Biomedical Engineering Reference
In-Depth Information
4.2.3
Sourdough Storage
The liquid sourdough (DY 225-250) that is frequently used by bread manufacturers
in the United States is stored at 1-2°C, after rapid refrigeration, or at 4-5°C. It is
used to start a new fermentation within 2-3 days, without the refreshment step. In
the case of prolonged storage (10 days) one or two refreshments are needed to
activate the metabolism of the lactic acid bacteria and yeasts. A prolonged storage
of the sourdough for a few months at 4-5°C is possible when the ratio between
water and flour is reduced by adding flour at ca. 0.43:1 (30% water: 70% flour).
In this case, a firm sourdough, with DY of 143, is produced. Such a storage type
necessarily requires sourdough reactivation (at least two refreshments) before use
(
8
). In many artisan bread preparations, different and often empirical storage
techniques are applied. Generally, as a consequence of the daily schedule of bread
manufacture, a portion of the sourdough is refreshed at least one time before its
use. Nevertheless, by applying a separate storage protocol, part of the mother
sponge can be stored at low temperature (4-6°C) for some weeks after putting it
in a cloth bag tied with string (
9
). Refreshments are needed before reusing such a
sourdough in a bread-making protocol. In some cases sourdough can be frozen
and reused after refreshment.
4.3
Classi fi cation of Sourdoughs
Sourdough bread making is an ancient biotechnological process and various proto-
cols for its use are applied in many countries. On the basis of the technology applied,
sourdoughs have been grouped into three types (
10
), to which a fourth type, named
sponge-dough, can be added.
4.3.1
Type I Sourdough
Traditional sourdoughs whose microorganisms are kept metabolically active through
daily refreshments are included in this group. Type I sourdoughs are generally suit-
able for achieving dough leavening without addition of baker's yeast; the dough
propagation described above for French and U.S. sourdoughs are examples of Type
I sourdoughs. Generally, a three-stage protocol is applied relying on three refresh-
ments over 24 h in order to obtain the leavened dough to bake. Each step is charac-
terized by a given DY as well as fermentation temperature and time. At the end of
the last step of fermentation the sourdough is used as the leavening agent; thus it can
be considered as a natural starter culture containing many microbial strains (
11
) . In
wheat and/or rye flour sourdoughs, dominating strains belong to the species
Lactobacillus sanfranciscensis
which can co-exist with other obligately
