P1253037245AfOiR

1
Extraction and isomerization rates of a-acids
for bittering beer
Cindy Spangler and Dr. Paul Hooker Department of
Chemistry, Westminster College, Salt Lake City,
Utah 84105
Results continued
Introduction
Method
Results
Columbian pellet hops (14.1 alpha acids) were
purchased from a local brewing shop. Ten
separate beakers were filled with equal amounts
of water and equal quantities of hops were added
to the boiling water. In intervals of 5 to 10
minutes, samples were collected. Figure 1 shows
the process of analysis conducted.
For over 400 years hops have been added to beer
in order to impart a distinctive bitterness that
complements the sweetness of the malt, to act as
a preservative, and to provide a flowery, herbal,
or citrus aroma. The final bitterness of a brew,
often the defining feature of a particular beer
style, is determined by the quantity of a- acids
extracted during a protracted boil of the wort.
Alpha acids are organic compounds found in
relatively high concentrations in the glands of
the hop cones, humulus lupulus. The bittering
capacity of a particular hop is usually quoted as
an alpha acid percentage, whereas the bitterness
of the beer is quoted as the iso-alpha acid
content, as the alpha acids undergo an
isomerization reaction during the boil.
In this study, the rate of
extraction of alpha acids and their subsequent
isomerization has been investigated. Our goal is
to determine what other factors influence this
crucial process, such as wort gravity, and
initial alpha acid content of the hops.
HPLC Chromatographs for Iso-alpha Acids
5 minute boil
30 minute boil
Graphs of isomerization rates (top) and alpha
acid extraction (bottom)
Conclusion
The concentration of alpha acids and iso-alpha
acids does show an inversely proportional trend
through the boil however the results do not
demonstrate the consistency need in order to
investigate other factors affecting the
extraction and isomerization rates of alpha
acids. Therefore, we must simplify the
experiment by using the iso-alpha standard to
find the percent recovery from extraction and to
see how iso-alpha acids degrade in solution. We
will be able to make any alterations necessary in
order to get consistent results. After our
procedure has been corrected and verified, we
will analyze the affects of gravity and hops
alpha acid content.
50 minute boil
HPLC Chromatographs for Alpha Acids
Procedures used to extract alpha acids from hops
and iso-alpha acids from wort.
Columbian hops
International calibration standards for HPLC
analysis of isomerized a-acids were obtained from
the American Society of Brewing Chemists (ASBC).
Alpha acid calibration standards were obtained
from the European Brewing Convention. All
standards were prepared using the procedures
provided by the manufacturer. Samples were
filtered and ran on a Buck Scientific BLC-20
isocratic liquid chromagraphic machine with a 20
µL injection loop using an EC 250/4 Nucleosil
100-5 C18 Hop column. Adsorption was measured at
254 nm for alpha acids and 325 nm for iso-alpha
acids.
Acknowledgements
De Keukeleire, Denis. Fundamentals of beer and
hop chemistry. Quimica Nova, 23(1) (2000)
108-112. Keukeleire, J., Ooms, G., and Heyerick,
A. Formation and Accumulation of alpha-acids,
beta-acids, desmethylxanthohumol, and Xanthohumol
during Flowering of Hops. J. Agri. Food Chem.
2003 Jun 1851, 4436-41. Malowicki, M. and
Shellhammer, T. Isomerization and degradation
kinetics of hop (Humulus lupulus) acids in a
model wort-boiling system. J. Agric. Food Chem.
2005 Jun 153(11)4434-9. Moir, Michael.
Hops-A Millennium Review. J. Am. Soc. Brew.
Chem.I 58(4)131-146, 2000
20 minute boil
Clockwise Leaf hops, pellet hops, and plugs
Fresh hop cones on plant
50 minute boil