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Week 3: Protein - Foams - Coggle Diagram

- - - - Typically involves protein forming a protein film around the gas bubble to retain the gas bubble in the overall structure.
        
        Provides volume and distinctive mouthfeel to products such as whipped cream and ice cream, breads etc.
      - vs Emulsion: similar to emulsion :check:
        
        Both contains a hydrophilic and hydrophobic portion
        
        Emulsion: liquid/water (hydrophilic), oil (hydrophobic)
        
        Foam: liquid/water (hydrophilic), gas/air (hydrophobic)
        
        Gas and water interface must be protected by a surface interfacial film
        
        Bubbles in foam tend to be bigger than the droplets in emulsions
      - Egg Yolk Foams :check:
        
        Utilised in certain baked products such as sponge cakes and puffy omelettes
        
        Quite heavy compared to white egg foams
        
        As yolk foams are beaten, volume increase and reduction in yellow foam colour can be observed. Final result is a moderately thick, light yolk foam
      - Egg White Foams: Created by agitation of egg albumen where air is incorporated and air bubbles are created by beating the proteins
        
        Typical stages of egg white foam development in culinary terms
        :check:
        
        Soft rounded peaks: Glossy foam edges that keep some shape but droop once lifted
        
        Air cells are small, foam white, egg white volume increased
        
        Typically used for soft meringue
        
        Stiff Peaks: Glossy and defined foam edges that hold their shapes, stand straight once lifted
        
        Many small air cells, volume increased, egg white protein has coagulated around fine air cells
        
        Ideal for making soufflés and sponge cakes, where further expansion occurs during baking. Perfect for shaping and decorating and piping
        
        Dry Peaks: Dull and firm foams that appears lumpy and crumbly
        
        Foam is brittle, inelastic, less volume as air cells are broken
        
        Commonly used to make very soft-textured frothy meringue e.g. floating islands or stiff cookie batter
        
        Ingredients that Affect Egg White Foam Stability :check:
        
        Sugar
        
        Increase viscosity of liquid (Need more time to create air cells), aids stability
        
        Delays foam formation significantly
        
        Increased beating result in foam with finer texture and increased surface area
        
        Acid e.g. cream of tartar or lemon juice: Added early in the formation of foam
        
        Reduces pH – reduces the charge on the protein molecules, bringing them closer to their isoelectric point, making it stronger, more stable interfacial foam
        
        Isoelectric point (IEP) is the pH at which a particular molecule or surface carries no net electrical charge
        
        Formation of foam is delayed by addition of acid results in greater agitation and finer, more stable foam
        
        Salt
        
        Adds flavour
        
        Produces a drier foam with less volume and reduced stability
        
        Liquid
        
        Dilutes proteins in foam hence decreases stability (less proteins to coat the air bubbles)
        
        Gums & Other thickening agents
        
        Increase viscosity of continuous phase may promote stability of foam
        
        Factors that Affect Volume of Egg White Foam
        
        Temperature of whites:Surface tension is greater in whites when it is just removed from fridge
        
        Quality of white
        
        Thick white requires more beating to reach the desired end point but foam holds volume well
        
        Thin white forms foams quickly and reaches a large volume
        
        Type of beater used (eg Handwhisk vs Electrical whisk)
        
        Extent of beating
        
        Contamination of white with yolk – negative impact on volume
        
        Acid – reduce volume
        
        Sugar – increases volume
        
        Water – positive impact on volume but increases the likelihood of syneresis, decreasing stability
      - How to Produce Stable Foams :check:
        
        Prevent film rupture, liquid drainage (losing elasticity of film) and evaporation
        
        Stabilise gas bubbles by the presence of a stable interfacial layer, resisting rupture
        
        Surface tension is low
        
        A substance solidifies on the surface of the bubbles
        
        Liquid phase/continuous phase must have low vapour pressure: doesn’t evaporate readily at storage
        
        Vapour pressure is low
        
        Minimise drainage by increasing viscosity of continuous phase
        
        Stability is determined by measuring drainage of liquid over time
        
        Foam stability may be reduced due to:
        
        Gravity
        
        Liquid film drains due to gravity.
        
        Film surrounding the gas bubbles becomes very thin. Gas escapes, volume of foam shrinks
        
        Evaporation of continuous phase: Gas bubbles burst and foam volume reduced
        
        Coalescence
        
        Diffusion of gas from small bubbles to large ones
        
        Fewer bubbles, foam volume shrinks