Scientists identify roasting as the main culprit of bitterness in coffee

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Abe Carmeli
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Postby Abe Carmeli » Apr 01, 2012, 10:41 am

A recent study by German scientists may show the way to a better roasting profile.

"Roasting is the key factor driving bitter taste in coffee beans. So the stronger you roast the coffee, the more harsh it tends to get," Hofmann says, adding that prolonged roasting triggers a cascade of chemical reactions that lead to the formation of the most intense bitter compounds.

Using advanced chromatography techniques and a human sensory panel trained to detect coffee bitterness, Hofmann and his associates found that coffee bitterness is due to two main classes of compounds: chlorogenic acid lactones and phenylindanes, both of which are antioxidants found in roasted coffee beans. The compounds are not present in green (raw) beans, the researchers note."

"Now that we've clarified how the bitter compounds are formed, we're trying to find ways to reduce them," Hofmann says. He and his associates are currently exploring ways to specially process the raw beans after harvesting to reduce their potential for producing bitterness. They are also experimenting with different bean varieties in an effort to improve taste. But so far, none of these approaches - details of which are being kept confidential by the researchers - is ready for commercialization, he notes.

But the researchers are optimistic that a better cup of Joe is just around the corner. Perhaps no one could be happier about the news than Hofmann, who admits that he is an avid coffee-drinker with a passion for the dark-roasted varieties."
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Postby RapidCoffee » Apr 01, 2012, 11:17 am

Abe Carmeli wrote:"Roasting is the key factor driving bitter taste in coffee beans."

I would think the solution is obvious. :lol:

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Postby Abe Carmeli » Apr 01, 2012, 11:22 am

We should all go green :).
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Postby tekomino » Apr 01, 2012, 11:25 am

And (un)related scientific panel finds out that main culprit in getting wet is exposure to water!
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Postby rpavlis » Apr 01, 2012, 3:48 pm

Chlorogenic acid, by the way does NOT contain chlorine. None of the molecules that they say cause bitterness contain nitrogen. There are amazing computer programs available today, I just generated the image below using two programs one called obgen to generate the position of atoms, and another called vmd to display the atoms. Amazingly the program got the 3 dimensional structure correctly. Programs to do this are now free, they formerly cost thousands of dollars.


The cyan atoms are C, the white H, the red O.

The compounds they describe are derived from this. This compound is present in lots of plants without roasting them, but the bitter compounds apparently are modifications of this. (Rings form with the acid group on the lower right, with some of the OH groups.)

The many -OH groups on this molecule and its derivatives mean that they bind strongly to things--like the coffee grounds. One would expect things like this to elute from the grounds fairly slowly, so this would result in "long" shots being bitter, whilst short ones should be much less so. (Which is the case.)

Understanding details of things is the secret to being able to improve things and fix problems that arise.

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Postby another_jim » Apr 01, 2012, 6:09 pm

Greeen coffee has extremely bitter and astringent compounds too. Just steep some and see for yourself. Presumably, there is a stage just at the end of the first crack where coffee is mininmally bitter, having broken down the trigonellene and other green bitters and not created the furfurines and other roasty bitter compounds ("dry distillates" on the tasting wheel). When roasting to this level, bitterness is simply not an issue.

So I think the research may be aimed more at reducing the bitterness of darker roasts by preventing the formation of distillates while retaining the caramels.

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Postby Sherman » Apr 02, 2012, 1:05 am

Well played, Mr. Carmeli. Welcome back, BTW. :lol:
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