew? Well, it has to do with solubility, volatility, and oxidation.
Solubility is the ability of substances to dissolve, in our case, in water. Coffee has soluble constituents; that’s why we can run water through it and the water becomes a solution of coffee solubles and water, creating the beverage we call “coffee”. Now the thing about solubility is this: substances are generally more soluble at higher temperatures and less soluble at lower temperatures. This is why sugar dissolves very slowly in cold water but very quickly in hot water. When we brew coffee, we use hot water to dissolve the coffee solids out of the coffee grounds and into the water, and as we know this happens best at 195-205 degrees Fahrenheit. You can try to use cooler water, but this means that the coffee will dissolve incompletely; many of the soluble substances in coffee won’t make it out of the grounds and into the water. This is what happens in cold brew: the technique tries to make up for the relative insolubility of coffee at cold-water temperatures by brewing for a long, long time. This creates the illusion that you have made coffee- the resulting liquid is dark and tastes something like coffee- but many of the coffee solubles have never made it out of the grounds and into the liquid. Cold-water brewing has a way of deadening flavor, since the elusive and charming elements of flavor that make coffee special never get dissolved into the brew, and remain in the coffee grounds, which get thrown away.
Next: volatility. In contrast to solubility- the ability of materials to dissolve- volatility is the ability of substances to turn into vapor, and be transported through the air. Volatility also increases with temperature: that’s why hot coffee is so aromatic. Problem is, when you’re smelling coffee, it’s losing its aromatics to the air. Cooling the coffee quickly, though, reduces volatility dramatically. This effectively locks the ephemeral volatiles (like floral and fruit notes) into solution until the coffee is warmed again. This happens on the coffee’s way down your throat (sorry to get graphic here), which sends a punch of beautiful volatile aromatics through your retronasal cavity to your olfactory receptors. And that explains the olfactory-flavor punch of brewed-hot-quickly-cooled Japanese-style iced coffee.
What about oxidation? Oxidation in food is generally bad news: oxygen has a habit of monkeying with oils to make them taste horrible, a phenomenon also known as rancidification. You know that funky taste of an unclean coffee hopper or french press screen? That’s oxidized coffee oils. Coffee kept warm takes on these same flavors, since oxidation happens much more quickly at high temperatures. This is another reason why cooling coffee quickly after brewing is essential. Don’t even get me started about chlorogenic acid degradation to quinic acid- which also happens quickly at high temperatures and causes sour bitterness.
So the science tells us: to fully extract flavor? Brew hot. To protect flavor and prevent development of off-flavors? Cool instantly. And what does the method I adapted from Mr. Hayashi’s do? BREW HOT AND COOL INSTANTLY.
Have I convinced you yet that the Japanese iced coffee method is the definitive way to make iced coffee? I hope so. I also hope you enjoy this summer.
