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Food Ingredients


Hating vegetables, loving cold coffee

by Melody M. Bomgardner
January 27, 2019 | A version of this story appeared in Volume 97, Issue 4


Bitter gets better

A young boy makes a face of distaste with lettuce on his fork.
Credit: Shutterstock
Bitter bites: Have faith, kid; it'll taste good . . . eventually.

The end of January is traditionally when people abandon their New Year’s resolutions. But Newscripts is hanging in there, staring down a plate of—what is that, kale?—in pursuit of that holy grail of healthfulness, the plant-based diet.

One good reason to carry on, cruciferously, is that humans can overcome their instinct to turn away from bitter foods over time. In short, it gets better. Routine exposure can even foment a love for bitter flavors such as dark chocolate, hoppy beer, and even leafy greens.

Researchers want to know how we acquire a taste for bitter food compounds like healthy polyphenols in plants. One secret may be in our saliva. Studies by Cordelia Running, a professor of nutrition and food science at Purdue University, suggest proteins in our saliva change over time in ways that may alter how those foods taste.

Running conducts human taste experiments at her SPIT lab—that’s short for saliva, perception, ingestion, and tongues. “There is not a lot of knowledge out there on the way that saliva functions,” she says, adding that the chemistry of the mouth is a “big black hole” research-wise.

Saliva is around 99% water, but in addition to H2O, spit contains enzymes and proteins that interact with molecules in our food.

Human subjects in Running’s lab drank 237 mL (8 oz) of chocolate milk three times a day for a week, and their saliva was analyzed over time. She reports that the amount of proteins rich in the amino acid proline increased in the samples. Experiments done outside the mouth have shown those proteins can bind to and precipitate out bitter compounds in red wine and chocolate.

Running suspects the chemical interaction might waylay bitter compounds, sending them down the gullet before they can touch down on the bitter taste receptors on the tongue.

Humans evolved a wariness of bitter tastes because they often signal the presence of bioactive compounds, which can be nutritious but can also be poisonous. Researching changes in spit can help differentiate the various ways we get around our distaste for bitter compounds, says Steven D. Munger, director of the University of Florida Center for Smell and Taste. Already, scientists know that when we learn to associate bitter flavors with positive effects such as a happy dinner with family, the rush of caffeine, or a buzz from beer, it can change our opinion of bitterness, he points out.

Taste science has shown that the more times you experience a bitter food, the better the response. Though Running admits that no matter how many of them you eat, “Brussels sprouts will never taste like chocolate cake.”


Cold coffee myths

A wood frame holds glassware for a high-tech cold-brew coffee system.
Credit: Shutterstock
Cool beans: What is your barista extracting in her cold-brew coffee contraption?

Complain about the bitter taste of coffee, and a millennial might pipe up to suggest a cold brew. Proponents say the chilly stuff is smoother—less acidic and less bitter—and has more healthy polyphenols than that hot swill consumed by the olds.


Niny Z. Rao, a chemistry professor at Thomas Jefferson University, is passionate about coffee. But her first effort to make cold brew at home came out “just awful,” she said. Rao figured her undergraduate research students could fix her technique and at the same time find out if those café chalkboard science claims could be proved in the lab.

Rao’s students hypothesized that the different water-extraction techniques of cold versus hot coffee would result in different amounts or types of acidic and bitter compounds. “On Tuesdays and Thursdays, the hallways smell wonderful,” Rao tells Newscripts.

Rao’s group found that the pH of the two brews is comparable. But pH does not measure levels of non-deprotonated acids, which the students found to be higher in hot coffee after they titrated their samples with a strong base. In the mysterious chemical environment of the mouth, those could be the acids that people are tasting, Rao explains.

The research team also found cold brew is lower in bitter antioxidants, including caffeoylquinic acid isomers. So yes, cold brew really is less acidic and bitter, but it’s comparatively lacking in the polyphenol department. Sorry, hipsters.

Melody Bomgardner wrote this week’s column. Please send comments and suggestions to


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