Book of American Baking / A Practical Guide Covering Various Branches of the Baking Industry, Including Cakes, Buns, and Pastry, Bread Making, Pie Baking, Etc.

by Various

The Older or Vienna Process.

Fermentation of the Mash.—At the completion of the acidulation of the mash it is at once cooled to 77 degrees F. This is accomplished by continuously agitating the mash by mechanical means with hollow plungers that are filled with ice or cold water, and which at the same time serves to aerate the mash.

The former method of cooling the mash in shallow vats, on account of infection and introduction by and of undesirable bacteria from the atmosphere into the mash, has been generally discarded.

Fermentation is now introduced by adding a certain quantity of compressed yeast, which must be free from starch adulteration.

In a short time a head begins to develop upon the surface of the mash, which gradually grows and rises to the top of the half-filled vats. The period of fermentation depends upon the temperature of the mash as well as the density of the mash.

The higher the density of the mash, the more vigorous the fermentation.

In general, the time consumed for proper fermentation is twelve to eighteen hours.

As fermentation proceeds, the density of the mash becomes less, while the yeast cells increase, and at the same time the temperature of the mash raises.

Fig. 8.
Yeast Cells Fully Developed.

The mash in this process contains the whole of the grains, and for this reason the head, which contains the yeast cells, and which is skimmed off as it rises, must be strained; it is subsequently washed and then pressed. In contrast to this method the newer or “Aeration Process” for the production of yeast presents entirely different phases.