Ask The Brewmasters

Hi all, 

I am looking into optimizing the sample preparation of beer samples to run them through an alcohol meter. For alcohol measurements the sample is required to be very clear. At the moment our procedure is to mix the sample with kieselguhr and filter the mixture through a filter paper. For extra filtration we sometimes use a syringe filter. I would like to know if using a table centrifuge would be a good idea to reduce the amount of work load and plastic waste; which could compensate eventually the extra investment required. Is anyone out there using this method and what would be the recommended rpm to successfully spin down yeast and bacteria (in case of kettle sour beers). .

Any input would be much appreciated!

Cheers!

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Desiré Gandia Fernandez
Quality Manager
Oedipus Brewing
Amsterdam
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Hey Desiré, glad to help. At a previous lab, I used a benchtop centrifuge quite often to clarify samples prior to ABV analysis with an Alcolyzer - you are correct in that accurate and repeatable results requires very clear samples. 

However, it's worth noting that the filtration step is often still necessary to aid in the removal of CO2 entrained within the liquid - even beer that has not yet been carbonated can often have enough dissolved CO2 to cause issues when delivered through a peristaltic pump (which creates a slight vacuum and thus can cause CO2 breakout).

I would recommend a benchtop centrifuge for the initial clarification step, then using a glass fiber filter paper or a paper filter as you see fit to remove additional solids and CO2. Doing this will remove most if not all need for a kieselguhr preparation (in my experience). Low speed and time (if i remember correctly, 2000 RPM for 2 min) is more than sufficient to accomplish this. 

As an aside, a benchtop centrifuge is often useful for other things (cell counting comes to mind) and will definitely be a worthwhile purchase. 

Desiré,

I concur with Theo.  We used it in our lab for over four years and typically centrifuged the sample and then filtered with kieselguhr in a paper cone.  We also made sure the sample was consistently de-carbonated.  This is where most measurement consistencies come from in repeating samples.  We have used the Alex500 for quite a while with great and consistent results.  The only real consistency issues we had was when we got samples down under 0.8% ABV (such as with NA beers), then accuracy and consistency both suffered.  However, despite going a little bit out of the upper range, we found the accuracy and repeatability to be great up to almost 18% ABV for our seltzer base fermentation readings.

I checked with Anton Paar and the Alex500 is still available and has not been taken off the market.  We worked with a few university labs and a couple of big breweries over the years and the most valuable feedback we got from everyone is that sample preparation is critical to consistent results with fermented and unfiltered beer for accurately measuring ABV.  You might want to consider using an ultrasonic bath to help de-carbonate samples as well.

Good luck!

Glen Sprouse

Brewery Development & Automation, LLC

678-778-0212

Thanks a lot for sharing your expertise! Indeed we know the limitations of using it with beers under 0,5% Abv. In Europe at least the Alex500 is still available. Cheers!