1. Beer Foam Stability: From Head to Toe
John Stephenson
November 25, 2003
Prepared for Simon Hesp
Chem 348

2. What is beer? Barley Hops Yeast Steeped in water to germinate
Starches converted to sugars
Dried
Hops
Bitter flavor, aromatic scent
Yeast
Converts sugars to alcohol

3. 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”)

4. 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

5. Types of foam Kugelschaum Polyederschaum
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

6. 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

7. Who studies it? Beer companies Academics
Anheuser-Busch, Molson Brewery, Labatt Brewing, South African Breweries and other conglomerates
Academics
Food scientists, physicists, chemists, chemical engineers

8. 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.

9. What improves foam? Natural: Unnatural to beer: 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

10. 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

11. Foam stability
Refers to the time before the bulk foam decays, depends on:
Drainage
Coalescence
Elasticity of the films

12. Foam structure
Three bubbles:
Plateau’s Border:

13. 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:

14. Elasticity
Prevents breakage of the film as it thins out due to mechanical stress

15. References
Adamson A.W "Physical Chemistry of Surfaces", 5th Ed., John Wiley & Sons, New York, pp
Bamforth, C "Charlie Bamforth - Brewing and Malting"
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 "Foam stabilizing proteinase" United States Patent 5,035,902.
Clare K., Lawson M.A "Foam-stabilized malt beverage" United States Patent 5,196,220.
Columbia Encyclopedia, Sixth Edition "Beer"
Evans D.E. and Sheehan M.C "Don't Be Fobbed Off: The Substance of Beer Foam-A Review" J. Am. Soc. Brew. Chem. 60(2):
Kobayashi N., Segawa S., Umemoto S., Kuroda H., Kaneda H., Mitani Y "A New Method for Evaluating Foam-Damaging Effect by Free Fatty Acids" J. Am. Soc. Brew. Chem. 60(1):
Kunst A, Schmedding D.M.; van Schie B.J., Veenema M.J "Emulsifier from yeast" European Patent
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): , 1995.
May K., Jeelani S.A.K., Panoussopoulos K., Hartland S "Foam head and stability of beer foams" Chemical and Biochemical Engineering Quarterly 10(3),
Shaw D.J "Introduction to Colloid and Surface Chemistry", 4th Ed., Butterworths, London, pp
Smith R.J. and Davidson D "Natural Foam Stabilizing and Bittering Compounds Derived from Hops" J. Am. Soc. Brew. Chem. 56(2):52-57.

16. Thank you!
Comments?
Questions?