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Calling all QC Techs

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  • Calling all QC Techs

    Ok, so here's the deal.

    I'm a biochemistry student who is now a lab technician at a microbrewery, replacing a person who has absolutely no experience or schooling in the field. As a BIC student, I also have no brewing background, but definately have the micro and chemistry to back up what I don't know, as well as the fact that I worked at the Beer Store for a number of years.

    Since the tech before didn't know why a lot of tests are done, I too also struggle with this understanding, although many I have been able to reason out. My main question concerns the IBU's of beer and how to actually calculate them.

    The procedure we use is simple; 5 mL of the beer being tested, 10 mL of iso-octane and 0.5 mL HCl, and it's shaken for about 2 minutes. The top layer is then removed and placed into the spectrophotometer at 275nm in a quartz cuvette, and then the absorbance reading is multiplied by 50 to obtain the IBU reading.

    I struggle with having numbers from anywhere between 8-35 IBU, even on the same brews, which makes me wonder about the method. If I shake too hard or for too long, the IBU's go up; too soft or too short, and they go down.

    I've tried to find answer in literature, but most I have found require resources we can't afford, or don't give good answers. I've contacted professors, but since they don't have brewing background, it's hard for them to fully understand.

    Am I doing this right? Can someone help me? Even a simple "keep doing what you're doing" would suffice!

    Cheers in good beers!
    -Nikki

  • #2
    Call White Labs and see if they can assist you in the measurement technique that they use.

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    • #3
      my honest suggestion is that you should get a copy of ANALYTICA-EBC. It's not that expensive, and if your brewery is serious about QC-- get it!


      According to EBC method 9.8:

      10 ml of degassed beer to 35 ml centrifuge tube, add 0.5 ml HCl (6M), then 20 ml iso-octane and 2~3 glass beads.
      Cap the centrifuge tube, shake 15 min on rotary shaker at 130 rpm. Centrifuge for 3 min at 3000rpm.
      Measure absorbance of the iso-octane in 10 mm cuvette at 275 nm using pure iso-octane as reference.
      BU = 50 * A(275)


      "If I shake too hard or for too long, the IBU's go up; too soft or too short, and they go down."
      The key in ANY scientific method is CONSISTENCY! do everything in the same manner, you can always worry about calibration afterward.

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      • #4
        Originally posted by bndionne
        The procedure we use is simple; 5 mL of the beer being tested, 10 mL of iso-octane and 0.5 mL HCl, and it's shaken for about 2 minutes. The top layer is then removed and placed into the spectrophotometer at 275nm in a quartz cuvette, and then the absorbance reading is multiplied by 50 to obtain the IBU reading.

        For the most part, this is the correct method of doing it (with volumes reduced by half of "normal") other than the shaking method. What most breweries and labs use are called "wrist-action shakers" often made by Burrell. These allow uniform and consistent shaking "parameters" (swing amplitude, frequency, distance from axis, etc) as well as multiple samples simultaneously. ASBC-Methods of Analysis says to shake for 15 minutes - obviously out of the question when shaking by hand. I have read journal articles which postulated that shaking by hand for even less than a minute can give you results close to a mechanical shaker, but in my personal experiences (thousands of BU assays) I have found that not to be the case.


        Originally posted by bndionne
        I struggle with having numbers from anywhere between 8-35 IBU, even on the same brews, which makes me wonder about the method. If I shake too hard or for too long, the IBU's go up; too soft or too short, and they go down.
        The reason the BU's go up when you shake harder is you are creating more emulsion which decreases the available organic solvent (iso-octane) for the analytes to be held in, thus increasing their concentration. They also go up when you shake longer because it allows more time for the analytes to be transferred into the organic phase. For this same reason they go down when you don't shake very long, but they also go down when you don't shake very hard because you are not disturbing the aqueous-organic interface enough to transfer all the analytes over.


        If the BU results are important to you, then I would suggest finding a wrist-action shaker. You should be able to find one fairly cheap on a used scientific website or auction site. If that is not feasible and you have to keep shaking by hand, I would recommend consistency. Try to shake each vial in the same way for at least two minutes. The more you can shake at the same time the better, because you know they will have been shook the same way.

        It *may* also help to introduce some sort of plastic beads into the vials which might help disturb the aqueous-organic interface during shaking, leading to more efficient transfer.

        Oh, and if you aren't using polycarbonate centrifuge tubes yet, I would highly recommend getting some. They won't break when they come flying out of your hand during all that shaking.


        Good luck, and don't worry too much: the IBU assay is notoriously imprecise!

        Ian, Redhook
        Last edited by Ian.McL; 06-12-2007, 05:41 PM.

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