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Alcohol Content Diacetyl Levels

Alcohol content, or strength of the beer, is expressed as a The differences assume the conversion of sugars to alcohol by Diacetyl (2,3-butanedione) and 2,3-pentanedione are in a class 8-14 days. Assuming an average of 12 days, the brewer could
percentage, usually in terms of volume of ethanol divided by the yeast. However, it should be noted that fermented beers of compounds called vicinal diketones (VDKs). One of the increase production by 10% a year by cutting the hold time in
volume of beer. In many countries, ethanol concentration is contain some residual sugars, so the alcohol content is biggest returns on investment (ROI) for instrument purchase the fermentation tank by one day per batch. According to the
required to be on the label by law. For example, in the U.S., the estimated. consideration is how long the fermentation tanks are holding European Brewery Convention (EBC), analysis is performed with
reported values must we within +/- 0.3% absolute of the true Shimadzu’s solution to measuring ethanol content is by gas product before the brewing process is complete. This is checked a headspace GC with an ECD detector.
value. chromatography (GC) with flame ionization detection (FID). The by measuring the VDKs. Note – The same GC-2014 with the addition of a FID detector
An accurate way to measure percent ethanol concentration in measurement can be performed according to AOAC Official The VDKs give a buttery flavor, which is generally unwanted can be used for analysis of alcohol content described in “Section
beer is by measuring the specific gravity of the distillate Methods of Analysis 984.14 as well as by the American Society and a marker that the fermentation process is not complete. 2: Alcohol Content,” page 8.
volumetrically or gravimetrically; however, some consider this of Brewing Chemists (ASBC) as Beer-4D. The GC separates the Using a liquid yeast, the primary fermentation process can take
method to waste beer, energy and, most importantly, time. A ethanol from all other components in the beer so there are no
less accurate but easier method is to measure the specific interferences. Also, n-propanol is added to the beer and used as
gravities of the unfermented wort and fermented beer. The an internal standard during the analysis. The method injects
sugars in the unfermented wort raise the specific gravity as two microliters of sample into the GC, and accurate analysis is
compared to water, while the alcohol lowers the specific gravity. completed in a couple minutes as shown below. Peaks
1 Diacetyl 3
2 2,3-Pentanedione
3 2,3-Hexanedione
(internal standard)

1 (7ppb) 2 (3ppb)

7.0 8.0 9.0 10.0 11.0 12.0 min Shimadzu Nexis GC-2030 or GC-2014 with HS-10 Headspace
DETECTOR RESPONSE ETHANOL N-PROPANOL Autosampler for analysis of vicinal diketones
Vicinal diketones (VDK) in beer by Headspace GC

O O

START

0 1 2 3
MINUTES
O O
Shimadzu GC-2014 for measurement of alcohol content Typical gas chromatogram for ethanol in beer with peak height
response compared with that of n-propanol internal standard* Diacetyl (2,3-butanedione) 2,3-pentanedione

A GC-2010 Plus or GC-2014 with the addition of a headspace autosampler can be used for analysis of diacetyl, as described in
“Section 2: Diacetyl Levels,” page 9.

* From ASBC Beer-4D. Ethanol Determined by Gas Chromatography (GC) * Shimadzu brochure: ECD-2010 Exceed, C180-E080, Page 6

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