Properties of Food: Fats & Oils (AQA GCSE Food Preparation & Nutrition)
Revision Note
Written by: Naomi Holyoak
Reviewed by: Lára Marie McIvor
Properties of food: fats & oils
Fats and oils provide food with several important characteristics
Shortening
The use of fats and oils when making dough allows the production of firm and crumbly baked foods, e.g.
shortcrust pastry
shortbread biscuits
Such products are described as having a 'short' texture, hence the fats and oils are said to have a shortening effect
The shortening effect of fats and oils is achieved by rubbing fat into the flour at the start of the dough-making process; this means that:
the flour is given a waterproof coating of fat
when water is added the proteins in the flour do not come into contact with the water and no gluten network can develop
rather than being stretchy and strong the resulting dough is crumbly and 'short'
markusspiske, via Wikimedia Commons
Aeration
Beating together fat and sugar, e.g. with a whisk or a wooden spoon, produces a mixture that contains many small air bubbles; this mixture is said to be aerated
Baking an aerated cake mixture results in a cake with a light and spongy texture
Public domain, via rawpixel
Plasticity
Fats are made of many molecules known as triglycerides, which can be saturated or unsaturated
Saturated triglycerides have a high melting point, so fats that are high in saturated triglycerides will be solid at room temperature, e.g. butter
Unsaturated triglycerides have a low melting point, so fats that are high in unsaturated triglycerides will be liquid at room temperature, e.g. olive oil
The different melting points of different triglycerides mean that fats soften over a range of temperatures; this property is known as plasticity
Fats can be soft at room temperature without being fully liquid, making them useful for:
spreading
shortening
creaming, i.e. beating together with sugar to form an aerated mixture
Public domain, via rawpixel
Emulsification
In most situations fats and water do not mix; an attempt to mix oil with water will usually result in water that contains large drops of oil, or in a layer of oil floating on top of the water
The two liquids are said to be immiscible
When oil and water are enabled to mix they form a mixture known as an emulsion
An oil in water emulsion contains tiny droplets of fat spread out in water, and will be a liquid, e.g.
milk
salad dressing
mayonnaise
A water in oil emulsion contains tiny droplets of water spread through fat or oil, and will be a solid, e.g.
margarine
butter
Emulsions can form in the presence of a substance known as an emulsifier; emulsifiers prevent fats and water from separating
The molecules within an emulsifier contain a hydrophilic and a hydrophobic region:
Hydrophilic = attracts water
Hydrophobic = repels water
To form a stable emulsion:
the hydrophilic region of an emulsifier forms an attraction with water and
the hydrophobic region forms an attraction with fat droplets
Emulsification diagram
Lecithin is an example of an emulsifier found in egg yolk; it allows mayonnaise to be produced
Mayonnaise is an emulsion formed from egg yolk, oil and vinegar
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