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? Foam is a continuous liquid phase that

entraps gas Formed by two methods:

Dispersion: injecting air, blowing bubbles, shaking, whipping

Agglomeration: boiling liquids, super-saturated solutions

Characteristics of beer foam: Stability Color Texture (bubble size) Adherence to glass (“lacing”)

More about foam…Pure liquids and saturated solutions do

not form foams require surface active agents--surfactants

Unstable foams: Fatty acids, higher alcohols, inorganic salts

Metastable foams: Soaps, detergents, proteins

No foam is thermodynamically stable

Types of foamKugelschaum

Small nearly spherical bubbles in thick, viscous fluid

Polyederschaum 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

wideAlong 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 bubblesFormation of foam linear function of CO2

contentBubbles entrapped by thin aqueous film

containing excess surfactant conc.

What improves foam?Natural:

Barley proteins Melanoidins Polysaccharides Hop resin acids

Unnatural 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 stabilityRefers to the time before the bulk foam

decays, depends on: Drainage Coalescence Elasticity of the films

Foam structureThree bubbles:

Plateau’s Border:

DrainageHigh 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:

ElasticityPrevents breakage of the film as it thins

out due to mechanical stress

References 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. "Foam-stabilized malt beverage" United States Patent 5,196,220.

Columbia Encyclopedia, Sixth Edition. 2003. "Beer" http://www.encyclopedia.com/html/b1/beer.asp

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.

Kobayashi N., Segawa S., Umemoto S., Kuroda H., Kaneda H., Mitani Y. 2002. "A New Method for Evaluating Foam-Damaging 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?