Manufacturing Sourdough

Excerpted from

"Nature of the San Francisco Sour Dough French Bread Process, I. Mechanics of the Process"
by Leo Kline, T. F. Sugihara, and Linda Bele McCready in Baker's Digest 44(2), p48-50

The Spokesman-Review/Spokane Chronicle, Wed., Sept. 7, 1983.

U.S. Patent #3,734,743

San Francisco sourdough bread is made by the sponge-and-dough process. The heart of the process is the starter or mother sponge, a dough-like mixture of fermented flour and water teeming with microorganisms. This sponge is not only the source of the leavening and souring powers, it also provides the mechanism for perpetuating the process. In commercial practice, the sponge is rebuilt on the average of about every 8 hours, or at least 2 to 3 times a day, seven days a week. Each day a piece of straight dough or starter sponge is saved and refrigerated to be used as a starter sponge the following day. This starter sponge is used to make more starter sponges as well as sponges for bread production. This procedure has been carried on in this fashion for at least 100 years. The origin of the initial sponge is veiled in mystery.

The starter sponge is made according to the following formula:

100 parts previous sponge
100 parts flour (high-gluten)
50 parts water

The sponge is made up and held 7-8 hrs. at 80F. Starting pH: 4.4 to 4.5. Final pH: 3.8 to 3.9.

The bread dough is made up with the fully-developed starter sponge, flour, water and salt according to the following formula:

100 parts flour (regular patent)
60 parts water
20 parts starter sponge (11% of total dough weight)
2 parts salt
Make up – approx. 1 hr floor time – then proof 8 hr. 86F
Starting pH: 5.2 to 5.3. Final pH: 3.9 to 4.0.

It takes over six hours to make the bread. Huge mixers are loaded with unbleached flour and water. 70 pounds of starter are added to each 600-pound batch of sourdough. A portion of sponge is retained as starter for the next day's batch. The starter is partly responsible for the hard crust of the bread, as well as steam in the first 10 minutes of baking.

After mixing, the dough is allowed to relax for at least 30 minutes, placed in a divider (scaled) which divides the dough into loaves of uniform weight. Next, the loaves are shaped in a rounder machine and deposited into rows of canvas carriers which are dusted with rice flour and/or corn meal. It is then proofed in an overhead proof box for about 20 minutes at 90F. The loaves are then placed into a molder. The molder forms the loaves into the desired shape. The bread is moved along automated lines on bread boards dusted with corn meal. From the molder, the bread goes into another proof box where it is allowed to proof for six to eight hours at 85F to 90F. This long proofing time may be reduced somewhat by increasing the proportion of starter sponge or by lengthening the floor time before molding, but is generally essential for development of the acidity and the coarse grain typical of this bread, as well as for volume. The pH of the bread dough on make-up is about 5.3 and drops to about 3.9 when the long proof is completed, or roughly to the same point reached by the starter sponge itself.

It is essential to slash or make cuts on the surface of the fully-proofed dough just before it is placed in the oven, otherwise the crust will be wrinkled and generally unsatisfactory. After slashing, the bread is placed into the oven.

The bread is baked for 40 to 55 minutes at 375F to 420F. The Toscana bakery in Oakland had a 95-foot tunnel oven which had one gas burner and drive line rather than the three of each in some other commercial bakery ovens.