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Roast Color Nerdy Stuff


HarryDog wrote:

How big is the site glass on the roaster? How hot does the glass get?

What about the +200C degrees of the glass ? Shock


oldgrumpus wrote:

A laser color analyzer that looks through the site glass...

I am pretty sure what you see there is an IR measurement device, and laser is used only as a pointer.
They may claim they are measuring color, but actually they are measuring an IR radiation, which is the same as the "trier in the pipe" project above.
I was concerned about the glass thickness and temp, for temp I might cut a ring out of a silicone baking mat and stick it on the bottom, you would just touch it to the glass for a moment to push the button. Might effect the white calibration tile?

or You just pull a few beans put them in a small shallow container and take the reading. I'm going to order one up and see what I can do with it. I don't have a site glass but could fill a small glass milk jug with beans and rotate it to see how the glass and rotation effect the reading compared to stationary beans without a glass barrier?

Who has those coffee bean color cards on the web?
Sweet Marias has something, will look around.
HarryDog, Yes, cards at Sweetmarias, others are out there too. You might want to see Sweetmaria’s video on their cards too.

Also Testrite has cards. More $ though…


renatoa wrote:

They may claim they are measuring color, but actually they are measuring an IR radiation, which is the same as the "trier in the pipe" project above.

That’s a very interesting possibility. Worth exploring. I know from experience that some types of glass filter out IR but maybe the borosilicate glass commonly used for site glass doesn’t. Or maybe it’s just not a factor?

The “trier in the pipe” measures IR wavelengths in 5 separate frequencies. I don’t know enough about the subject, but that must be different than measuring heat with an IR thermometer?
So I ordered the Pro version as it is slightly better $125 cad,
I did find two others that might be of interest.
Pro Version




HarryDog wrote:

So I ordered the Pro version as it is slightly better $125 cad

Excellent! Please keep us up to date!!
Clever Coffee Dripper
Grinder: Macap M4
Roaster: Completed drum roaster project photos shown here:
Videos https://www.youtu...Bd1NrdpSUH
Hello Everyone, I'm looking for the paper that has the CIELAB readouts corresponding to the Agtron roast levels. Tom from Sweet Marias eluded to it in his video, wondering if anyone has seen it?

Actually you can build your own roast level chart, based on your taste.
The more important is that you have a reproducible way to measure, and establish some references, not the value of references.
Is like the roasting, is not important that you have FC at 195 or 205 degrees, what matters is the speed you arrived there, and how you drive the roast from that point forward.
I agree, if it works I will be able to sample and create results that can be used. I was wanting to compare to the standard readings made by Agtron and get my hands on one of the cards just to read/test them. I don't live in the US so it's maybe Taiwan to get a card, Sweet Marias won't sell the card by itself. More hassle and cost then the cost of the meter?
This white paper could give an idea of the degree of... nerdiness... Shock
Thank you renatoa, I read an article from Hunter labs testing at 640nm before but not at 880nm wave length, I think the first meter is a unit that Hunterlab uses or sells? The second I don't know.

The meter I ordered has a range or 400-700nm should be an ok test device. Not sure if I can set that wave length or how it works.
Thanks again.

Why is this equation R² = 0.9715 on the graph and what is the relation to the data on the USPRO graph?
I guess it's part of the calculation of the Agtron value.
Edited by HarryDog on 02/04/2023 10:55 PM


R-Squared (R² or the coefficient of determination) is a statistical measure in a regression model that determines the proportion of variance in the dependent variable that can be explained by the independent variable. In other words, r-squared shows how well the data fit the regression model (the goodness of fit)

In our case, the 0.97 value of R², means a very close fit to a proportional (linear) relation between the two wavelengths used for tests, shown also on the graph.
All data tell us that using any wavelength to evaluate of Agtron will led to an acceptable error, in the 3% ballpark.

Nerd enough ? Grin
Edited by renatoa on 02/08/2023 1:32 AM
I think I get the general idea, Thanks.


renatoa wrote:

Nerd enough ? Grin

NO! Just kidding!! I didn't think this thread would go "over the top" but my expectations were too low. Amazing indeed.

All joking aside, I'm learning way ABOVE what I expected to... and that's a very good thing!
Clever Coffee Dripper
Grinder: Macap M4
Roaster: Completed drum roaster project photos shown here:
Videos https://www.youtu...Bd1NrdpSUH
So the Pro Colormeter came in and I have been doing some testing.
The test with the milk bottle forget that as it was a fail, the bottom glass is raised and has some texture on it and was no good.
I did find a glass with a flat bottom and these tests were fairly consistent. The reading inside the glass was about 40% the actual reading of the bean but it was consistent in the tests.

Reading Whole Beans, this was an issue if attempting to read a tray of beans from a roast, the reading varied an easy 2 points.
Now reading the round back of the whole bean was very close each time. I tested 10 random beans from a roast and was surprised they were so close. I have not tested ground beans yet.

I want to get my hands on a RoastRite card but no luck yet, don't really want the individual cards at 100USD + Shipping + Tax or Vat as that's crazy. Looking for one in North America that is not 2x the price of the meter. I only found one place that had stock and the price was ok but shipping was stupid. Most shops won't sell the card by itself either, shipping/importing the beans is a bit high.

I did get one card with beans in a kit and read that for fun, how accurate I don't know but this file is what the meter read next the the Roast name and then the color the app came up with and the true readings from Google.

Looks like PDF's are not allowed, loaded pictures!
HarryDog attached the following images:
chart3.jpg chart2.jpg chart1a.jpg

Edited by HarryDog on 02/18/2023 11:11 AM


HarryDog wrote:
...and the true readings from Google.

I think I understand most of your post but not sure what this means or how you confirmed from Google.
The app will provide a color to match the read of the card or coffee, I was using the CIElab color space, I then used the reading of the point in the color space that is represented by the color the app thinks it is and confirm with a Google search.

So for Blonde the meter reads this.
Blonde #725239 L=37.64 a=10.41 b=19.91
Google tells me #725239 is this
CIE-lab L=37.6757 a=10.0296 b=19.8914

So this looks like a close read but I don't know the value of the original card.
So the info the Meter and app is giving me can be confirmed with the Google search.

I can't tell you how accurate this is as I don't know the original card color space reading?

For what it's worth the info from the meter and app look to be confirmed by the info on the Color Hex site. When I visually compare the color it looks the same as the card.

I think the Meter and app would be a good tool to identify roast level on a budget. During a roast you would need to pull a bean to get a good read.

Hope I'm clearer with this as I'm no expert on color space but have played with some of this years ago.
Just did a roast.
#4e3d35 L=27.38 a=5.82 b=7.62 401.5 F (Full City) according to the chart.
HarryDog attached the following image:
If would be mine, according to graph, this would be medium roast.
Is the color really relevant? ... not enough to read the darkness only ?
How many hues could have a "coffee brown" to change the judgment, compared to a monochrome image ?
In colorimetry, brown is an mix of red and green. The coffee brown seems to be an equal balance of the both, I am unable to see any red or green hue in a coffee bean roasted of any degree. Many decades photographer eye...

The guy from Roast Vision sell for 300 his device made using a $5 pulse oximetry sensor, able to distinguish only 36 levels of gray... not even fifty Grin
And SCA quote him as innovative... Shock
Edited by renatoa on 02/20/2023 6:29 AM


renatoa wrote:

If would be mine, according to graph, this would be medium roast.

The Color chart I have, I have no idea how accurate it is but putting the beans on the card they are Full City to Dark.
The Chew taste test dark!

Now the artisan log shows my temps and I think they are low, using my guess at temps Medium?

Using the meter? Because they are positive numbers.

L= lightness
a= (red-green) or redness
b= (yellow-blue) or yellowness

So using the meter reads of the chart I have, the only one I have.

L- 27.38 (How light or dark) puts it at Full City
a=5.82 (How Red) puts it between Full City and Full City+
b=7.62 (How Yellow) puts it between Full City and Full City+

How relevant is the color? I don't know but visually using the chart I put the beans in between Full City and Full city + and I think the meter reading backs that up. Based on eating a bean (Blindfolded) I would say it was a Dark roast.

I'm sure some beans will present darker or lighter then others and the Sumatra is a darker earthier tasting bean?

Do you think I went wrong with comparing the bean to my created color chart?
I’ve been keeping an eye on progress with this thread. Very interesting indeed. Within the visible spectrum Renatoa is spot on with the red green thing, it’s often used in agriculture for detecting ripeness of fruit and veg although not so good for brown.

From a little research it seems the best data might be found in the NIR range so I’ve ordered some bits to make a cheap colour spectrometer. There’s a chap on YouTube with instructions and code on GITHUB.

There are also some nice cheap, visible and NIR spectrum sensors on Sparkfun - plenty to ‘waste time’ on.


HarryDog wrote:

Do you think I went wrong with comparing the bean to my created color chart?

No idea, especially on the chew test...
For my roast I am using mainly the weight loss to judge their roast level, regardless of any color and taste.
But weight loss judgment is valid only if related to greens humidity, else...
If you want an evaluation during roast, then color seems the way to go. For me is development time.
With my current roaster it's not so easy to check the beans during the roast so just checking after as one more data point.

Weight loss is 16.98%, so the sweet maria chart puts this at Burnt?
Other sites put this at high end of Medium.

What are some trusted numbers for roast levels based on temp and or weight loss? A site I should consider correct values to use as guidelines?
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