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upstart writes in with an IRC submission for SoyCow8192:

The chemistry of cold-brew coffee is so hot right now:

Cold-brew coffee is so hot right now, and not just with hipster consumers. Scientists at Thomas Jefferson University in Philadelphia have been taking a deeper look at the underlying chemistry to better understand how the cold-brew method alters coffee's chemical characteristics, with an eye toward pinpointing the best way to cold brew the perfect cup. They had originally planned to present their results last month at the American Chemical Society meeting in Philadelphia, but the COVID-19 pandemic shut that down. So instead, they presented the information in a virtual poster session.

[...] "It turned out that there is a lot of research on coffee but not much research on cold-brew coffee," said Rao. That's partly because the biggest coffee-brewing countries (Italy, Turkey, Brazil, Colombia, for example) are all devoted to hot-brew coffee, like espresso. The cold-brew trend is mostly centered in North America.

"There are a lot of studies on espresso," said Rao. "We thought it would be a good idea to put some information out there for consumers and enthusiasts like me who want to make their own cold-brew coffee."

In one paper, published in 2018, Rao and Fuller measured levels of acidity and antioxidants in batches of cold- and hot-brew coffee. But those experiments only used lightly roasted coffee beans. The degree of roasting (temperature) makes a significant difference when it comes to hot-brew coffee. Might the same be true for cold-brew coffee? To find out, the pair teamed up with one of their undergraduate students, Meghan Grim, to explore the extraction yields of light-, medium-, and dark-roast coffee beans during the cold-brew process.

[...] For the lighter roasts, Rao et al. found that caffeine content and antioxidant levels were roughly the same in both the hot- and cold-brew batches. But there were significant differences between the two methods when medium- and dark-roast coffee beans were used. Specifically, the hot-brew method extracts more antioxidants from the grind; the darker the bean, the greater the difference. Both hot- and cold-brew batches become less acidic the darker the roast. An academic paper on the results is forthcoming.

"My advice to consumers has always been to drink what they like," said Rao. "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."

Next, Rao and her colleagues plan to extend their research to exploring how the cold-brew versus hot-brew processes and roasting temperatures affect the flavor compounds in raw coffee beans, called furans. "I was hoping to finish that project by now, but, well, the pandemic put a ding on that plan," she said. "The [university lab] building is completely shut down." As for home experiments, cold-brew requires significantly more coffee than the hot-brew method, and her household is rationing the precious coffee supply just like everybody else.

Previously:
Differences Between Cold and Hot Brewed Coffee
How Cold Brew Has Changed the Coffee Business

[Ed Note - Added links to previous stories.]

Original Submission