A Hoppy Little Story

Now that we’re getting into the warmer months of the year, you’re probably starting to see pop-up beer gardens or people outside relaxing with a nice cold one. Since the beer industry has been evolving and people are enjoying craft beers more and more, there are tons of unique brews on the market. If you are not a beer connoisseur, then you may not know what gives your favorite India pale ale or summer lager its intriguing characteristics. The ingredient responsible for the bitterness and much of the aroma are the hops. There are an incredible number of different hop varieties and every single variety has its own personal profile! Some common U.S. hop varieties include Cascade, Centennial, Citra, and Nugget. But, you may be asking yourself, “what makes these hop varieties so different?” TERPENES! Terpenes are a class of organic compounds that are comprised of isoprene units and they are what give hops their unique aroma and flavor profiles. There are many different classes of terpenes, but the classes that we are interested in are the mono- and sesquiterpenes, which include limonene, humulene, pinene, myrcene, to name a few.

http://www.chemspider.com/Chemical-Structure.20939.html

Limonene – http://www.chemspider.com/Chemical-Structure.20939.html

Since I have an interest in quality craft beers, I wanted to dive into a variety and look for some terpenes. Luckily for me, a friend of mine in Restek’s reference standard department grows his own hops. Thanks, Joe! When these hops were harvested last year, Joe vacuum packed me his finest Hallertau variety.

Ground Hops

The hops were added to a Blixer processor with dry ice and then ground into a very fine powder. 0.5 g of the hop powder was measured into a 50 mL QuEChERS tube (cat# 25846), followed by 10 mL of isopropanol. The mixture was vortexed for 5 seconds, then sonicated for 5 minutes, repeated three times. 1 mL of the supernatant was filtered using a 13 mm, 0.22 µm, PTFE syringe filter (cat# 26142) and added to a 20 mL headspace (HS) vial (cat# 24685). 19 mL of RO water was then added to the 20 mL HS vial, which was then capped and ready for analysis. Further sample preparation included the CTC PAL RTC rail system, where samples were analyzed via solid phase microextraction (SPME), using direct immersion (DI), with gas chromatography-mass spectrometry. A divinylbenzene (DVB) SPME-Arrow (cat# 27486) was used for this SPME Arrow-DI-GC-MS method.

 

 

 

 

Total Ion Chromatogram of Terpenes in Hops

 

Using Restek’s Terpene Mix 1 & 2 (cat# 34095 & 34096), we were setup to identify 23 different terpenes. After normalizing the responses for terpenes to 100% we were able to gather a nice breakdown of the terpene profile for Joe’s Hallertau. Using the NIST mass spectral database, we were also able to identify several other terpenes (i.e. beta-Phellandrene), but these were not added to the pie chart.

 

 

So, the next time you’re enjoying a cold one on a hot summer day, give it a good sniff to get an idea of what terpenes may be in there. Every beer has its own unique hoppy little story to tell! Cheers!

 

Photo courtesy of Wil Stewart

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