When worlds colloid
Press play : Banger's got something to say about mixtures.
Try the activities below for more colloids and emulsions in cooking
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Mixtures: solutions, colloids and suspensions
The physical structure of foods affects the way they are perceived and processed by the body. In science, a mixture is when one or more substances combine without chemically reacting. Food mixtures are commonplace. Cheese, jelly, jam, butter and chocolate are all examples of mixtures. Mixtures can be further classified into three types: solutions, colloids and suspensions. Many commonly found foods, including most dairy products, are colloids or suspensions. Other examples of colloidal foods are jam, jelly and tomato sauce. The particles in colloids are small enough to be evenly distributed throughout the mixture and won't settle to the bottom of a container. The particles in a colloid also give structure, texture and mouth-feel to foods. Based on the phase of the dispersed substance/ phase it is dispersed in, colloids can be further classified as: Sols - solid particles in a liquid (jelly, jam) Emulsions- liquid particles in a liquid or solid- need an emulsifying agent to bind them (milk, mayonnaise, butter, peanut butter, cheese). Foams- gas particles in a solid or liquid (meringue, bread, ice cream, whipped egg white, whipped cream) Aerosols- small particles of liquid or solid dispersed in a gas (smoke, fog) When cooking, being aware of how the components of colloids behave under different conditions can greatly affect the appeal of a finished dish. Water and oil don’t mix, except for when it comes to emulsions.
Fat and water are considered immiscible - they don't mix. When two molecules don't mix they align themselves in a way to touch as little as possible. However, Emulsions are immiscible liquids dispersed into one another. An emulsion consists of two "phases": the dispersed phase and the continuous phase. The even dispersion of immiscible particles in emulsions is made by using an emulsifier, preventing the colloid from coalescing (rejoining). At the molecular level, emulsifier molecules have two distinct ends: one end prefers water (hydrophilic) and the other does not (hyrophobic). They coat the surface of oil droplets, making them evenly dispersed throughout an emulsion. Lecithen, found in soy oil and egg yolk is a commonly used emulsifier. Other emulsifiers useful for kitchen cooking include mustard, garlic, tomato paste and cream. Emulsifiers offer other benefits: they act as a preservative: to keep bread fresh, or to stop cakes from sticking to the tin. Run the animations to see what happens to an emulsion if an emulsifier is not present.
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