Aerate. To incorporate air or CO2 during production to make the product more digestible and increase the volume.

Mixing flour, fat and water together in a bowl and then baking it  will produce an edible product, however, the chances that it will be palatable or very digestible are doubtful. However, by aerating these three ingredients a lovely light fluffy puff pastry can be produced, good to look at and very nice to eat..

There are  5  ways in which  Aeration of flour confectionery can be achieved

  1. Biological (panary, yeast ).
  2. Chemical (baking powder).
  3. Mechanical ( whisking and beating)
  4. Physical ( lamination, steam )
  5. Combinations of the above.


This refers to products that use Yeast as is main aerating method such as Bread, rolls, buns, crumpets, Dough cakes, Lardy cakes, babas, savarins etc. The aeration comes from the Carbon Dioxide produced when the  living yeast breaks down the sugars in the product. The gas is entrapped by the gluten structure, which then expands the product, giving it the lightness and crumb structure that is required.


Carbon Dioxide is produced chemically when an Acid and an Alkali interact, when in a solution and heated. This (1 part Alkali to 2 parts Acid ) is known as Baking Powder.

The main reaction should take place when the product is placed in the oven, until then, the product should be kept cold, so as to delay the reaction, a small amount of which will already have started due to the contact with liquid in the product.

The gas produced by the baking powder will be trapped in the small air cells created during mixing and held by the gluten network. This will expand on heating and increase the volume, which is then held by the coagulation of the gluten and any other proteins present, making the end product  light and digestible.

Products that do not have air entrapped through mixing ie Scones need to be made with  flour with a high quality gluten content. so that it will withstand the sudden generation and expansion of gas and retain it during the first part of baking until the protein has set allowing it to keep its form and volume.


When ingredients are beaten or whisked together using either hand, spatula , whisk or the appropriate attachments on a machine/blender and no baking powder used it is considered to be Mechanically aerated. Meringues are a good example of this form of aeration. Sponge goods are also a good example as the egg and sugar are whisked to a peak and then the flour is folded in, no other form of aeration is used.

Physical (lamination,steam).

When water reaches boiling point it produces water vapour, (steam) the gaseous phase of water. This,by its nature, increases in volume and if contained correctly will cause the product to expand. An example of this is Choux pastry. Water, fat, flour and egg are the only ingredients used but the end product is full of air, eg Eclairs and choux buns.  The only aeration is steam.

Puff pastry is also aerated by steam but it is assisted by the process of lamination.  Puff pastry is created by laminating layers of fat and dough. When the pastry is placed in the oven, the fat layers will melt before the water in the paste turns to steam. The hole created by the melting fat is then expanded by the steam until the protein finally coagulates and sets giving the classic light flaky pastry.

Combinations of above.

Danish pastries are aerated by a combination of Yeast and Lamination. A rich yeast fermented dough is laminated with fat, in the same way as puff pastry, the pastry is given a lift due to the process of lamination and at the same time the dough layers are softened and aerated by the action of the yeast.

If you wanted to make a traditional Victoria sponge cheaper by reducing the amount of egg, milk would have to be added to keep the moisture content. This would have an effect on the lifting properties and so to compensate, additional Baking Powder would have to be added to assist the aeration. this would mean that a combination of both mechanical and chemical aeration are used.

Generally the cheaper the cake the more Baking Powder is used.