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Uploaded:2017-05-06
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Like it or hate it, cold brew coffee definitely tastes different than regular ol' drip, and it's all thanks to science.

Hosted by: Hank Green

Learn more about making coffee at youtube.com/learnhowtoadult
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Sources:
http://www.scaa.org/PDF/CoffeeBrewing-WettingHydrolysisExtractionRevisited.pdf
http://legacy.sweetmarias.com/coffee_chemistry/tweaking_coffees_flavor_chem.html
https://scienceandfooducla.wordpress.com/2014/08/19/coffee-brewing-chemistry-hot-brew-and-cold-brew/
http://www.bunn.com/sites/default/files/brochure/coffee_basics_scaa.pdf
https://blog.intelligentsiacoffee.com/2017/01/17/extraction-theory-and-you/
https://www.beanscenemag.com.au/articles/view/socratic-coffee-explains-why-size-matters-part-iv
http://cen.acs.org/articles/93/i33/Nitro-Cold-Brew.html
http://theconversation.com/the-perfect-cup-of-coffee-boils-down-to-four-factors-30208
If you’ve ever tried a cold brew coffee, you might’ve been surprised that it tasted so different from regular coffee —even different from iced coffee.

Maybe you enjoy its sweeter, less acidic profile— I know I do, although I don’t drink coffee very much because I am jittery enough without caffeine, thank you very much. But maybe you think cold brew tastes kind of boring.

Either way, it is different. Cold brew coffee is brewed by putting coffee grounds in water that’s room temperature or even colder, and then letting it just sit there for hours or days. That changes the taste because temperature is super important when it comes to the chemistry of coffee.

When you mix coffee grounds with water, all the fun stuff in the beans that make up coffee flavor— acids and sugars, and yes, caffeine— get pulled into the water. That new solution is what we call coffee. Most brewing methods use hot water that’s around 93 degrees Celsius because most of the components we know and love in coffee are quickly and easily extracted at that temperature.

Hot water has more energy, so it dissolves things more easily, speeds along the diffusion of molecules from inside the beans out into the water, and accelerates the chemical reactions that break down compounds when they come into contact with water. All of that means lots of flavor in a matter of minutes, whether it’s espresso, French press, Chemex, or just plain drip. Traditional iced coffee is made from hot-brewed coffee that’s cooled down, usually just by pouring it over ice.

Cold brew, on the other hand, trades temperature for time. Since the water isn’t hot, extracting deliciousness from the coffee grounds takes a lot longer. And while you’re probably getting most of the same compounds, you’re not getting the exact same ones, or the same amounts.

Some bitter plant molecules, for instance, take a lot longer to extract, or need higher temperatures, which could explain why a lot of people say cold brew tastes smoother and less bitter or acidic. Water temperature also plays a role in how quickly certain molecules are broken down or degraded after the coffee’s been brewed. One big complaint about hot coffee, for instance, is that it gets sour if it’s been sitting out for too long.

That’s from compounds reacting with oxygen in the air and from the water. Heat speeds up those chemical reactions, which is why you can barely choke down stale coffee that’s been on a hotplate for five hours in a diner. Cold brew will eventually go stale, too, but with no heat in the mix, you’re less likely to have that problem.

So, there are lots of reasons why a simple change in temperature will change the taste of coffee. And whether or not you’re a fan of cold brew probably depends on what you like most about coffee in the first place. I like for it to taste like chocolate!

Thanks for asking, especially to all of our patrons on Patreon who keep these answers coming. For tips on how to actually make coffee, and all kinds of other adult-y stuff, you can check out our sister channel How to Adult at youtube.com/learnhowtoadult.