With temperatures rising as summer heat waves kick in, a cup of iced coffee or cold brew has likely graced your hands in recent weeks. There’s nothing quite like that first sip touching your tongue ahead of a long weekday in the summer.
But hot coffee that has cooled naturally doesn’t have the same smooth taste — even if it’s brought to the same temperature. Seems weird, right? Why wouldn’t coffee taste the same at the same temperature, even if it got there another way?
We asked coffee experts to explain, but before we get into the why, we’ll lay out the types of coffee we’re discussing here:
- Iced coffee: Coffee brewed hot that has been cooled rapidly or has ice added immediately.
- Cold brew coffee: Coffee grounds are steeped in water between 12-24 hours and then strained over a coffee filter to make cold brew concentrate that’s diluted with water or milk and served over ice.
- Naturally cooled hot coffee: Coffee brewed hot that’s been gradually cooled to room temperature without using ice.
Back to the coffee conundrum, as posed on TikTok: “Why does intentional cold coffee delicious but warm coffee that has gone cold (is disgusting)?” @bottomlysmimosas posed.
Dan McLaughlin, “@softpourn”, answered her question directly in a stitch.
A chemical reaction is what makes hot coffee that has cooled gross
McLaughlin, who has been working in coffee since he was 15 and is the owner of Cleveland-based Golden Triangle Coffee, said in his video that it’s a chemical reaction that causes the coffee that was once hot and has become cold to turn icky.
Scientifically, there are a number of factors why coffee changes flavor so much while naturally cooling but lactones are the “leading reason,” McLaughlin told USA TODAY.
“As hot coffee cools, these lactones break down to become carboxylic and chlorogenic acids. These acids present themselves via a bitter/acidic flavor in the cup,” he said. “This combined with the oxidization that is also occurring as coffee cools down just makes for a super unpleasant taste most of the time.”
McLaughlin said that coffee that is “flash chilled” such as iced coffee — which means that the coffee doesn’t have time to cool down naturally (which is when the lactone breakdown occurs) — or cold brew, which is never hot — don’t generally have those same chemical reactions taking place because there’s no starting point for the breakdown to happen.
Will Frith — who wears many hats including coffee consultant, roaster and founder of Building Coffee located in Ho Chi Minh City, Vietnam — said cold brew are more “stable” since the temperature remains in the same range from beginning to end.
Heat causes aromas to leave the coffee over time, he added, noting that iced coffees keep aromas intact.
“The main difference between hot and cold brewing is extraction efficiency – heat aids with speed of extraction, and the proportion of flavor molecules (salt, sweet, sour, bitter, umami) varies between the two,” he said.
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Coffee quality matters, too
On occasion, McLaughlin said, the chemical change can taste good to some people — if the coffee is a better grade.
“Along with that, a higher quality, freshly roasted coffee can sometimes be complimented by the breakdown of lactones and the acidity it brings to the cup,” McLaughlin said. “But it’s definitely a matter of taste.”
Frith added that some coffees actually improve in taste as they’ve cooled more and we can sense the coffee’s natural sweetness better.
“Our tongues sense most effectively when things are at or near body temperature, so when a hot coffee ‘stops’ tasting good at room temperature, it’s because it wasn’t great to begin with,” Frith said.
And a higher temperature actually distracts from the fact that it was a bad cup of coffee to start with.
“The heat, plus volatile aromatics (aromas that dissipate into the air as steam carries it away from the beverage), distract our senses enough so that it ‘tastes’ good at higher temperatures,” Frith continued. “Nearly 80% of what we perceive as flavor is actually aroma.”
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