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Beer Foam Stability: From Head to Toe

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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Beer Foam Stability: From Head to Toe

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

  2. What is beer? • Barley • 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 • 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 • 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: • 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. 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.

  16. Thank you! • Comments? • Questions?

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