Cross-section photos of green and roasted beans can underscore some common misconceptions about coffee.
Some informative details emerge when looking really, really close at coffee, including the unique structure of the coffee bean itself. I take macro images of coffee aka “green coffee
Green coffee refers to the processed seed of the coffee tree fruit. Coffee is a flowering shrub that produces fruit. The seeds of the fruit are processed, roasted,... close-ups” for fun, mostly. There’s no great scientific value in it, but I find it a good reminder of what the coffee bean that we love to roast actually is … what it’s components are, and how these change in roasting.
Lately I’ve taken to bisecting the coffee laterally (with a very sharp blade) to get a different look at the coffee seed.
The Coffee Bean is Folded!
The main thing that always impresses me when I take these “half a bean” images is the fact that a coffee bean is not a solid, undivided thing. The bean has a deep fold that continues into the interior, something like the way some breads and rolls are folded over before baking.
Understanding the structure of the bean demands some context. Coffee beans want to become a plant, not a roasted beverage, after all!
The coffee seed “unfolds” as a small plant. The taproot emerges from the end (Photo 1), the “bean” is elevated on a nascent trunk (Photo 2), and the bean unfolds and divides to form the two initial leaves (Photo 3).
Understanding the coffee seed structure (partly) as nascent leaves helps make sense of the crease and fold in every bean. Here is a diagram of how Coffea
The botanical genus colloquially referred to as the “coffea genus,” which is comprised of over 120 individual species. These are generally opposite-leaved, evergreen shrubs or small understory trees... ArabicaArabica refers to Coffea Arabica, the taxonomic species name of the genus responsible for around 75% of the worlds commercial coffee crop.: Arabica refers to Coffea Arabica, the... root and leaves are formed:
Understanding the parts of the coffee seed better provides some insight as well:
Half A Bean Macro Photos of Green Coffee
From the cherry
Either a flavor in the coffee, or referring to the fruit of the coffee tree, which somewhat resembles a red cherry.: Either a flavor in the coffee, or..., to the viable coffee seed, to the dried parchmentGreen coffee still in its outer shell, before dry-milling, is called Parchment coffee (pergamino). In the wet process, coffee is peeled, fermented, washed and then ready for drying... and then the green coffee bean:
Roasted Coffee Half A Bean Macro Photos
It’s a bit challenging to get a clean cut on the brittle roasted coffee bean. I have done my best here, and there are some unique things that roasted coffee cross-section photos reveal:
Half A Bean and First Crack Acrobatics: A Short Video…
Here’s a short video I made showing the acrobatic coffee beans as they enter the first crackFirst crack in one of two distinct heat-induced pyrolytic reactions in coffee. It is distinguished by a cracking or popping sound in the coffee, and occurs between 390... phase of coffee roasting
The application of heat to green coffee seeds (beans) to create palatable material for brewing a great cup!: Coffee roasting is a chemical process induced by heat, by.... These were roasted on an oven tray so I could capture the transformations of coffee without all the motion of a normal rooster.
You can see the coffee expand a bit just before the it does it’s move. Check out the spin at the end! First crackAn audible popping sound heard during roasting. In coffee, one refers to "first crack" and "second crack," which come from two different classes of chemical reactions.: An audible... occurs when the bound up moisture in the bean reaches the temperature where water turns to steam (water vapor), and suddenly escapes the coffee. This force can visibly enlarge/puff up the coffee, as well as make it move as you see here! – Thompson
11 Responses
Thanks for sharing this video and knowledge, fascinating
Thanks for reading it!!
Nice work. I haven’t seen this complex transformation exhibited before. I’d like to save as a diagram to hang up and reference. Thank You!
Thats a nice idea – maybe we can print this on a color card for that purpose
These are terrific photos, but a small correction: the endosperm is not the “nascent taproot”! Endosperm is a completely separate tissue from the embryo (which contains the embryonic root). Endosperm arises from a different fertilization event than the embryo, has an extra set of chromosomes, and stores nutrients to support the early growth of the seedling.
Thanks for the clarification / correction!
Very interesting photos (and video) with explanations. Thanks for the work you put in to this project.
With a well-roasted bean should the cross section show a fairly even darkness or does some variation of color add to the flavor?
This is a great question, and really depends on the roast. With light roasted coffee, if you roast it too fast, the exterior is likely to be much darker than the interior. Too long a roast will develop a much more uniform coloring, but may come at a cost of “baking” out acidity and sweetness. When we judge our own roasts – especially light roasts – we find that grinding the coffee gives a much more accurate representation of roast coloring since it’s an amalgam of both interior and exterior.
Good question.
Dan
It’s a good question! The degree that color tracks with the changes in compounds developed in roasting, and those compounds impact the cup, yes there seems to be something to learn from variation in bean color from inside to outside in the photos. What I have always done to try to understand a roast better is visually check the exterior bean color of whole bean roasted, vs. the color of ground coffee placed next to it. The difference between them can give a rough idea how the roast process is doing roasting the coffee interior. Slow drum roasts, like from our Probat 12 kg, would show less difference in color between whole bean and ground coffee. Faster air roasts would have a greater difference. In the cup, this could mean more balance (perhaps nicer espresso) from the drum roast. But it could also flatten out the cup … whereas the air roast would be more dynamic, higher high tones, more vivid in brewed coffee. A “bad” drum roast would be baked and flat, a “bad” air roast would have raw grain flavor and a harsh acidity. But each process done well has it’s strengths, and all this correlates roughly to that color variation (or lack of) from bean interior to exterior.
This is really awesome, thanks for sharing!