BLBS102-c31 BLBS102-Simpson March 21, 2012 14:0 Trim: 276mm X 219mm Printer Name: Yet to Come
31 Bakery and Cereal Products 603Defined cultures have also been marketed; however, the suit-
ability of Type I and Type II cultures appears to outcompete
the alternatives offered. In addition to baker’s yeast, the col-
lection of defined cultures comprise at least pure cultures of
Lb. brevis(heterofermentative) andLb. delbrueckiiandLb. plan-
tarum(homofermentative). The homofermentative cultures pro-
duce mainly lactic acid under anaerobic conditions, whereas
the heterofermentative cultures will also produce acetic acid or
ethanol and carbon dioxide. By controlling, if possible, the con-
tributions from these different cultures, the relative amounts
of acetic and lactic acids may be regulated. This important
relationship:
Lactic acid (Mole)
Acetic acid (Mole)
is called the fermentation quotient (FQ).
Relatively mild acidity will have an FQ about 4–9, whereas
a more strongly flavored rye bread, as produced in Germany,
requires a much lower FQ, for example, 1.5–4.0 (Spicher
1983, Gobbetti and Corsetti 1997, Hammes and Ganzle 1998, ̈
Martinez-Anaya 2003, Stolz 2003).Sourdough ProcessesSeveral more or less traditional sourdough processes are
practiced on a large scale in present-day bakery industry.
(Fig. 31.5) One line comprises processes designed for bak-
ing with rye flour. They may be the Type I processes men-
tioned above. The Berliner short-sour process, the Detmolderone-stage process, and the L ̈onner one-stage process are typ-
ical for central and northern Europe. In every case, the pro-
cess is initiated by a starter culture, 2–20% (often, 9–10%),
in a rye flour–water (close to 50:50 w/w) mixture that is in-
cubated for 3–24 hours at 20–35◦C, depending on the pro-
cess. When the resulting sourdough is ready, bread making
starts with an “inoculation” of about 30% sourdough together
with rye flour, wheat flour, baker’s yeast, and salt. The final
rye:wheat ratio is regularly 70:30 w/w. Dough yield is ad-
justed to satisfy handling (e.g., pumping) and microbial nutrition
requirements.
Another line of sourdough processes comprises those for bak-
ing with wheat only. The San Francisco sourdough process is
often mentioned in this connection; however, Italian wheat sour-
dough products, for example, Panettone, Colomba, and Pandoro,
are also very important (Cauvain 1998, Gobbetti and Corsetti
1997, Spicher 1983, Wood 2000).
The starter for San Francisco sourdough is ideally rebuilt ev-
ery 8 hours to maintain maximum activity. However, a mature
sponge may be kept refrigerated for days with acceptable per-
formance. For rebuilding the starter, sponge (40%) is mixed
with high-gluten wheat flour (40%) and water (about 20%) to
ferment at bakery temperature. Final bread making requires a
dough consisting of the ripe sourdough (9.2%), regular wheat
flour (45.7%), water (44.2%), and salt (0.9%). Proofing for
7 hours follows, during which the pH decreases from about 5.3 to
about 3.9. A sourdough starter culture for San Francisco French
bread production commonly containsLb. sanfranciscensisand
Candida holmii.Figure 31.5.The sourdough process.