Brewing coffee in high volume and then cooling in the fridge to satisfy a café's rush hour demands, or a week's worth of commuter travel mugs, is not the way to go. Refrigerating coffee promotes rapid and prolonged oxidation over time, doing irreparable harm to coffee's essential, aroma-harboring oils, accompanied by fast-escalating acidity. Two recipes for disaster.
The longer the cooling time, the greater the breakdown of harder-to-detect complex acids into simpler acids our taste buds perceive more readily. Darker roasts can help counter this breakdown to a degree. But the espresso-based rapid cooling method is the best way to maintain balance and fight sourness.
There is another way. Though not new, it's being newly rediscovered, and becoming something of a movement. Actually, make that two closely related ways: cold brewing and cold steeping. Each can produce stellar results.
Cold brewing and cold steeping rely on time rather then heat to transfer coffee's substances into water—a completely different kind of extraction from hot water. There are tradeoffs, because numerous substances in coffee can't be fully extracted without heat—most notably oils and certain aromas. But cold methods also giveth, by extracting fewer acids than heat-based infusions. The result is somewhat less aromatic but very clean—an almost sweet concentrate, neither acidic nor bitter. As with hot infusion, major variables impacting taste are the coffee's contact time with water, fineness of grind, and amount of ground coffee used.
As in hot coffee preparation, there are two "families" of cold extraction: infusion and percolation, which is also called transfusion. Cold steeping is extraction by infusion. Simply mix cold water and ground coffee, steep in the fridge for up to 12 hours, then strain and filter. It's quite similar to the traditional French press, and indeed a press pot serves cold infusion well. Remember to gently stir the coffee before placing in the fridge, and don't press down until the cooling is complete. Use a coarser grind—more readily trapped by the filter in a French press pot—and don't be stingy: you'll need about six times the usual one gram of coffee per one ounce water of recommended for hot French press preparation. Gear lovers can also find dedicated cold infusion devices, like the Toddy coffee maker, which has been around since the '60s.
Cold brewing is filter coffee's stone-cold brother, requiring special gear ranging in price from $45 into the hundreds of dollars. (Some adventurous types rig up their own cold brewers and spend nothing.) Picture a tall glass tower with multiple chambers and filters. Ice-cooled water drips from the upper part of the tower, where a special valve and a spiral-shaped pipe regulate the speed of the drops, ideally one per second. The drops run over ground coffee housed in a clear cylinder covered by thin tissue or a paper filter. Underneath, another filter prevents ground coffee from entering the next section of spiral pipe, from which finished, brewed coffee drips and collects in the tower's base. Cold brewing takes time—about 12 hours—so it's best done overnight. You might save a little time by using a coarser grind, and be willing to tolerate a less aromatic coffee.
With beautifully balanced, aromatic, chilled coffee as foundation, the power to create iced coffee perfectly suited to your tastes, and summertime whims, is all yours. Take inspiration from your favorite stop along the world tour we took earlier. Experiment with your shaker, with ice cream, liqueurs, sweeteners. Or, with nothing at all. Prepared correctly, starting with high quality, properly stored beans, your coffee will hold its own—even on the rocks.
Images (top to bottom): thebittenword.com/flickr, INeedCoffee / CoffeeHero