Aeration
Aerated bread is leavened by carbon dioxide being forced into dough under pressure. From the mid 19th to 20th centuries bread made this way was somewhat popular in the United Kingdom, made by the Aerated Bread Company and sold in its high-street tearooms. The company was founded in 1862, and ceased independent operations in 1955. While it had some devoted adherents, it never eclipsed the use of baker's yeast worldwide.
The Pressure-Vacuum mixer was later developed by the Flour Milling and Baking Research Association at Chorleywood. With the application of both pressure and vacuum at different points in the mixing process, this mixer not only manipulates the gas bubble size, it may also manipulate the composition of gases in the dough via the gas applied to the headspace.[23]