Thursday, March 30, 2006


coffee is sweet

you know, i had the opportunity to chat with coffee science guru and scaa pro member carl staub of agtron the other day. one of the many interesting things we discussed was a question that had long intrigued me.

as you all know, dear readers, coffee beans are in general 7-8% sucrose. that is, coffee is naturally sweet, which isn't surprising, since sucrose is widely found in plants.

so why do people normally experience bitterness in otherwise well-grown, well-processed, and properly roasted specialty coffee? shouldn't all coffee taste as sweet as an apple?

carl's discussion of this focused on the chemistry of the sucrose in the roast. as the green coffee beans heat up, the sucrose in the coffee splits apart, releasing water, etc.

this is the source of what is known to roasters as "first crack," and if you've ever roasted, you've heard it, a kind of pop-corn-like pop. not to get all technical (like i did last night on my poor coffee meetup group), in fact to massively over-simplify, the saccharides come up to the surface of the bean where they can get all nice and caramelized.

yummy. but if the temperature during roasting isn't exactly in the right range, these sugar products turn into molecules we poor humans can't taste, and so we lose the beautiful sweetness of the coffee. this is why coffee roasting remains an art despite scientific advances in coffee chemistry and roasting equipment.

because only the pro roaster/cupper can taste the sugar! i found this such an interesting conversation that i continued it with a long-time bccy pal and member of the roasters guild, barry jarrett of riley's coffee (hint, think the famous decatur street espresso blend).

here's what barry wrote to me, with old-school ascii art! fun!

thanks barry for permission to quote ya:

"taste perception is based on molecule shape. it is possible for some molecules to form configurations which have different characteristics even though they are the same molecular formula (the one i remember best are cis- and trans- configuations). let's see if i can do some ascii art:


O=C-C=O
  | |
  H H

that would be cis-
  H
  |
O=C-C=O
  |
  H
that would be trans-

sometimes these formations are only obvious when looking at a 3-D model of the molecule.

anyway, the point is that molecules of the same formula can behave differently, and sometimes it's just a matter of energy input in determining the shape of the molecule. if sucrose is fractured (i think the proper term is 'decomposed' but people get weird when using that term), then it no longer behaves like the sucrose we know and love too much.

so, my take on what you've related is that during roasting, the physical structure of sucrose depends upon the energy levels at the molecular level. if the literal 'sweet spot' is missed, then the available sucrose is rendered into a form which is structurally incompatible with the sweet taste receptors on the tongue, and the potential/inherent sweetness is lost."

see, coffee lovers, chemistry, which at first can seem quite arcane, is really very enlightening when it comes to questions about our favorite beverage!

and this is why we are seeking are those artisan roasters who know the secret -- gained only from experience -- of roasting coffee to keep those sugars in a shape we can taste. . .

but for those of you who just can't deal with this much science, please enjoy a charming article on belgian chocolate.

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