How Temperature Can Make Or Break Your Cold Brew

Lately, I've been into cold brew coffee. It's not just the summer heat — the method is just so easy. I scoop the coffee into a reusable filter, plunk the filter into a carafe, and let it steep in the fridge overnight. But, according to Donny Raus, founder of Raus Coffee Company, there's a better way to do it. Raus is a certified coffee sommelier (aka a Q-grader) who shares advice on Instagram.

Raus told The Takeout the optimal temperature for cold brew isn't actually cold. When he makes cold brew, he prefers room temperature. "Temperature is the main driver behind extraction," he explains. "Coffee extraction happens over a range of temperatures. The higher the temperature, the more extraction." 

"Cold brew is similar," Raus continued. "The amount of extraction will increase with temperature." In other words, making cold brew in a fridge set at 37 degrees Fahrenheit versus the open countertop will have a big impact in terms of how your cold brew tastes.

In addition to the extra-strong caffeine punch you get with cold brew, it tends to have a smooth flavor. That's because some of the molecules that are extracted at the high temperatures of a standard brew get left behind. The cold brew process helps keeps bitter flavors out, so long as you don't let the beans soak too long.

Technically, cold brew coffee isn't "brewed." Unlike iced coffee, it's steeped. To make cold brew, simply combine ground coffee and water in a container and wait. I use a large, basket-style tea infuser, but you could just as easily dump the coffee straight into the water and strain it once it's done. Different coffee-to-water ratios will produce different flavors, strengths, and caffeine contents. You'll typically use more coffee this way relative to a standard brew, but the right ratio will depend on personal taste. A 1:4 ratio is a good place to start; adjust from there. 

While Raus prefers countertop extraction, he admits it's not always the best choice. "If your room is hot and humid, I don't advise brewing on the countertop," he explained. Coffee brewed at room temperature can mold, just like sun tea. Even if your place isn't hot and humid, he urges caution. "If brewing on the countertop you must make sure you use a very clean vessel, control your ambient temperature, and don't go beyond 24 hours," he said. If countertop cold brew isn't an option (or if you simply prefer a mellower flavor), you can still use the fridge. Just remember that the colder your cold brew is, the longer you'll have to wait. "If you're going to brew cold brew in a refrigerator, the hold times should be longer," said Raus. "When I use this method I go out 48 hours." 

Raus recommends matching your cold brew technique to the beans. He says that light roasts (which tend to have subtle, complex flavors) are better suited to countertop extraction. Why can't you use the fridge? "You won't get the extraction you're looking for," Raus explained. He added that the coffee "may taste tea-like." But, if you're looking for a way to use up a bag of dark roast, a fridge-brewed method could be the right fit. 

If you want to speed up the process, Raus recommends a finer grind. "Grind fineness is going to be a major consideration for how long you brew cold brew," he said. "Fineness aids in extraction because more surface area is exposed to the water. As a result, you can grind finer and brew for a shorter period of time or keep time consistent for a more concentrated brew." Want other ways to up the extraction? Check in periodically while your coffee is brewing to give the grounds a stir. 

But according to Raus, you don't need to stress about grind size that much. Just don't go to extremes and you'll be fine. Ultra-fine grounds can make cold brew muddy, while an extra-large grind will limit extraction. "Cold brew is very forgiving for variables such as these," he says. Serve your cold brew over ice and top it with milk or sweetened condensed milk. In the mood for something fun? Try mixing cold brew with lemonade.