The sour taste of Sourdough
Bread actually comes not from the yeast, but from a
lactobacillus, with which the yeast lives in symbiosis.
The lactobacillus feeds on the byproducts of the yeast
fermentation, and in turn makes the culture go sour by
excreting lactic acid, which protects it from spoiling
(since most microbes are unable to survive in an acid
All breads used to be sourdoughs, and the
leavening process was not understood until the 19th
century, when with the advance of microscopes, scientists
were able to discover the microbes that make the dough
rise. Since then, strains of yeast have been selected and
cultured mainly for reliability and quickness of
Billions of cells
of these strains are then packaged and marketed as
"Baker's Yeast". Bread made with baker's yeast
is not sour because of the absence of the lactobacillus.
Bakers around the world quickly embraced baker's yeast for
it made baking simple and so allowed for more flexibility
in the bakery's operations. It made baking quick as well,
allowing bakeries to make fresh bread from scratch as
often as three times a day. While European bakeries kept
producing sourdough breads, in the U.S., sourdough baking
was widely replaced by baker's yeast, and only recently
has that country (or parts of it, at least) seen the
rebirth of sour-vinegar dough in artisan bakeries.
are most often made with a sourdough starter (not
to be confused with the starter method discussed above). A
sourdough starter is a culture of yeast and lactobacillus.
It is essentially a dough-like or pancake-like flour/water
mixture in which the yeast and lactobacilli live. A
starter can be maintained indefinitely by periodically
discarding a part of it and refreshing it by adding
fresh flour and water. (When refrigerated, a starter can
go weeks without needing to be fed.)
starters owned by bakeries and families that are several
human generations old, much revered for creating a special
taste or texture. Starters can be obtained by taking a
piece of another starter and growing it, or they can be
made from scratch. There are hobbyist groups on the web
who will send their starter for a stamped, self-addressed
envelope, and there are even mail-order companies that
sell different starters from all over the world. An
acquired starter has the advantage to be more proven and established
(stable and reliable, resisting spoiling and behaving
predictably) than from-scratch starters.
There are other
ways of sourdough baking and culture maintenance. A more
traditional one is the process that was followed by
peasant families throughout Europe in past centuries. The
family (usually the woman was in charge of bread making)
would bake on a fixed schedule, perhaps once a week. The
starter was saved from the previous week's dough. The
starter was mixed with the new ingredients, the dough was
left to rise, then a piece of it was saved (to be the
starter for next week's bread). The rest was formed into
loaves which were marked with the family sign (this is
where today's decorative slashing of bread loaves
originates from), and taken to the communal oven to bake.
These communal ovens over time evolved into what we know
today as bakeries, when certain people specialized in
bread baking, and with time enhanced the process so far as
to be able to mass produce cheap bread for everyone in the
A sourdough starter is a stable symbiotic culture of bacteria and
yeast present in a mixture of flour and water. The yeasts Candida
milleri or Saccharomyces exiguus usually populate sourdough cultures
symbiotically with Lactobacillus sanfranciscensis. Lactobacillus
sanfranciscensis was named for its discovery in San Francisco
Often a starter will consist of basic items
such as: water, bread flour, rye flour, and a sourdough starter
which can be purchased at certain grocery stores. Once the starter
is made, water and flour must be added in time increments over a
period of days. Depending on the locale of the bakery and the type
of bread being made, the starter can be either a relatively fluid
batter or a stiffer dough. Firm starters (such as the Flemish Desem
starter) are often more resource-intensive, traditionally being
buried in a large container of flour to prevent drying out.
fresh culture begins with a mixture of flour and water. Fresh flour
naturally contains a wide variety of yeast and bacterial spores.
When wheat flour contacts water, naturally occurring amylase enzymes
break down the starch into disaccharides (sucrose and maltose);
maltase converts these sugars into glucose and fructose that yeast
can metabolize. The lactobacteria feed mostly on the metabolism
products from the yeast. The mixture develops a balanced, symbiotic
culture after repeated feedings.
There are several ways to
increase the chances of creating a stable culture. Unbleached,
unbromated flour contains more microorganisms than more processed
flours. Bran-containing (wholemeal) flour provides the greatest
variety of organisms and additional minerals, though some cultures
use an initial mixture of white flour and rye flour or "seed" the
culture using unwashed organic grapes (for the wild yeasts on their
skins). Using water from boiled potatoes also increases the
leavening power of the bacteria, by providing additional starch.
Some bakers recommend un-chlorinated water for feeding cultures.
Adding a small quantity of diastatic malt provides maltase and
simple sugars to support the yeasts initially.
mixture can also be inoculated from a previously maintained culture.
The culture is stable because of its ability to prevent colonization
by other yeasts and bacteria as a result of its acidity and other
anti-bacterial agents. As a result, many sourdough bread varieties
tend to be relatively resistant to spoilage and mold.
and bacteria in the culture will cause a wheat-based dough, whose
gluten has been developed sufficiently to retain gas, to leaven or
rise. Obtaining a satisfactory rise from sourdough, however, is more
difficult than with packaged yeast, because the lactobacteria almost
always outnumber the yeasts by a factor of between 100:1 and 1000:1,
and the acidity of the bacteria inhibit the yeasts' gas production.
The acidic conditions, along with the fact that the bacteria also
produce enzymes which break down proteins, result in weaker gluten,
and a denser finished product.
San Francisco sourdough is
generally the same as a Type I sourdough. Type I sourdoughs have a
pH range of 3.8 to 4.5 and are fermented in a temperature range of
20 to 30 °C (68 to 86 °F); Saccharomyces exiguus leavens the dough,
Lactobacillus sanfranciscensis and L. pontis highlight a lactic-acid
bacterial flora that includes L. fermentum, L. fructivorans, L.
brevis, and L. paralimentarius.
In Type II sourdoughs Saccharomyces cerevisiae leavens the
dough, L. pontis and L. panis highlight the flora. These
sourdoughs have a pH less than 3.5 and are fermented within a
temperature range of 30 to 50 °C (86 to 122 °F) for several days
without feedings which reduces the flora's activity. This
process was adopted by some in industry, in part, due to
simplification of the multiple-step build typical of Type I
traditional sourdoughs.A primary-culture levain is prepared from
a salted wheat-rye dough, the process takes about 54 hours at 27
°C (81 °F) to build to a pH range of 4.4 to 4.6.
Sourdough starter can be used in two different manners.
Traditionally, a certain amount of sourdough starter (20 to 25
percent on average, depending on the water content of the starter)
is mixed into the bread dough, and the bread is kneaded and allowed
to rise as normal. The process is largely similar to using a pure
strain of baker's yeast, although some care must be taken since the
rise time of most sourdough starters is usually somewhat longer than
the average for typical baker's yeasts. (As a result, many sourdough
starters are unsuitable for use in a bread machine.)
When using a particularly liquid starter with a high
concentration of lactobacillus or acetic acid bacteria, the
large amount of lactic and acetic acids produced needs to be
managed carefully, since the acid can break down the gluten in
the bread dough; this becomes less of a concern in a stiffer
starter, where the yeast usually predominates.
manner of using sourdough starter is common for making quick breads
or foods like pancakes. It involves using baking soda (and sometimes
baking powder) to neutralize some or all of the acid in the starter,
with the acid-base reaction generating carbon dioxide to provide
lift to the dough or batter in a manner very similar to Irish soda
bread. This technique is particularly common in kitchens where the
starter is intentionally kept off-balance, with a substantially high
acid level, and is particularly associated with areas such as
Sourdough likely originated in Ancient Egyptian times around 1500
BC and was likely the first form of leavening available to bakers.
Sourdough remained the usual form of leavening down into the
European Middle Ages until being replaced by barm from the beer
brewing process, and then later purpose-cultured yeast.
from 100 percent rye flour, which is very popular in the northern
half of Europe, is usually leavened with sourdough. Baker's yeast is
not useful as a leavening agent for rye bread, as rye does not
contain enough gluten. The structure of rye bread is based primarily
on the starch in the flour, as well as other carbohydrates known as
pentosans; however, rye amylase is active at substantially higher
temperatures than wheat amylase, causing the structure of the bread
to disintegrate as the starches are broken down during cooking.
The lowered pH of a sourdough starter therefore inactivates
the amylases when heat cannot, allowing the carbohydrates in the
bread to gel and set properly. In the southern part of Europe,
where baguette and even panettone were originally made with
wheat flour and rye flour, sourdough has become less common in
recent times; it has been replaced by the faster growing baker's
yeast, sometimes supplemented with longer fermentation rests to
allow for some bacterial activity to build flavor.
was the main bread made in Northern California during the California
Gold Rush, and it remains a part of the culture of San Francisco
today. The bread became so common that "sourdough" became a general
nickname for the gold prospectors. The nickname remains in
"Sourdough Sam", the mascot of the San Francisco 49ers. A
'Sourdough' is also a nickname used in the North (Yukon/Alaska) for
someone who has spent an entire winter north of the Arctic Circle
and refers to their tradition of protecting their Sourdough during
the coldest months by keeping it close to their body.
sourdough tradition was carried into Alaska and the western Canadian
territories during the Klondike Gold Rush. Conventional leavenings
such as yeast and baking soda were much less reliable in the
conditions faced by the prospectors. Experienced miners and other
settlers frequently carried a pouch of starter either around their
neck or on a belt; these were fiercely guarded to keep from
freezing. Ironically, freezing does not kill a sourdough starter;
excessive heat does. Old hands came to be called "sourdoughs", a
term that is still applied to any Alaskan old-timer.
sourdough is the most famous sourdough bread made in the U.S. today.
In contrast to sourdough production in other areas of the country,
the San Francisco variety has remained in continuous production for
nearly 150 years, with some bakeries (e.g., Boudin Bakery among
others) able to trace their starters back to California's
It is a white bread characterized by a pronounced sourness
(not all varieties are as sour as San Francisco sourdough), so
much so that the dominant strain of lactobacillus in sourdough
starters was named Lactobacillus sanfranciscensis. Sourdough
also became popular because of its ability to combine well with
seafoods and soups such as cioppino, clam chowder, and chili.
Sourdough has not enjoyed the popularity it once had since bread
became mass-produced. However, many restaurant chains, such as
Cracker Barrel, keep it as a menu staple. Manufacturers make up for
the lack of yeast and bacterial culture by introducing into their
dough an artificially-made mix known as bread improver.
The most famous
sourdough bread made in the U.S. is the San Francisco
Sourdough, which in contrast to the majority of the
country has remained in continuous production for nearly
150 years, with some bakeries able to trace their starters
back to California's territorial period. It is a white
bread, characterized by a pronounced sourness (not all
sourdoughs are as sour as the San Francisco Sourdough), so
much so that the dominant strain of lactobacillus in
sourdough starters was named Lactobacillus sanfrancisco.