Fats and oils

• Chemical structure of fats

  This is the basic chemical structure of a fat/oil:

  Fats are composed of the chemical elements: carbon, hydrogen and oxygen

  Fat molecules are made of one unit of glycerol and three fatty acids

  There are four specific reactions involving fats/oils that you need to know about to help you understand what happens when you make different recipes

  They are plasticity, shortening, aeration and emulsification
• What is plasticity in the context of fats?

  Ability to be shaped and spread
• Why can vegetable fat be spread onto bread?

  Due to its plasticity when pressure is applied
• What processes can be performed due to the plasticity of fats?

  • Spreading raw cake mixture into a tin
  • Piping buttercream onto cakes
  • Spreading cream cheese onto crackers
• What causes the plasticity of fats?

  Their chemical structure
• What are all fats primarily composed of?

  A mixture of triglycerides
• What do triglycerides contain?

  Different fatty acids
• Why do triglycerides have different melting temperatures?

  Because they contain different fatty acids
• How does the temperature affect the plasticity of butter?

  Chilled butter is hard; warmer butter is plastic
• What happens to butter as the temperature rises?

  It softens and becomes more plastic
• What is the final state of butter when heated sufficiently?

  It melts to become an oil
• What type of fatty acids do solid fats like butter and lard contain?

  A lot of saturated fatty acids
• How do saturated fatty acids affect the state of fats at room temperature?

  They tend to be more solid
• What is the relationship between unsaturated fatty acids and plasticity?

  More unsaturated fatty acids increase plasticity
• What is special about some vegetable fat spreads?

  They use triglycerides with low melting temperatures
• Why are some vegetable fats easy to spread right out of the refrigerator?

  They have good plasticity due to low melting temperatures
• What is plasticity?

  The ability of a fat to soften over a range of temperatures and be shaped and spread with light pressure
• What is shortening?

  The ability of fats to shorten the length of gluten molecules in pastry
• What is aeration?

  The ability of some fats to trap lots of air bubbles when beaten together with sugar
• What is emulsification?

  Either keeping drops of oil or fat suspended in a liquid and preventing them from separating out; or keeping drops of water suspended in an oil or fat and preventing them from separating out
• What is the texture of 'short' dough mixtures when baked?

  Tender, crumbly, 'melt-in-the-mouth'
• Why do 'short' dough mixtures have a tender texture?

  High fat content prevents gluten formation
• What is the term used for the fat in 'short' dough mixtures?

  Shortening
• What is the process of making shortcrust pastry?

  1. Cut butter or solid fat spread
  2. Rub into flour with fingertips
  3. Avoid melting the fat
  4. Ensure fat has plasticity
  5. Mixture becomes crumbly like breadcrumbs
• Why are fingertips used to rub fat into flour?

  They are the coolest part of the hand
• What happens to the mixture as fat is rubbed in?

  It becomes crumbly, resembling breadcrumbs
• What is observed under a magnifying glass when examining the mixture?

  Flour particles coated with waterproof fat
• What role does cold water play in making pastry dough?

  It binds the mixture and forms dough
• How do waterproof layers of fat affect gluten formation?

  They prevent long gluten molecules from forming
• What is the effect of short gluten molecules on pastry dough?

  They prevent the dough from being stretchy
• How does rolled out pastry dough behave compared to bread dough?

  It doesn’t spring back like bread dough
• What can fats like butter and vegetable fat spreads trap when beaten with sugar?

  Air bubbles
• Why can butter and vegetable fat spreads trap air bubbles?

  They have plasticity
• How do cooking oils compare to fats with plasticity in trapping air?

  They do not trap air as effectively
• What is the process of mixing fat and sugar together called?

  Creaming
• What happens to the mixture during the creaming process?

  The mixture becomes lighter in color and texture
• Why is the ability of fats to aerate the mixture important?

  It produces a light, spongy texture
• What does the raw cake mixture consist of?

  Flour, fat, protein, sugar, water, air bubbles
• What happens to water in the mixture as it bakes?

  It turns to steam
• What occurs to the fat in the butter during baking?

  It melts