Hot and Cold Brew Coffee Are Chemically Different, Study Says

If antioxidants are all you're after, hot brewed coffee may be the better choice.

Cold brewing and hot brewing clearly creates different coffees—and not just when it comes to temperature. You may have noticed this if you've cooled down a hot coffee (a.k.a. iced coffee), and found it tasted different than a cold brew. So are there chemical differences between hot brew and cold brew coffee? According to researchers at Thomas Jefferson University, not a lot of science has delved into this subject—in part because cold brew has been a more recent trend—but it's something they've been trying to get to the bottom of. And recently, they specifically looked at the role different roasts play in the results.

For their study, the researchers compared factors like the levels of acidity, antioxidants, and caffeine in both cold and hot brewed coffee in a range of roasts from light to dark. Interestingly, caffeine might be the first thing many people think of when grabbing a cup of coffee, but this study found little difference in caffeine levels across roast or temperature other than that hot coffee typically had slightly higher caffeine levels than cold brew, and light roasts had slightly higher levels of caffeine than dark roast. Instead, the biggest differences were in antioxidants and acidity.

Delicious black iced coffee
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"Hot brewing extracts more antioxidants from the grind than cold brew, and this difference increases with the degree of roasting," Niny Z. Rao, the project's principal investigator, explained in announcing the results through the American Chemical Society. In other terms, hot brewed coffee seemed to have a constant level of antioxidant activity regardless of the roast, whereas the antioxidant activity in cold brew coffee was a bit lower for light roasts and continued to get lower as the roast became darker. As a result, in theory, Rao says a hot brewed dark roast coffee may be healthier than a cold brewed dark roast coffee.

But cold brew coffees also had less acidity. "Cold brew coffees across all three roast temperatures were slightly less acidic than their hot brew counterparts," the results state. "As roasting temperature increased, the total titratable acidity (TA) of all coffees decreased. With an increase in roasting temperature, an increase in the TA differences between cold and hot brew coffees was also observed to increase slightly, indicating that roasting influences extraction processes."

So what does all this mean for consumers—people who drink coffee, not chemistry? "My advice to consumers has always been to drink what they like," Rao summarized. "But if you want to craft a coffee beverage with antioxidants or acidity in mind, you may want to pay attention to roast. If you want a low-acid drink, you may want to use a darker roast. But remember that the gap between the antioxidant content of hot- and cold-brew coffee is much larger for a darker roast."

That said, it's also important to know that, though cold brew is usually made with coarse grinds, to make sure they were comparing apples to apples, for their study, the researchers used medium grinds for both hot and cold brewing. (It would be interesting to see comparisons between these drinks when prepared using less scientific and more traditional methods.)

Still, the conclusion in the abstract of the study is very straightforward: "The results suggest that the bean roasting temperature significantly impacts the chemistry of the final coffee brew and should not be ignored when crafting cold brew coffee beverages." By the way, the roast impacts the taste, too, which—no offense to science—is also something not to be ignored!

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