Monday, August 30, 2010

Hop analysis: alpha and beta acids

First of all I want to thank all of you who visit this blog. More than 1000 visits! And of course a special thanks to my follower (you know who you are!), the repeated visitors and my 4 fans on facebook. I'm glad so many beer geeks have found the way to my blog. Now to the subject of today.
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!

Monday, August 9, 2010

How my quadrupel turned into an oud bruin

This week I tasted a bottle of a quadrupel I brewed 2 months ago, and was surprised to discover a slight sourness. Not bad at all, it tasted a bit like Rodenbach, or Oerbier. However, it was not supposed to be there, which makes it an infection. I suppose this is what can happen if you brew during summer. I put a drop of the dregs under the microscope and found it to be a pediococcus infection. Luckily the taste is realy nice, so I won't pour it down the drain. Below a picture of the dregs: