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.
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.
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.
•
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
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
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
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
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
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.
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.
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.
•
Baking powder is added to plain flour to produce self raising flour.