Roasted Coffee Comparison: Surface Color and Texture Versus Ground Samples

Judging roast from whole bean is hard: Try grinding the coffee to compare the roast level!

The exterior and the interior of the roasted coffee bean might be holding valuable information in terms of their color and appearance.

Here is a comparison between roasted coffee surface color, surface texture and ground coffee samples.

What you can see is that this coffee, our special 2006 selection of Costa Rica Peaberry from Dota, Tarrazu, has a lot of surface color patchiness, and a lot of surface texture at the lighter City roast (first crack completed, roast progress stopped immediately, 426 degrees finish temperature as measured on the Probat L12 roaster. Keep in mind these pictures are taken under 4 strong lights on my photographic copy stand, so in “normal” lighting the surface blotches would not be so extreme, and the overall roast colors would look darker.

Costa Rica Peaberry - 3 roast levels compared surface versus ground coffee
Costa Rica Peaberry – 3 roast levels compared surface versus ground coffee

Surface texture influences how you perceive color. So even the fineness of grind influences color perception. Notwithstanding, ground samples provide a much clearer method of evaluating color, which is why roasters use ground samples when implementing a color measurement system like Agtron, or the like.

The light source, both its intensity and reflectivity, are very important to judge coffee. The color balance of the light source is important too, especially as “warmer” light tends to lead to an impression of darker browns.

Costa Rica Peaberry 3 Roast Levels Surface Appearance of Coffee
Costa Rica Peaberry 3 Roast Levels Surface Appearance of Coffee

Here are swatches taken from the same photo above. Note the extreme difference in patchy surface color from lighter to darker roast. This specific lot of coffee is quite nice at the darker roast levels (pungent spicey/pepper notes with intensely tangy bittersweet chocolate).

But it is at the “ugly” City roast where this coffee has true Dota Tarrazu “origin character”, i.e. winey fruited notes with interesting almond and hazelnut roast taste, grape, grape skins in the finish, cherry. Roasting is not a beauty contest, and many commercial and home roasters make the mistake of roasting coffee until surface texture is even, and variation from seed to seed is more uniform.

You need to roast it for cup flavors, not for roasted coffee appearance. What that specific cup character is, you decide. But at the Vienna roast pictured above (448 f finish roast temperature in the Probat L-12), tangy roast notes have eclipsed the “origin flavors” of the coffee.

I would also say that this lot of our special peaberry selection is less uniform than even I expected … but I was happy with the cup, and that is what counts! Coffee makes your constantly overcome your prejudices and re-evaluate your own “received wisdoms” when it comes to judging cup flavors.

While roast level can be hard to judge empirically, you can create your own set of saved samples and use them for future roasts. It’s a better way than buying a $4000 color analyzer or a set of SCAA Agtron roast color disks:

Coffee roasting color tiles disks SCAA Agtron
Coffee roasting color tile degree of roast disks SCAA Agtron

-Thompson

Here are some other pages discussing degree of roast:

Using Sight to Determine Degree of Roast

6 Responses

  1. I am kind of a novice, but am really enjoying your beautiful and informative website. Thank you very much!
    Steve in Rohnert Park

    1. Thanks for the note Steve! I’m glad to hear your finding our site useful and informative. Don’t hesitate to drop us a line if you have any questions.

      Cheers.
      Dan

  2. I come back to this site often to review and keep myself up on coffee knowledge. This is, in my opinion, the best that can be found on the internet. Thanks so much for sharing with us who want to understand and experience the best coffee we can brew. I seem to be a perpetual coffee novice but keep trying to get to that perfect cup of coffee. Roasting will probably be my next adventure. I have my doubts that I can equal what the professionals accomplish, but I want to try.

    1. Carlos,
      All I can say is, don’t wait any longer to start roasting! (after a couple of tries) you won’t believe what an amateur can accomplish!

  3. Always appreciate what you do.
    I have a question. You show color and temp of the bean while going through the roasting process. How do you measure the bean temp?

    1. Usually we are using a thermocouple probe. Like this: https://www.sweetmarias.com/k-type-thermocouple.html
      It is used with a digital thermometer, which we are actually out of stock on, but it will be back in a week or so…
      This type of probe, when placed directly into the coffee mass while roasting is really responsive … but they don’t last as
      long as the type that is inside a metal housing. Those types tend not to be as responsive.

      Anyway, they key thing here is that we are measuring a contact temperature, and that’s always going to be a little variable, because it will be measuring the environment too. Some people talk about “bean temperature” but there isn’t a way to measure what is happening internal to the bean during roasting. You can use a no contact IR thermometer, which can work well too, but you have to hold it and aim it at the coffee….

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