Can you explain the numbering of roast color scales?

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
SJM
Posts: 1819
Joined: 17 years ago

#1: Post by SJM »

I love my Tonino !!!!

But I have to admit to having a hard time getting my mind to accept that higher numbers are lighter roasts.
Can someone explain the reasoning for this?

I think if I could grasp that then I would have an easier time figuring out why a Tonino 100 is lighter and better for brew while a Tonino 80-90 is darker and better as an espresso. (Take those numbers as symbolic and not as absolutes, please). Since we go through the lighter phases on the way to the darker ones, it would seem more logical (to me) for the numbers to go upwards towards darkness.

Susan

Marcelnl
Posts: 3831
Joined: 10 years ago

#2: Post by Marcelnl »

Is it reflectivity that is measured?
LMWDP #483

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JojoS
Posts: 170
Joined: 11 years ago

#3: Post by JojoS »

Darker means less light reflected back to the sensor good enough explanation? Agtron numbers flow the same way.

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MaKoMo
Posts: 846
Joined: 16 years ago

#4: Post by MaKoMo »

Indeed, the Tonino measures reflectivity. As the Tonino is open-hardware all designed (incl. firmware) are public anyhow, I can give even a little more details. The Tonino measures the light reflected from the subject (the tamped coffee surface) using its 64-channel true color sensor. Those channels are divided in 4 groups. The elements of three of those groups are dotted with small filters to select a certain frequency spectrum corresponding to the colours red, green and blue. The current Tonino firmware uses only two of those groups, namely the blue and the red one. Coffee reflects light mostly in the red and near infra-red frequency space. Both of those are measured via the "red" group as the sensor is operated without an IR filter. We discovered during the development of the Tonino, that the ratio between blue and red, so the red shift of the reflected light, most closely follows the roast degree. Therefore this ratio is computed by the Tonino's firmware and mapped via the selected scaling to values displayed on its screen. The default Tonino scale maps the values from 0 to 250 in a linear way. However, nothing stops you from defining a (or simulate an existing) scale that does an inverse mapping from 250 to 0 (inverse like the ColorTrack scale), and/or a quadratic or cubic scale. The open-source Tonino app is the tool to develop such scales for the Tonino.

See our Tonino App quick start guide for further details:
https://github.com/myTonino/Tonino-App/ ... ckStart.md