Bitter Exposure

It’s usually a pretty nasty discovery when you pour a cup of coffee from the office coffee pot after it has been sitting a bit too long. 

You know the feeling. You put the cup of hot coffee to your lips, ready to let the warm liquid do its magic to wake you up and get your moving. But instead, the coffee is so bitter you almost gag. On the plus side, you are awake! Just not the way you were planning to get there.

So what happened?

Blame it on too much exposure. 

As I reported in the North Carolina Science Now story, Brewing the Perfect Cup, the roasting of coffee beans generates hundreds and hundreds of new chemical compounds that are locked in the bean and give it all kinds of flavors. That’s why you want to expose the bean to water; to tap those flavors.

Grinding up the bean increases the surface area that will be exposed to the water. Heating up the water helps capture the flavors because the extraction of molecules from a solid happens much faster at a high temperature.

Here’s the catch; the molecules that are extracted first are smaller and very water-soluble, such as acids. The molecules that come out later are larger and not as water-soluble. They tend to be sharp and bitter. And yes, that includes caffeine. Bottom line, if you leave the coffee on too long, more and more of those bitter molecules are extracted.

Caffeine, by the way, is an alkaloid, and humans find most alkaloids bitter. Scientists believe the reason behind that is many alkaloids are toxic and the bitter taste is a warning that whatever you are putting in your mouth could be bad for you. 

I know, you’re probably saying, “But I like coffee and caffeine because they help me become and stay alert.”

That’s true, but when you think about it, too much caffeine isn’t good for you. We’ve simply learned to enjoy bitterness as a flavor and to associate it with the things we enjoy from a cup of coffee, such as flavor and a stimulating effect. Have another cup and enjoy!

- Frank Graff

Frank Graff is a producer/reporter with UNC-TV, focusing on North Carolina Science Now, a weekly science series that airs Wednesdays, beginning in August 2013, as part of North Carolina Now on UNC-TV. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog!


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