Difference between revisions of "Chris Knutson"

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Hop Isomerization Paper

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-{| border=0 style="border-collapse:collapse; width:100%;"
-! bgcolor=lightgrey |Isomerization of Humulus Lupulus α-acids
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-| '''Abstract'''
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-|<!-- Abstract Text Start -->Hops are added to the brew kettle at different times in order to add specific character to the beer. “Early addition” of hops primarily add bitterness; “late addition” of hops add primarily flavor and aroma. Hop bitterness comes from the isomerization of a-acids with effective utilization of not more than 30%. The reason for low utilization is most likely a combination of factors related to both the volatility of the a-acids as well as degradation of the isomerized a-acids. The contribution of “late addition” hops to the final beer is a result of essential oils and is not fully understood. Recipe formulations which have a strong hop component add hops throughout the brewing process as well as after primary fermentation (dry hopping). This poster will present a collection of data that suggest alternative methods of hop processing to both increase the utilization of hop a-acids and better preserve the essential oils in the final product.<!-- Abstract Text Stop -->
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-|'''Introduction'''
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-|Hops (Humulus Lupulus) are a quantitatively minor component in the beer brewing process, but a qualitatively major component of the finished product. For every 1 US gallon (~4 L) of beer, 2 pounds (~ 1 kg) of grain and only 0.4 ounces (~ 10 g) of hops are needed. Beers that strive to highlight the malty character in a beer trend towards the inclusion of more grain, those looking to highlight “hop character” trend towards the inclusion of more hops. While grains have always been a part of the beer recipe, it was not until the middle of the second millennium (~1500 CE) that hops became a commonly used brewing ingredient. Hops, like many spices , were added for flavor, but became common due to their yet to be discovered antibacterial properties. Note that beer in the earlier days was quite different from the modern versions and many needed something to cover up the less desirable characteristics.
-Hops are added during the brewing process to contribute to three main characteristics to the beer: bitterness, flavor, and aroma. To achieve these characteristics, different hop varieties are selected and the hops are added to the boil kettle at different times. Hops added “early” in the 60 minute boil add bitterness; hops added “late” contribute to the flavor and aroma. The chemical species within hops associated with flavor and aroma are generally the essential oils that reside in the Lupulin glands of the hop flower (cone). Hops added early also contain these essential oils; however, these oils are volatized in the boil kettle.5
-It is understood that the bitterness associated with hops added early in the wort boiling process is a product of the isomerization of a-acids within the hop. Non-isomerized a-acids typically have a low solubility; however, once isomerized, a-acids take on a much more soluble, iso-a-acid, form6. (see scheme 1).
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-|'''Motivation'''
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-|Hops can be a major financial investment in a beer. The wholesale price of grains (~$0.50/lb.; $1/kg) is considerably less than the price of hops (~$10/lb.; $20/kg). In the above example hops are ~1% of the recipe but cost ~2000% (x20) more than grain. As above, for every 1 US gallon (~4 L) of beer, $1 of grains and $0.25 of hops are needed. As with most business related activities, increasing the process efficiency is one means of lowering the production costs.
-The main topic of this poster relates to the efficiency of converting a-acids to iso-a-acids. Under standard brewing conditions, an estimate of 30% of the added a-acids are converted into iso-a-acids. This low efficiency is a result of many factors including, the volatility of a-acids, the degradation of iso-a-acids, and the physical dynamics of the brewing process.3,4,5
-We have undertaken a set of experiments to determine if we can pre-isomerize the a-acids in the hop cone prior to the brewing process. Our approach involves the heating of packaged hop material at 100 ⁰C for 1,2,3,4 hours. Analysis of the a and iso-a-acid concentrations is done by HPLC.1,2
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-|'''Methodology'''
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-|Samples of hops were packaged in heat sealable packaging and then heated in an oven at 100 ⁰C for a variable amount of time. Extractions were prepared using approximately 3g portions of hop material in 150 ml of extraction solvent. The extraction solvent was 75% Methanol, 24% deionized H2O, 1% Concentrated HCl. The extractions were mechanically stirred for 1 hour and then filtered through a 0.45 mm filter and introduced to a Supelco Analytical Supelcosil LC-18 25cm 4.6mm, 5mm HPLC column in 10 ml injections. High performance liquid chromatography was conducted at 28 ⁰C with a gradient mobile phase: 65% MeOH 0-12 min, then up to 85% MeOH by 18 min, hold at 85% until 28 min, then back to 65% MeOH at 33 min while monitoring changes in UV absorbance at 270 nm. 1,2
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-|'''Data'''
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-|style="text-indent: 10px;"| Text
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-|'''References'''
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-* ASBC Methods of Analysis. Hops Method 14. Approved 1990. American Society of Brewing Chemists, St. Paul, MN, U.S.A. doi: 10.1094/ASBCMethod-Hops14
-* Danenhower, T. M.; Force, L. J.; Peterson, K. J.; Betts, T. A.; Baker, G. A. HPLC Analysis of a- and b-Acids in Hops. J. Chem. Ed. 2008, 85(7), 954-956.
-* De Keukelleire, D. Fundamentals of Beer and Hop Chemistry. Quimica Nova, 2000, 23(1), 108-112.
-* Kappler, S.; Kral, M.; Geissinger, C.; Becker, T.; Krottenthaler, M. Degradation of Iso-a-Acids During Wort Boiling. J. Inst. Brew. 2010, 116(4), 332-338.
-* Malowicki, M. G. and Shellhammer, T. H. Isomerization and Degradation Kinetics of Hop (Humulus lupulus) Acids in a Model Wort-Boiling System.  J. Ag. Food Chem. 2005, 53, 4434-4439.
-* Urban, J.; Dahlberg, C. J.; Carroll, B. J.; Kaminsky, W. Absolute Configuration of Beer’s Bitter Compounds. Angew. Chem. Int. Ed. 2013, 52, 1553-1555.
-|}
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