We recently bought some hops from a wholesale retailer in Belgium to sell to the members of our homebrew club. Unfortunately the retailer is not the best communicator. First it took several months for him to send the order, then he didn't inform us about the alpha acid content of the hops. He didn't even reply to my mail. It looks like we have to find another retailer next time... Fortunately, I work in a research lab and have access to a spectrophotometer. So I did it myself!
The method for determining alpha and beta acids in hops I found here. As this might be interesting for some of you, I took some photos.
First I pulverized the pellets with a pestle in a mortar. Whole pellets are to dense and would never allow the acids to be extracted from the hops.
For extraction of the oil containing alpha and beta acids toluene is used. After some time looking I found it in a paint store where it is sold a a paint thinner.
After weighing in the hops, I added the toluene and extracted the oils for 30 minutes.
After diluting the samples and control i methanol I read the absorbances at 275 nm, 325nm and 375 nm. Because I wanted to get an idea of the background absorbance by the solvents, I also run a scan of the control. As you can see, down to 275 nm the background is rather low, but at lower wavelengths the absorbance quickly increases.
Finally I did the math and found the Saaz and Styrian goldings to have about 2% AA. The Magnum and Northern brewer about 11%. I guess I'll have to do a test brew to find out if it fits. One more reason to brew!
