Winter 2008 Newsletter

What's in Your Holiday Brew

During the winter holiday season, many breweries introduce specialty beers that are only available once a year and are in limited supply. These hearty holiday brews are rich and malty, often with hints of spice or nuts. Additionally, these winter beers emanate intense, biting aromas, sometimes sweet and inviting, sometimes bitter and poignant.

We wanted to know what aromas make a holiday brew different from a lighter, “summer” variety. Furthermore, what compounds are present in one holiday specialty and not in another? One way to answer these questions is by use of Gas Chromatography/Mass Spectrometry (GC/MS) utilizing Solid Phase Microextraction (SPME).

Background

While we all know that fermentation of sugar by yeast produces alcohol, it is less well known that the aromatic “bouquet” of a well-made beer is actually derived from biochemical reactions caused by yeast.¹ Some strains of yeast may produce a darker, richer beer (generally referred to as ales), whereas other strains might produce lighter, sharper beer (generally referred to as lagers). Regardless of the type, a beer’s aroma is caused by numerous compounds. It has been reported that some beers contain over 560 aromatic compounds contributing to the overall aroma.² Table 1 shows some common compounds associated with the aroma in beer.

Table 1: Common Compounds Associated with the Aroma in Beer^3,4

Compound Name	Aroma
Ethyl Hexanoate	Apple
Ethyl Octanoate	Fruity
2-phenyl ethanol	Honey
Ethyl Acetate	Ethereal
Isoamyl Acetate	Banana
Isoamy Alcohol	Spice

Samples

We obtained nine different brands of beer from various stores around St. Louis. Of the nine samples, eight were holiday ales and one was a lager (used as a control). Table 2 lists the region and country of origin of the sampled beers as well as a description of their flavor.

Table 2: List of Analyzed Beer

Sample #	Beer Type/Designation	Manufacturer	Flavor Description
Control	American Lager	Anon.	Malty
Ale 1	Very Bad Elf	Ridgeway Brewing	Fruity, Spices
Ale 2	Nut Cracker Ale	Boulevard Brewing Co.	Rich, Nutty
Ale 3	Christmas Ale	Anchor Brewing Co.	Caramel, Blueberry
Ale 4	Schlafly Christmas Ale	Schlafly Beer	Earthy, Woody, Cloves
Ale 5	Santa’s Private Reserve	Rogue Ales Brewery/ Brewer’s on the Bay	Hops, Lemongrass
Ale 6	Celebration Ale	Sierra Nevada	Fruity, Citrus, Bitter
Ale 7	Fireside Nut Brown	Leinenkugel’s	Caramel, Roasted Nuts

Analysis

Following preparation, the samples were tested by GC-MS using solid phase microextraction (SPME). SPME utilizes a silica fiber that has been coated with a polymeric or solid adsorbent. When the adsorbent is exposed to the sample headspace, the volatile compounds become adhered to the surface of the fiber. After a set exposure time, the fiber is withdrawn and inserted into a GC injector port, at which point the volatile components become desorbed.

After thermal desorption in the injector housing, the compounds enter the GC column that is often an open tubular capillary column with an inner coating of a stationary phase. The column technology is precisely designed to control the chemical properties of the stationary phase and minimize active sites from the glass. Components within the column migrate by use of a carrier gas (e.g., helium) and appropriate thermal conditions while separation occurs by exploiting a difference in the volatility and polarity of the components.

Once the compounds pass through the column, they are analyzed with a mass spectrometer. In mass spectrometry, the resolved sample components are ionized and separated in a mass analyzer. The fragmentation pattern of a sample component and its computer library match enables sample identification.

Results

The results of the experiment can be found below. All but one compound found in the control lager was found in the winter ales, albeit in varying concentrations. Table 3 shows these compounds along with their specific aroma. All beers sampled contained the compounds listed; however, the differences in the concentrations and proportions of these compounds in each beer contribute to the specific “bouquet” of the beer.

Table 3: Compounds in All Beer Samples^3,4,5,6

Compound	Aroma
Ethyl Acetate	Ethereal
Isoamyl Acetate	Banana
Isoamyl Alcohol	Spicy
Ethyl Hexanoate	Apple
Linalool	Flower, Lavender
Phenethyl Acetate	Rose, Honey, Tobacco
Phenylethyl Alcohol	Honey
Octanoic Acid	Cheese, Sweet
Ethyl Octanoate	Fruity

Tables 4-10 shows some of the compounds specific to the holiday ales. The aromas range from descriptions of musty to mandarin and from spicy to smoky. Ales 2 and 4 contained the most aromatic compounds in this experiment, while Ales 6 and 7 contained the least.

Table 4: Compounds Found in Ale 1 (Very Bad Elf)^4,5,6

Compound	Aroma
2-Butylfuran	Spicy
Diethyl Succinate	Wine, Fruity
Ethyl 9-Decenoate	Fruity
α-Pinene	Minty

Table 5: Compounds Found in Ale 2 (Nut Cracker Ale)^4,5,6

Compound	Aroma
Ethyl 9-Decenoate	Fruity
β-Pinene	Herbal, Pine
Hexanoic Acid	Sweet
4-Vinyl Guaiacol	Clove, Curry, Woody, Smoky
Farnesol	Floral
Lauric Acid	Metallic
2-Ethylhexanol	Rose, Green

Table 6: Compounds Found in Ale 3 (Christmas Ale)^4,5,6

Compound	Aroma
Furfural	Almonds
(4S)-(-)-Terpinen-4-ol	Musty, Dusty, Earthy
Methyl Isoeugenol	Spicy, clove, Carnation, Woody
Myristicin	Spice, Warm, Balsamic
Diethyl Succinate	Wine, Fruity

Table 7: Compounds Found in Ale 4 (Schlafly Christmas Ale)^4,5,6

Compound	Aroma
Isobutyl Isobutyrate	Fruity
Propanol	Alcoholic
Butanol	Medicine, Fruit
Octanol	Waxy
Eugenol	Clove, Honey
Caryophyllene oxide	Herb, Sweet, Spice
β-Pinene	Herbal

Table 8: Compounds Found in Ale 5 (Santa’s Private Reserve)^4,5,6

Compound	Aroma
Myrcene	Peppery, Spicy
2-Methylfuran	Chocolate
2-Undecanol	Mandarin
Butyl Isobutyrate	Fruity

Table 9: Compounds Found in Ale 6 (Celebration Ale)^4,5,6

Compound	Aroma
β-Pinene	Herbal
2-Methylfuran	Chocolate
Perillene	Woody

Table 10: Compounds Found in Ale 7 (Fireside Nut Brown)^4,5,6

Compound	Aroma
2-Ethylhexanol	Rose, Green
Ethyl 9-Decenoate	Fruity

Conclusion

While the unique aromatic compounds of the holiday ales may not always correspond with their flavor, they compliment to the overall “bouquet” of the ale, enhancing the holiday experience. Chemir toasts the creativity of these craft brewers in their selection of interesting compounds and ingredients. We admire their ingenuity as they capture the spirit of the season in their winter holiday beers. This winter, perhaps you will stop and enjoy the aroma the next time you sip your favorite holiday brew.

Sources:

1) Nykänen, L.;, Suomalainen, H.; Aroma of Beer, Wine and Distilled Alcoholic Beverages, Edition 1: Springer: New York, NY, 1983: 3-4.

2) Maarse, H.; Volatile Compounds in Foods and Beverages, CRC Press: New York, NY, 1991: 30.

3) Ivusic, F.; Gjeldum, M.S.; Nemet, Z.; Gracin, L.; Maric, V. Aluminum and Aroma Compound Concentration in Beer During Storage at Different Temperatures. Food, Technol. Biotechnol. 2006, 44, 499-505.

4) Acree,T.; Arn, H. Flavornet and Human Odor Space. http://www.flavornet.org/ (accessed DEC 08).

5) Luebke, W.; The Good Scents Company. http://www.thegoodscentscompany.com/ (accessed DEC 08)

6) Leffingwell, J.C. Chirality & Odour Perception. http://www.leffingwell.com/ (accessed DEC 08)