Presentation on theme: "Beer Foam Stability: From Head to Toe"— Presentation transcript:
1 Beer Foam Stability: From Head to Toe John StephensonNovember 25, 2003Prepared for Simon HespChem 348
2 What is beer? Barley Hops Yeast Steeped in water to germinate Starches converted to sugarsDriedHopsBitter flavor, aromatic scentYeastConverts 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, whippingAgglomeration: boiling liquids, super-saturated solutionsCharacteristics of beer foam:StabilityColorTexture (bubble size)Adherence to glass (“lacing”)
4 More about foam…Pure liquids and saturated solutions do not form foamsrequire surface active agents--surfactantsUnstable foams:Fatty acids, higher alcohols, inorganic saltsMetastable foams:Soaps, detergents, proteinsNo foam is thermodynamically stable
5 Types of foam Kugelschaum Polyederschaum Small nearly spherical bubbles in thick, viscous fluidPolyederschaumSpace-filled arrangement of polyhedral gas bubbles within thin liquid filmsMost 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 conglomeratesAcademicsFood scientists, physicists, chemists, chemical engineers
8 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.
9 What improves foam? Natural: Unnatural to beer: Barley proteins MelanoidinsPolysaccharidesHop resin acidsUnnatural to beer:Gum arabicAlbuminGellan gumEnzymes to break apart naturally occurring proteins increasing their concentrations
10 What impairs foaming action? Displacement of a good frother with a poor frotherHigh ethanol levelsFatty acidsdi and trihydroxyoctadecanoic acidsLipidsDetergentsEther
11 Foam stabilityRefers to the time before the bulk foam decays, depends on:DrainageCoalescenceElasticity of the films
13 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:
14 ElasticityPrevents breakage of the film as it thins out due to mechanical stress
15 ReferencesAdamson A.W "Physical Chemistry of Surfaces", 5th Ed., John Wiley & Sons, New York, ppBamforth, 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 PatentLusk 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, ppSmith R.J. and Davidson D "Natural Foam Stabilizing and Bittering Compounds Derived from Hops" J. Am. Soc. Brew. Chem. 56(2):52-57.