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Aromatic Milestones – The Basic Coffee Roasting Skill

Using aromatic milestones, you can roast without any logging software or theoretically even without a thermometer (although I don’t advise it) as they mark certain progress in the coffee roasting process. You can identify them all the way until the first crack. As the name suggests, this approach uses your sense of smell to identify stages in the roast, fragrances reminding you of freshly cut grass, hay and baking bread. And then there is that A-point, the very short moment just before the first crack. This is the first time the coffee reveals its true aromatic potential. Willem Boot developed these milestones to help his students understand the progress of the roast.

The temperatures when these aromatic milestones happen are only indicators. Each coffee is different, according to its processing method, cell density moisture content and other attributes. Also, do not forget that bean temperature is only an approximation and depends where the probe is placed in the roaster. Roasters also don’t apply heat in the same way, so the aromatic milestones will occur at different temperatures.

How about you? Do you use these or other aromatic milestones? Would you be able to create the roast you want only using aromatic milestones and a timer? Let us know in the comments below.

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Wet Grass

200-240° F (93-116 °C) Water is changing from its liquid state to gas. It is the first indication that the applied heat is affecting the coffee bean. Water wapor is leaving the beans.

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Hay

290-320° F (143-160 °C) Maillard reaction starts while the color changes from green to the first shade of brown. This indicates that the sugars start caramelizing.

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Wet Grass

330-355 °F (165-180 °C) Maillard reaction continues as the color changes to darker shades of brown and almost all free moisture is evaporated.

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A-Point

360-375 °F (182-190 °C) At the onset of the A-point aromatic properties of the coffee can be smelled for the first time.The A-point occurs right before the first crack and it indicates that more complex chemical reactions are about to start.

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First Crack

First crack is not an aromatic milestone but a consequence of them. First crack marks the beginning of the “RD” – roast development time. it is time which is also called “stop posting stuff on Facebook and focus” (BTW you should not have done it even before). The chemical changes speed up and the roaster has to monitor the development very closely.

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April 2, 2015

6 responses on "Aromatic Milestones - The Basic Coffee Roasting Skill"

  1. Prior to the A-Point it should read “baked bread”. I guess there’s a copy & paste error.
    The pictogram for the blog entry shows the correct milestone.

  2. Is there a recommendable or desirable duration between each sensory milestones?

    And if I couldn’t sense a strong, distinctive sensory milestones, did the roast go wrong? With my small roaster(1 kg, 500g batch roast), when I tried high heat and fast roast, the sensory milestones were very weak and vague and the result was under-developed roast.

    • Not really. It depends on the roast profile, but we recommend that the first crack on regular drum roasters should start around 10min.

      Do you log your roast somehow? Can you post a picture of a chart or describe times you getting? Also what kind of roaster do you use? It will help me to better understand the problem.

      • Thanks for kind reply.

        FYI, it’a 1 kg drum roaster with a damper and a cyclone for chaff removal.

        Here’s a roast profile of Guatemala SHB 470gram. A graph at the bottom(light green) represents a rate of rise of BT.

        Though it’s roasted to second crack, I still have a bit of raw bean, grass-like taste and astringency in the cup although the strong chocolate notes are followed.

        If a sensory milestone doesn’t tell me the right or wrongness of the roast progress, why should I pay attention to it, and how can I adequately react(adjusting heat supply or damper) to each stage of sensory milestone?

        Thanks for your help.

        • I looked at your chart and it is a normal roast development curve. You should not get “underdeveloped” taste. Especially that you take it 30 sec into the 2nd crack. I can’t imagine to get grassy notes in a roast like this unless there is something really wrong with coffee or your logging software which I suppose it’s not, because you are getting the color and the cracks. Do you get grassy notes with other coffees too?

          I rarely roast to 2nd crack. Can I ask you what do you compare your coffee with?

          By astringency do you mean acidity? Astringency is stronger as the roast progresses. You get smoky and bitter notes more present.

          I would recommend to invite for tasting some of your coffee colleagues and check what they think.

          • Hi I am using W15 but I have a question on roast profile bottom up / turning point takes about 2 to 3 min for 10kg batch. Is this normal ?

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