(1) Gluten
(2) Gluten and egg-white.
To show the framework, the gluten baked in the flour lessons should be used. It should be pointed out as the skeleton of the mixture which upholds the entire structure and on which the other ingredients depend. To have light mixtures, this framework must admit of being expanded and also of being stiffened permanently into the stretched shape. Since egg-white has both of these necessary qualities, it may be used for a framework either alone or in combination with gluten.
It should also be observed that a mixture of ingredients light in weight does not prevent the framework from rising as much as heavy ones do.
The pupils will see that the framework of a mixture must increase in size in order to make the mixture light, but it must be made very clear that, while heat stiffens any framework, it will not distend it. Some other agency is required for this.
5. Lightening agents used in flour mixtures:
(1) Air.—Incorporated by beating, kneading, and sifting.
(2) Steam.—Incorporated in the form of a liquid which, when heated, changes to steam.
(3) Carbonic acid gas.—Formed in the mixture by the chemical union of soda with some acid. Examples: soda and sour milk; soda, cream of tartar and water; soda and molasses.