Raising Agents

1
Raising Agents 

• Raising Agents are gases which are introduced
  into a food mixture
• During the mixing process
• In a substance which is added to the mixture
• The gas is incorporated or released when
  ingredients are combined.
• On heating (baking), the minute bubbles of gas
  enclosed in the mixture expand, causing the
  mixture to rise.
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2

• The three most common raising agents are steam,
  air and carbon dioxide.
•  
• They are frequently used in combination with each
  other
• e.g. in a creamed cake mixture -
• Steam from liquid (egg/milk/water)
• Air beaten in (creaming butter sugar)
• Carbon dioxide from chemical raising agents in
  baking powder or self raising flour.

3
Steam

• Some food products have steam as the main raising
  agent. These products must contain a high
  proportion of liquid, e.g. Choux pastry, batter
  used for Yorkshire puddings.
• For steam to make the mixture rise, two
  conditions are needed
• A large proportion of liquid (Milk/Water)
• A high baking temperature of 200oC or above
•  
• During baking
• Liquid reaches boiling point
• Steam forces its way up through the mixture,
  stretching the mixture and making it rise.
• The steam escapes and is replaced by air, the
  mixture bakes and sets into the risen shape.
• Sometimes steam is trapped inside. It condenses
  on cooling and then the product collapses. This
  often happens in Yorkshire puddings.
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4
Air

• Mechanical action incorporates air into mixtures,
  it is the main raising agent in some food
  products, e.g. whisked sponge cakes and soufflé
•  
• Air can be mechanically introduced into mixtures
  by
• Sieving flour air is trapped between fine
  particles
• Rubbing fat into flour air is trapped between
  breadcrumbs
• Creaming fat and sugar air is beaten in, to
  form an air and fat foam.
• Whisking eggs/sugar or egg whites air is
  whisked ino the egg to form a high volume foam
• Beating batter air is beaten in, but steam is
  the main raising agent.
• Rolling and folding pastry air is trapped
  between the layers
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5
Carbon Dioxide

• This is produced in two ways
• Biologically from yeast cells during the
  fermentation process
• Chemically from the action of bicarbonate of soda
  with an acid
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6
Biological Raising Agents

• Yeasts are micro organisms, during the
  fermentation process, the yeast cells feed on
  sugar and reproduce to produce carbon dioxide.
•  
• Certain factors affect the action of yeast -
• Temperature optimum temperature range is 25oC
  35oC
• Above 60oC the fermentation process is
  destroyed
• Below 25oC the reaction is slowed down
• Fresh yeast can be frozen without killing
  it and it becomes active again once defrosted.
•  
• Moisture This is provided from milk/water/egg
•  
• Food During fermentation of yeast, the cells
  need to be fed on sugar to produce carbon
  dioxide. There is also a small amount of sugar in
  the flour
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7
Chemical Raising Agents

• Carbon dioxide is produced from chemical
  reactions. This can be made to happen in many
  recipes by the addition of a chemical raising
  agent.
•  
• Chemical raising agents must be measured
  accurately, they
• Are used in small quantities
• Are easy to use and often already combined e.g.
  self raising flour
• Will produce controlled amounts of carbon dioxide
  
• to aerate mixtures evenly.
•  
• Three types of chemical raising agent are -
• Bicarbonate of Soda known as sodium
  bicarbonate
• Bicarbonate of Soda Acid (alkali acid)
• Baking Power or baking powder in self raising
  flour

8

• Bicarbonate of Soda -
• Simplest type of chemical raising agent. When
  heated in a mixture, it produces sodium carbonate
  (soda) steam and carbon dioxide.
• The carbon dioxide and steam aerate the mixture.
  The soda leaves a dark yellow colour and gives a
  sharp alkaline taste to the mixture.
• Used in recipes which have other strong flavoured
  ingredients e.g. chocolate cake gingerbread
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• Bicarbonate of Soda plus Acid
• The bicarbonate of soda reacts with the acid to
  produce carbon dioxide. The acid helps to
  neutralise and prevent the taste and colour
  residue left when bicarbonate of soda is used on
  its own.
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• A traditional source of acid is sour milk. This
  is still used in some mixtures, an other sources
  of acid is Cream of Tartar (Tartaric Acid), when
  combined with bicarbonate of soda this releases
  the carbon dioxide slowly, leaving a tasteless
  salt behind. The ratio used is 2 parts Tartar to
  1 part bicarbonate of soda.
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• Baking Powder
• Commercial mixture of bicarbonate and acid
  substances ready mixed in the correct
  proportions. A buffer is added in the form of
  cornflower or rice flour to absorb any moisture
  and prevent the reaction taking place in the
  storage container.
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• Baking powder is added to plain flour to produce
  self raising flour.