This section is from the book "The Steward's Handbook And Guide To Party Catering", by Jessup Whitehead. Also available from Amazon: Larousse Gastronomique.
Bread charged with gas the same as generated in soda fountains. The loaves are inclosed in a tight mould, gas forced into them, and baked. In baking, the gas expanding makes the bread light. The effect is similar to mixing acid and soda in the flour, but there is no residue of salts left in the bread by this method, and there is no loss of the flour as in fermentation, which process changes part of the flour to a gas which raises the bread. Companies with large capital are carrying on the aerated bread business in several cities. "The method of Dr. Dauglish, the results of which are now made so well known by the catering energy of the Aerated Bread Company, depends upon the fact that water may be made to hold within itself a large quantity of liquid carbonic acid under pressure, which it liberates as gas when the pressure is removed or diminished, as shown by soda water and other aerated liquids. The flour, with as much salt as is required, is placed in a strong air-tight vessel. In another strong vessel is water highly charged with carbonic acid under pressure, like soda water in bottle.
The two vessels communicate by a pipe with top; that containing the flour has a kneading apparatus working through an air-tight stuffing-box. On opening the tap the aerated water is forced into the kneading vessel in due quantity, and the flour is then worked into paste or dough while still under pressure. On removing the pressure the carbonic acid expands, as it does in uncorking a soda water or champagne bottle; but instead of escaping freely, as in these cases, it expands the dough. By a simple arrangement of a suitable outlet, the dough may be squirted out by the pressure of the gas within, and thus run into the form of a long cylinder of required thickness for cutting up into loaves, which must he baked without loss of time, as they would otherwise collapse".