All The Light We Cannot See
Over the weekend, I got a chance to play with my new toy: a Milton Roy Spectronic 21UVD spectrophotometer. It has the ability to use both the visible (SRM test) and ultra violet spectrum (IBU test), but yesterday I used only visible light to measure the color of beer. In order to do this, I had to measure the absorbance of light at a wavelength of 430 nanometers (nm) as it passed through a 1cm quartz curvette containing my sample of decarbonated beer. The unit of measurement used in the United States for beer color is SRM, or standard reference method. The calculation for SRM is as follows:
SRM = 12.7 x D x A430
^where D is the dilution factor (D = 1 for no dilution, D = 2 for 1:1 dilution) and A430 is the absorbance at 430nm in 1cm path length. A sample deionized water dilution is necessary for some spectrophotometers when the beer or wort is larger than ~30 SRM due to their log linear limit.
I tested my IPA (not diluted), Gose (not diluted), and my Dry Stout (diluted) and came within one to two SRM units of my calculated value. I would have liked my measured value to equal the calculated, but when dealing with used equipment from the 70s, I thought the results weren't half bad. As a comparison, I also tested a Union Jack, which has a published value of 8 SRM on their website. My measured value ended up being 9.9. As you can see, the unit is not the most accurate piece of equipment, but it will be nice to use to try to measure consistency across batches. Going forward, I'll take several measurements, hoping to hit the same value each time.
I'm excited about being able to measure IBUs, but I'm still missing a few pieces of lab equipment. If anyone knows of a cheap centrifuge that can hold 50ml tubes, let me know!