Transcript Beer Foam: From Head to Toe - John Stephenson

Beer Foam Stability:
From Head to Toe
John Stephenson
November 25, 2003
Prepared for Simon Hesp
Chem 348
What is beer?
 Barley
 Steeped
in water to germinate
 Starches converted to sugars
 Dried
 Hops
 Bitter
flavor, aromatic scent
 Yeast
 Converts
sugars to alcohol
What is foam?
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Foam is a continuous liquid phase that
entraps gas
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Formed by two methods:
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Dispersion: injecting air, blowing bubbles, shaking,
whipping
Agglomeration: boiling liquids, super-saturated solutions
Characteristics of beer foam:

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Stability
Color
Texture (bubble size)
Adherence to glass (“lacing”)
More about foam…
 Pure
liquids and saturated solutions do
not form foams
 require
 Unstable

surface active agents--surfactants
foams:
Fatty acids, higher alcohols, inorganic salts
 Metastable

foams:
Soaps, detergents, proteins
 No
foam is thermodynamically stable
Types of foam
 Kugelschaum
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Small nearly spherical bubbles in thick, viscous fluid
 Polyederschaum
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Space-filled arrangement of polyhedral gas bubbles within thin
liquid films
Most common type of foam, thus most studied kind of foam
Why study beer foam?
 125
billion liters of beer brewed world
wide
 Along with clarity and color, one of the
first indicators of quality to be noticed
Who studies it?
 Beer

companies
Anheuser-Busch, Molson Brewery, Labatt
Brewing, South African Breweries and other
conglomerates
 Academics

Food scientists, physicists, chemists, chemical
engineers
What causes it?
 Nucleation
of super-saturated carbon
dioxide forms bubbles
 Formation of foam linear function of
CO2 content
 Bubbles entrapped by thin aqueous film
containing excess surfactant conc.
What improves foam?
 Natural:
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Barley proteins
Melanoidins
Polysaccharides
Hop resin acids
 Unnatural
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to beer:
Gum arabic
Albumin
Gellan gum
Enzymes to break apart naturally occurring proteins
increasing their concentrations
What impairs foaming action?
 Displacement
of a good frother with a
poor frother
 High
ethanol levels
 Fatty acids

di and trihydroxyoctadecanoic acids
 Lipids
 Detergents
 Ether
Foam stability
 Refers
to the time before the bulk foam
decays, depends on:
 Drainage
 Coalescence
 Elasticity
of the films
Foam structure
 Three
bubbles:
 Plateau’s
Border:
Drainage
 High
curvature of the border means that
the pressure of the liquid is lower than
that of the bulk film causing a flow of
liquid. (Shaw, 1992)
 Flow between two parallel plates:
Elasticity
 Prevents
breakage of the film as it thins
out due to mechanical stress
References
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Adamson A.W. 1990. "Physical Chemistry
of Surfaces", 5th Ed., John Wiley & Sons,
New York, pp. 544-550.
Bamforth, C. 2003. "Charlie Bamforth Brewing and Malting"
http://foodscience.ucdavis.edu/bamforth
Bikerman J. J. "Foams: Theory and
Industrial Applications", Reinhold
Publishing, New York. pp. 1-25, 40, 98-99,
180.
Bilinski C., Choi H., Mussar K. 1991. "Foam
stabilizing proteinase" United States Patent
5,035,902.
Clare K., Lawson M.A. 1990. "Foamstabilized malt beverage" United States
Patent 5,196,220.
Columbia Encyclopedia, Sixth Edition.
2003. "Beer"
http://www.encyclopedia.com/html/b1/beer.a
sp
Evans D.E. and Sheehan M.C. 2002. "Don't
Be Fobbed Off: The Substance of Beer
Foam-A Review" J. Am. Soc. Brew. Chem.
60(2): 47-57.
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Kobayashi N., Segawa S., Umemoto S.,
Kuroda H., Kaneda H., Mitani Y. 2002. "A
New Method for Evaluating FoamDamaging Effect by Free Fatty Acids" J.
Am. Soc. Brew. Chem. 60(1): 37-41.
Kunst A, Schmedding D.M.; van Schie B.J.,
Veenema M.J. 1997. "Emulsifier from yeast"
European Patent 0 790 316.
Lusk L.T., Goldstein H. and Ryder D.
"Independent Role of Beer Proteins,
Melanoidins and Polysaccharides in Foam
Formation" J. Am. Soc. Brew. Chem. 53(3):
93-103, 1995.
May K., Jeelani S.A.K., Panoussopoulos K.,
Hartland S. 1996. "Foam head and stability
of beer foams" Chemical and Biochemical
Engineering Quarterly 10(3), 107-112
Shaw D.J. 1992. "Introduction to Colloid and
Surface Chemistry", 4th Ed., Butterworths,
London, pp. 270-76.
Smith R.J. and Davidson D. 1998. "Natural
Foam Stabilizing and Bittering Compounds
Derived from Hops" J. Am. Soc. Brew.
Chem. 56(2):52-57.
Thank you!
 Comments?
 Questions?