Thought I'd share my morning's activities with the forum.
One of the few things I don't measure in my beer is the end colour. Everything else I've got pretty much covered...gravity, temperatures, etc. So I thought I'd have a go at making a photometer which (eventually) should be able to tell me the EBC of my brews.
Here's the theory.
According to wikipedia, EBC is estimated by measuring the absorbance of 430nm light through a 1cm sample of the beer. Standard practice to measure absorbance like this is to split light through a prism to isolate 430 nm, then use photon detectors/multipliers to measure the attenuation of the lightpath through the beer. Riiiight!
So, I recon a suitable alternative to all this is the humble web-cam. My argument is that RGB CCD devices can act as a photon detector, isolated to aorund 430nm by discarding the red and green channels and keeping the blue. This page shows that the blue component of RGB is roughly 440nm. That's close enough to 430 for me! Of course, this will vary from manufacturer to manufacturer, but I'm only really interested in if this is possible at all rather than achieving great accuracy.
All I need to do now is create a light-box of some sort to give a steady source of light, and use a web-cam to record an image of a beer sample. The image can then be programatically broken down into RGB components, and the blue channel can be used to give an estimation of EBC. Et voila!
So here goes...
1) Obtain (old) webcam
2) Take lens & board out of webcam
3) Gather other components for light box.
4) Assemble light source. This is an LED from a torch, with a switch.
5) Cram everything into the box
6) Aaaand we're done
7) Now the software. It doesn't look like much at the moment, but the basics are there. The box on the left is the feed from the webcam.
The graph is showing the intensity of the blue channel (from 0 - 255).
8 ) Ok, it's ready for reading beer samples. Now to see if the photometer can detect differences in beer colour.
Here I've prepared a range of dilutions of Meantime's London Stout. The dilutions are: 0% (water), 10%, 20%, 30%, 50%, 70%, 80%, and 100%.
9) Loading a sample into the photometer
10) Here are the readings from the software. Quite a nice curve, not quite logarithmic, but at least there are no anomolies.
11) I put the data into zunzun.com to get an equation for the curve (simple power curve, it turns out), and add this into the software.
The idea now is that the photometer should be able to tell me what the dilution of a sample chosen at random is. And it bloody works too!
Here it is with the 70% dilution sample.
With all the samples, the predicted dilution is within about +/- 3%. This is as far as I have got up to now.
Next steps will be to obtain beers with known EBC (the Meantime London Stout used here is a known 50 EBC) to get a feel of how the unit reacts to different styles of beer. From there, a calibration curve can be prepared, which will allow direct estimation of the EBC of an unknown beer.
I'm not to au fait on the EBC/SRM calculations at the moment, but I'll have a good read over the week. If anyone has working knowledge of EBC calculation, I'd love to hear your comments/critisim.
Cheers!
