Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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This is also limited by the consistency of the dough;

soft dough (low consistency) requires a higher tem-

perature than hard dough (high consistency). In hard

dough, where there is less water to evaporate, high

temperatures produce cracks because dehydration is

too rapid. If the temperature is too high, an overdone

thick crust and, unbaked crumb result.

0005 Depending on the type of bread, the temperature

during baking will be uniform or will be higher at

the beginning of the baking process with a slowly

decreasing temperature afterwards.

Duration of Baking

0006 The duration of baking depends on the temperature

used. During baking, the following changes take

place: gelatinization of the starch, denaturation of

the protein, and the formation of aromatic substances.

Thus, the duration of baking is limited, on the one

hand, to a minimum in which all these changes are

produced and, on the other hand, to a maximum

limited by the loss of vitamins, excess evaporation of

water, and also economic considerations.

Relative Humidity

0007 The injection of water vapor into the oven favors the

increase in relative humidity. The dough is covered

with a fine surface layer of water, which keeps it moist

and elastic for some time. This presents the following

advantages: it avoids the immediate formation of

crust, increases the volume (with a satisfactory oven

spring), improves the color and shine, and produces

a fine crust. Any excess water leads to the formation

of drops of water on the surface of dough that give

rise to bubbles on the bread.

Type of Oven

0008 Heat is transferred by conduction, convection, and

radiation. Coal, oil, or electricity may be used to heat

the oven. There are several different types of oven, the

most common being the hot air oven, in which the air

is heated in a closed system and introduced into the

oven by forced convection. Other types include the

rotary hearth oven, the reel oven, the pan rack oven,

and a continuous belt or tunnel oven.

Baking Process

0009 The dough is placed into the oven when it reaches its

optimum fermentation. If the fermentation is too

short, the dough has not matured enough (under-

oxidized or green dough), and when it is placed into

the oven, it does not support the increase (oven

spring), resulting in a flat bread. If there is overfer-

mentation (overoxidized dough), the crumb is very

rough. To make bread with a crunchy crust, a cut is

made on the dough before placing it into the oven.

The cut should be oblique so that some of the wet

zones are protected, thus achieving a greater volume

of bread, because it can support the pressure better; if

the cut is vertical, the bread opens and dries.

0010Transfer of heat Once placed into the oven, the

dough increases its volume, reaching a maximum

volume after some 5–10 min, depending on the

weight, size, and quality of the dough. This increase

in dough volume is due to the heat in the oven.

Convection and radiation from the walls of the oven

heat the dough, which comes into contact with the

hot air. Dough on the baking pan is heated by con-

duction. The heat is transferred by conduction from

the outside to the core of the dough, so the dough

reaches different temperatures, leading to the forma-

tion of a crust on the surface (> 100



C) and the crumb

inside (< 100



C) the bread.

0011Evaporation of water When the dough reaches

100



C, water inside evaporates. This process occurs

superficially and water moves from the inside to the

outside. When the migration of water is slow, the

crust begins to form, the thickness of which depends

on the duration of baking. At the beginning of baking,

steam is added to help development and increase the

bread volume. Later, the bread itself produces the

steam, which condenses on the surface of the dough.

The dough thus remains moist for longer, acquiring a

satisfactory oven spring, and the surface is prevented

from drying too rapidly. The resulting bread has a

good external quality, color and shine, with a thick,

crunchy crust.

0012Vaporization of aromatic substances During bak-

ing, together with the evaporation of water, there is

also vaporization of all compounds that have a

boiling point of less than 100



C, particularly ethanol,

carbon dioxide, and some aromatic compounds

formed during fermentation and baking (e.g., alde-

hydes, esters, and volatile acids). The vaporization

depends not only on the concentration of these sub-

stances in dough but also on the capacity of gas

retention in the dough and the permeability and

elasticity of the network.

0013Cooling It is very important to cool the bread cor-

rectly after baking, otherwise the bread will crumble

upon slicing. Cooling is also very important if

the bread needs to be packed. The moisture of the

crumb becomes crust during cooling. Depending on

the relative humidity of the environment, the bread

will lose or take up excessive moisture, and this will

affect the quality of the bread.

BREAD/Chemistry of Baking 635

Physical–Chemical Changes During

Baking

0014 Baking converts the dough into the final baked prod-

uct by firming (stabilization of the structure) and by

the formation of characteristic aroma substances.

There are three phases depending on the temperature

the dough reaches:

0015 oven spring (enzyme active zone) (from 30 to 60

or 70



C);

0016 gelatinization of starch (55–60



C) to no higher

than 90



0017 browning and aroma formation above 100



Oven Spring

0018 In this stage, the dough temperature reaches about



C. There is very intensive fermentation because

yeast activity continues until the dough reaches about



C. Enzymatic activity is also very high because of

the high temperatures, with a maximum at about



C, and causes the conversion of starch to sugars.

There is a liquefaction of dough and decrease in

viscosity. The enzymatic activity continues until the

dough reaches about 80



C. There is an increase in the

production of carbon dioxide from the conversion of

sugar by the action of yeast. The solubility of carbon

dioxide decreases with increasing temperature, and

the production of carbon dioxide ceases when the

yeast dies.

0019 With the action of heat, the gas pressure increases.

There is an inverse relationship between the size of

the gas bubbles and gas pressure: the smaller the

gas bubble, the higher the gas pressure. If the flour

is of a poor quality, the gas bubbles cannot with-

stand the pressure and widen; then, the pressure de-

creases, and the resulting bread is flat (the bread

deflates).

0020 Enzymatic activity has an influence on the struc-

ture, crumb quality, and volume of the bread. If there

is little enzymatic activity, the bread is small because

the structure of the starch becomes rigid too soon,

whereas too much activity leads to a structure that is

too fluid, and the bread collapses completely.

Gelatinization of Starch

0021 Dough undergoes increases in temperature from

50–60



Cto90



C. This promotes the gelatinization

of starch and the denaturation of protein with the

coagulation of gluten. The denaturation of protein

begins at about 70



C and is important for a stable

bread structure. During kneading, the proteins are

hydrated by the absorption of water, and during

baking, water is transferred from gluten to starch,

which swells. This dehydration of gluten continues

until the increase in temperature leads to gluten

coagulation. The denaturation of protein is more

intensive on the crust than in the crumb of the

bread because of the high temperature on the crust.

0022The capacity of starch to absorb water depends on

the quantity of starch damaged during milling. First,

starch absorbs the free water in the dough. It swells,

and in the oven, the starch begins to gelatinize due to

the high temperature. During baking, the gluten gives

up water to starch, and the gelatinization is complete.

The starch undergoes several changes such as loss of

birefringence, increase in viscosity, and exudation

of amylose (very important during staling). Dough

undergoes an increase in viscosity by gelatinization

of starch, and the dough becomes more consistent.

The plasticity decreases, and the rigidity of the dough

increases. When the gluten collapses, starch supports

the structure of dough. During cooling, starch crys-

tallizes, contributing to the firmness of bread. These

changes in starch brought about by the action of heat

may be measured using an amylograph, which gives

an idea of the behavior of the flour in breadmaking

and the retrogradation of starch, associated with

staling. (See Starch: Functional Properties.)

Browning and Aroma Formation

0023The reaction of starch is different inside and outside

the dough due to the different temperatures. The

temperature outside the dough is more than 100



there is a high degree of evaporation of water on the

surface, and crust formation and coloration begin.

The temperature inside the dough is less than

100



C, which leads to crumb formation. The crumb

in the center of the dough and the crumb near crust

are different.

0024Color develops on the crust, as a result of the

temperatures reached in the oven. Thus, the tempera-

ture and the time in the oven affect the color of the

crust and the aroma of the bread. There are two

different reactions: browning (or the Maillard reac-

tion) and sugar caramelization. The formation of

different aromatic compounds influences the color,

aroma, and flavor of bread. Different dough ingredi-

ents, especially salt and sugar, also influence the

flavor. The Maillard reaction is the reaction between

reducing sugars (glucose, fructose) and the amino

group of proteins to form dark brown melanoidins

and other intermediate compounds such as maltol,

isomaltol, and a-dicarboniles. Sugar caramelization

is brought about by dehydration of sugar, as a result

of the high temperatures, to form very reactive

aldehydes (furfural aldehydes) and other dark

compounds, which may form the polymers or react

with the amino compounds, furan derivates, and

isomaltol.

636 BREAD/Chemistry of Baking

0025 It is principally the quantity of the aromatic com-

pounds formed during fermentation that determines

the aroma of bread, but the compounds formed

during baking as a result of browning reactions and

formation of melanoidins and caramel polymers also

have some influence. Some of the aroma components

detected include 1-propanol, acetaldehyde, propanal,

butanal, furfural, acetic acid, and ethyl acetate. The

more volatile compounds are evaporated during

baking, as mentioned before. Depending on the

quality of the network, gas-retention capacity, and

permeability, the aroma will be more or less retained

by the bread. The different types of bread also have

different aromas and intensities. (See Browning:

Nonenzymatic; Flavor (Flavour) Compounds: Struc-

tures and Characteristics.)

Development of Bread

0026 The factors that influence the development of bread

are as follows: the quantity and quality of gluten, the

quantity of sugars (owing to their capacity to produce

gas), and the quantity of yeast, salt, and other ingredi-

ents such as fat. Other technological factors include:

the breadmaking process and duration of fermenta-

tion, temperature of baking, duration of baking, and

characteristics of dough pieces.

0027 During baking, there is an increase in dough

volume owing to the following: (1) water in the aque-

ous phase in dough is vaporized by the action of heat;

(2) carbon dioxide retained in the dough is dilated by

the heat; and (3) the network becomes more elastic,

owing to the change in thiol/disulfide bonds between

adjacent protein chains, and favors a satisfactory

oven spring.

0028 Thus, the dough development is related to the

following factors: the concentration of gas, the

elasticity and resistance of the network, and the gas-

retention capacity. If the dough has a high elasticity

and a great capacity to retain gas, the bread will rise

greatly, have a less specific weight, and have a

uniform soft crumb, whereas, if the dough has little

elasticity or little gas-retention capacity because of a

short and rigid network, the bread will be small, with

a nonhomogenous alveolus and agglomerate crumb.

Loss During Baking

0029 During baking, dough loses weight mainly from

evaporation of water (about 95%) and minimally

from vaporization of ethanol, CO

, volatile acids,

and esters. These losses occur principally on the

crust, which withstands higher temperatures than

the crumb, which contains more moisture. A short

baking time reduces the weight loss, but the resulting

bread is of a poor quality because of insufficient

browning and lower crumb elasticity. In addition,

the amount of thermolabile vitamins, such as ribo-

flavin (B

) and thiamine (B

), is smaller.

Defect of Baking

0030It is very important to control the temperature of the

oven and the injection of steam. The main defects

during baking are due to insufficient or excessive

heat, and insufficient or excess steam. Insufficient

heat affects the quality of the bread, giving an excess

of volume, a rough crumb, thick, uncolored crust,

and an excessive loss of weight. Excessive heat pro-

duces bread with little volume, a dark crust with

bubbles, nonuniform crumb and an underbaked ap-

pearance. Insufficient steam leads to cavities between

the crumb and crust. Excessive steam produces a crust

that is too soft and has white bubbles.

0031In conclusion, the effects of baking are as follows:

an increase in the volume of bread, the formation

of crumb and crust, the decrease of thermolabile

vitamins, and the development of flavor and color.

See also: Bread: Dough Mixing and Testing Operations;

Breadmaking Processes; Dough Fermentation;

Browning: Nonenzymatic; Carbohydrates: Metabolism

of Sugars; Enzymes: Uses in Food Processing; Flour:

Analysis of Wheat Flours; Protein: Chemistry;

Interactions and Reactions Involved in Food Processing;

Starch: Structure, Properties, and Determination;

Functional Properties; Wheat: Grain Structure of Wheat

and Wheat-based Products

Further Reading

Cauvain SP and Young LS (1998) Technology of Breadmak-

ing, 1st edn. London: Blackie Academic & Professional.

Hoseney RC (1994) Principles of Cereal Science and Tech-

nology, 2nd edn. St. Paul, MN: American Association of

Cereal Chemists.

Kent N and Evers AD (1994) Technology of Cereals: An

Introduction for Students of Food Science and Agricul-

ture, 4th edn. Oxford: Pergamon.

Kulp K and Ponte JG (2000) Handbook of Cereal Science

and Technology, 2nd edn, revised and expanded. New

York: Marcel Dekker.

Lorenz KJ and Kulp K (1991) Handbook of Cereal Science

and Technology. New York: Marcel Dekker.

Oura E, Suomalainen H and Viskari R (1982) Breadmak-

ing. In: Rose AH (ed.) Economic Microbiology. Vol. 7:

Fermented Foods, pp. 87–146. London: Academic Press.

Pomeranz Y (1987) Modern Cereal Science and Technol-

ogy. New York: VCH.

Pomeranz Y (1988) Wheat: Chemistry and Technology,

3rd edn. St. Paul, MN: American Association of Cereal

Chemists.

BREAD/Chemistry of Baking 637

Quaglia G (1992) Scienza e tecnologia della panificazione.

Pinerolo: Chiriotti Editori.

Rehm HJ and Reed G (1983) Baked goods. In: Biotechnol-

ogy: A Comprehensive Treatise, Vol. 5: Food and Feed

Production with Microorganisms, pp. 1–83. Weinheim:

Verlag Chimie.

Sourdough Bread

B J B Wood, University of Strathclyde, Glasgow, UK

Background

0001 Sourdough breads, although their consumption is

lower than that of yeasted breads in developed

countries, probably predate the latter products. This

review examines the history, microbiology, and nutri-

tional significance of sourdough breads. Outlines of

some typical production processes are also provided,

but the reader is referred to the sources cited in the

Further Reading section for detailed accounts of sour-

dough bread manufacture.

0002 Sourdoughs are so called because the bread is

leavened with a mixture of yeast(s) and lactic acid

bacteria. It should be appreciated that a conventional

yeast leaven will always contain some lactic acid

bacteria, and that there will be a contribution to the

final flavor that is attributable to them, but this will

be minor and certainly will not result in a significant

acid taste in the final bread. In a true sourdough,

however, the contribution of the lactic acid bacteria

will always be detectable, at least to the experienced

palate, and quite often, the acidity is sufficient to be

noticeable to the normal consumer. The sourdough

way of making bread is of great antiquity, and many

experts would agree that it is almost certainly the

oldest way of leavening doughs, as a sour leaven will

arise naturally from organisms already present in the

flour if a mixture of flour and water is left in a warm

place for a few hours; if this is used to inoculate a

fresh flour/water mixture (dough), which is then

allowed to ferment and a portion of it is used to

inoculate a third portion of dough, and so forth,

there will be a gradual evolution of a compatible

mixture of yeast and Lactobacillus species. This type

of continuing re-inoculation has much in common

with maintaining liquid inocula by the process some-

times referred to as ‘backslopping.’ From the first

mixing of flour and water, the developed sour ferment

can be used to leaven a batch of bread dough, but as

the sour is developed through succeeding generations,

its quality and the consistency with which it leavens

bread dough will improve, and the resulting bread

will be more uniform and predictable in its quality,

other things, such as flour quality, being equal. In

some traditions, the sour dough starter is thus main-

tained for a very long time, possibly centuries, whereas

in other practices, the sour starter is begun again

every so often.

Historical Background

0003Many people, especially in the USA, think first, or

only, of the San Francisco area when sourdough

breads are mentioned. These bakers trace their roots

back to the days of the pioneers, when sourdough

bread, pancakes, etc. were an essential part of life in

the covered wagon trains. The same heritage is found

in Alaska, where the pioneers and especially the gold-

miners were called ‘sourdoughs,’ as any reader of

Jack London’s stories and Robert Service’s poems

will know. Indeed, the latter called one of his poem

collections Songs of a Sourdough. Dried yeast was not

available at that time, so sourdough was the only way

to have bread and other biologically leavened foods

on the trail or in remote encampments.

0004This way of making bread, pancakes, and other

foods would not have seemed particularly strange in

those days as many of the settlers would know, or

have kinship with, Europeans with traditions of

making this type of bread.

0005This type of baking is still very widespread in Ger-

many, Scandinavia, Eastern Europe, etc., but, perhaps

surprisingly, French breads also quite often use this

type of leaven. Even in Scotland, there was a trad-

itional way of making bread using a liquid leaven

called a ‘Parisian barm,’ which was still practised in

some areas until quite well into the twentieth century,

and one commerical bakery was still using a combin-

ation of Parisian barm and a final leavening with

pressed yeast until a few years ago.

Allied Products

0006Many foods with a relationship to sourdough breads

are produced in various parts of the world. Surplus

barm is used in making soups, e.g., Kvass is a sharp,

refreshing acidic drink found in Russia and much of

Eastern Europe and is traditionally made by toasting

or rusking sourdough rye bread, crumbling it into

water, then allowing a fermentation to take place,

after which the golden-brown, sharp, slightly spark-

ling, rather nutty-tasting liquid is poured off and

drunk. The brew is kept going by replenishing the

mixture with fresh toast and water at intervals, but

if a brew is to be started de novo, fermentation is

assured by inoculating with a portion of sourdough.

638 BREAD/Sourdough Bread

The Italian festive cake called ‘panettone’ is properly

made with a sourdough starter especially maintained

for this purpose by regular re-inoculation into a basic

panettone dough, and there are reputed to be a

number of similar products in various parts of the

world. There is also a link with products such as the

Indian food called ‘Idli,’ although it is a little tenuous,

as Idli is made from a mixture of black gram (a variety

of mung bean) and rice, and the leavening action is

due to gas produced by the heterofermentative lactic

acid bacterium Leuconostoc. Another variation is

found in the use of presoaking to prepare certain

ingredients for use in specialist breads. In a particular

case, a Scottish bakery was using whole and kibbled

(i.e., coarsely ground, crushed into large pieces or

bruised) grains in breads such as the Vogel formula

loaf and Turkestan-style bread. The whole and

kibbled grains and coarse bran were mixed with

water then left in the bakery overnight to soak up

all the water that they could. The next morning, this

mixture was incorporated with the other ingredients

to make the final dough, which was leavened with

pressed yeast in the usual manner. The bakery had not

appreciated that the overnight soaking in the warm

environment of the bakery was having any particular

effect. They assumed that the only purpose of it was

that which they had originally intended, namely to

insure that the materials in question had imbibed all

the water that they could. However, the bakery

workers had noticed that the vessels containing the

materials had a sour aroma and a marked frothiness

when uncovered in the morning. In fact, there was

a vigorous growth of lactic acid bacteria and some

wild yeasts in the mixture overnight, and the acidity

carried through to the finished bread, where it made

an appreciable contribution to the flavor of the

product.

Effects of Sour Fermentation on the Bread

0007 Several effects are observed in addition to the obvious

effect of an acid note to the flavor. The dough pro-

teins are particularly affected, with changes in elasti-

city and extensibility that may result in the dough

becoming in effect stronger, thus improving the

baking performance of weak flours, and it is thus

clear why sourdough formulations are so often asso-

ciated with rye breads, as rye flour is much weaker

than the typical wheat flour. Rye flour also differs

from wheat flour in that it possesses higher levels of

a-amylase, so that if a rye-based dough is fermented

at neutral pH, excessive breakdown of the starch is

observed. At the lower pH associated with the sour

dough process, the amylolytic activity is reduced to an

acceptable level.

0008Sourdough fermentations result in an increased hy-

drolysis of phytate from the grain; two factors are

probably at work here, the fact that these are rather

slow fermentations, so allowing more time for the

seeds’ phytases to effect hydrolysis, plus the lower

pH, which is optimal for phytase activity. There is

evidence for both phytase and phosphatase activity in

lactic acid bacteria isolated from such ferments (espe-

cially those from the ‘pre-soaks’ described in the pre-

vious section). However, the significance of the results

or the contribution that such activities (if confirmed

by more detailed work) may make to the finished

bread has not yet been established. The dietary sig-

nificance of phytase activity is that phytic acid is a

powerful chelating agent for a number of nutrition-

ally important metal ions, including calcium, copper,

iron, and zinc. Therefore, reducing the level of phytic

acid will aid the absorption of these nutrients by the

bread’s consumer, which may be particularly import-

ant to those on vegetarian and ‘macrobiotic’ diets,

although some authorities suggest that even the sup-

posedly over-fed US consumer may not be consuming

enough of these nutrients and may even be nutrition-

ally compromised for them. The six phosphate resi-

dues that are present in each molecule of phytic acid

and the inositol molecule are also made available to

the consumer of the bread only upon hydrolysis of the

phytic acid.

0009The acids formed in the fermentation are princi-

pally lactic and acetic (ethanoic) acids, and it is

believed that their presence may contribute to the

storage life of the bread by acting as mild antimicro-

bials, particularly effective against molds, which are

often the first agents of biodegradation of bread.

There is also evidence that the acids are damaging to

the spores of Bacillus species, bacteria often present

in the ingredients used for breads, particularly the

wholegrain and so-called ‘organic’ types of materials

favored by some makers of sourdough breads, be-

cause of their association with particular lifestyles.

There is also good evidence that the acidity and pos-

sibly other factors associated with sourdough fermen-

tations increase the time between baking and the

onset of evident staling of the loaf.

Sourdough Bread Processes

0010From the foregoing, it is clear that there are many

variations on the theme of sourdough bread produc-

tion, but in order to keep this discussion within rea-

sonable bounds, it is convenient to present two basic

types, bearing in mind that other approaches are not

necessarily just variants on the processes described

here, as many of them have a quite clear identity,

e.g., the Scottish ‘Parisian barm’ process mentioned

BREAD/Sourdough Bread 639

above. However, the majority of the sourdough bread

produced commercially can be legitimately regarded

as variants on one or other of the two main types.

Rye Breads (Particularly in Germany)

0011 The work of the Detmold (Germany) group of Spi-

cher and colleagues over many years has provided a

deep understanding of the sourdough breads of Ger-

many. They report that several microbial species par-

ticipate in the fermentations. From some sources, it

seems to be the practice to restart the German sour

ferments fairly frequently, and this probably helps to

bring about the diversity of species. However, Spicher

notes that ‘The development of commercial sour-

dough starter cultures over several decades has led

to a certain natural selection of organisms that pre-

dominate in the fermentation.’ This observation is in

agreement with the work of other investigators who

have studied sourdoughs from various parts of the

world. Spicher also reports that attempts to replace

these natural associations of organisms with pure

cultures, as has been done with success in the produc-

tion of commercial pressed yeast for the baking indus-

try, has not been possible. An opposite claim will be

discussed later.

0012 Among the processes in German practice according

to Spicher are multistage, two-stage, and single-stage

sourdoughs. The last require the addition of yeast for

good leavening, whereas the two-stage and multistage

processes develop a yeast flora sufficient to leaven the

dough fully. The single-stage processes are classified

into the Detmold, Berlin, and Manheim (salt-sour)

methods. In the Detmold process, the amount of

starter and the temperature used for the fermentation

are such that the process takes about 15–24 h. The

temperature is in the range of 20–28



C, with the

amount of starter (as a proportion of the sourdough)

ranging from 2% at 27–28



C to 30% at 20–23



The sourdough is made from a mixture of 55.6% rye

flour and 44.4% water. When acidification is com-

plete, this sourdough is blended with a mixture of

wheat and rye flours and water plus the necessary

yeast. Spicher quotes a typical mixture as 49.5 kg of

sourdough, 42.5 kg of rye flour, 30.0 kg of wheat

flour, and 46.0 l of water, giving a final proportion

of 70% rye flour to 30% wheat flour. In the Berlin

process, the combination of a high temperature and a

high addition of seed sour, plus a softer mixture, gives

adequate acidification in only 3–4 h. Spicher quotes a

typical mix for the souring stage of the Berlin process

as 8.0 kg of seed sour, 40.0 kg of rye flour, and 36.0 l

of water, giving a proportion of 52.6% flour to

47.4% water. The sourdough is mixed with 30.0 kg

of rye flour, 30.0 kg of wheat flour and 32.0 l of water,

again giving a final ratio of 7:3 for rye to wheat flour.

In the salt-sour process, the fermentation to produce

the sourdough is longer than in the preceding pro-

cesses, about 48 h being typical, although the pres-

ence of the salt will permit times up to 80 h to be used

without loss of quality. The mixture for the souring

stage contains 5.0 kg of seed sour, 25.0 kg of rye flour,

and 25.0 l of water, plus 500 g salt, and is fermented

at an initial temperature of 30–35



C, dropping to

15–20



C during 48 h of fermentation. This dough is

mixed with 45.0 kg of rye flour, 30.0 kg of wheat

flour, and 43.0 l of water to give the final 7:3 ratio

of rye to wheat flour. Because of the inhibitory effects

of the salt, it is necessary to add 2.5–3.5% w/w of

compressed yeast to the final dough mixture, as com-

pared with the 1.0–1.5% used with the preceding

processes.

0013In some other processes described by Spicher, and

referred to above as multistage and two-stage, the

sour is increased in volume by successive inoculation

of larger mixes of rye flour and water, each stage used

to inoculate the next. The processes seem to be rather

more favorable to the growth of desirable types of

wild yeast alongside the lactic acid bacteria (LAB),

with the result that either less compressed yeast is

added than in the single-stage processes or no added

yeast at all is needed in some of the multistage pro-

cesses.

0014In these multispecies fermentations, the major

LAB, according to a number of authors, are Lactoba-

cillus plantarum (homofermentative), L. brevis, and

L. fermentum (both heterofermentative). From the

hexose sugars available for fermentation, homofer-

mentative bacteria produce lactic acid only, or to

such an overwhelming extent that other fermentation

products are negligible in practice. Heterofermenters

produce a mixture of products, including lactic and

acetic acids, ethanol, and carbon dioxide, the ratios

of these products being influenced by various envir-

onmental factors. Other products exist of course,

and some of these play a part in the flavors that

are characteristic of lactic-fermented products. In

addition, LAB can utilize various pentose sugars,

with the production of equimolar amounts of lactic

and acetic acids. However, it is the homo- or hetero-

fermentative aspect of the fermentation that is

important here. According to previous reports, the

best-quality bread results when the three species of

bacteria are all present. The heterofermenters are

essential for development of the ‘typical flavor of

sour rye bread.’ However, the use of the heterofer-

menters alone gives a bread whose crumb lacks elas-

ticity, but inclusion of the homofermentative L.

plantarum restores this desirable attribute. The latter

organism on its own gives the desired crumb charac-

teristics, but the bread lacks aroma. Thus, both types

640 BREAD/Sourdough Bread

of organisms are essential for production of the finest

quality of bread.

0015 Spicher and coworkers have reported that the

yeasts found in sourdoughs used in the production

of rye breads fall into four types: Candida krusei,

Saccharomyces cerevisiae, S. exiguus, and Pichia sai-

toi. Again, the environmental conditions influence the

distribution of yeast species in doughs. Interactions

between the yeasts and LAB are complex, and they

can stimulate, inhibit, or have no obvious influence,

one upon another.

0016 A previous study of a sourdough started spontan-

eously on Swedish rye meal obtained a rather differ-

ent result, with some similarities to the flora of the

wheat sourdoughs (to be discussed below) in that the

fermentation came to be dominated by only one

species of yeast, although in association with three

principal LAB isolates. The yeast was identified as

Saccharomyces delbrueckii. The identities of the

LAB were less certain, except that of Pediococcus

pentosaceus; the other two dominant isolates were

assigned as Lactobacillus sp. I and sp. II (probably

L. alimentarius).

Wheat Sourdough Breads

0017 The most important study of these products is that

done on the San Francisco process by a group of

workers from the US Department of Agriculture’s

Western Regional Research Laboratories, including

Kline, Sugihara, Miller, and McCready. They reported

that the fermentation is dominated by just two micro-

organisms, Lactobacillus sanfrancisco and the yeast

Saccharomyces exiguus (sometimes referred to as

Torulopsis holmii), now reclassified as the new

species Candida milleri. Thus, both of the dominant

organisms are types first isolated from this fermenta-

tion, although both have since been reported from

other bread fermentations and also from other types

of fermentation.

0018 The most striking aspect of these studies is that the

workers have been able to offer an explanation for

the remarkable stability of the fermentation, charac-

terized by a constant ratio of yeast to LAB cells of

1:100. The yeast, unlike the usual compressed baker’s

yeast (S. cerevisiae), cannot utilize maltose, whereas

the LAB can utilize only this sugar, so they live in

harmony because they do not compete for food.

Indeed, they appear to have a symbiosis, as the LAB

utilizes maltose by the phosphorolytic route, thus

discarding one glucose molecule for every maltose

used; the yeast assimilates the glucose, and there is

evidence to suggest that the yeast liberates com-

pounds that are stimulatory, or even essential, for

the growth of the LAB, which is known to be excep-

tionally fastidious in its nutritional requirements.

Growth of the LAB has been shown to be strongly

stimulated by a small peptide, which is present in

freshly prepared yeast extract, and also to be some-

what stimulated by various minerals and vitamins

present in the extract. The yeast also has the unusual

property that it is exceptionally resistant to the anti-

biotic cycloheximide, which is used in media for

enumerating LAB because of its ability to completely

inhibit the growth of most yeasts. In collaborative

studies of Polish bakeries with scientists at the Poli-

technika Lodzka and in an examination of a Polish-

Jewish bakery in Glasgow, the presence of yeasts and

LAB with characteristics similar to those described

above has been demonstrated, and Magdalena Wlo-

darczyk has independently discovered the biochem-

ical basis of the important symbiosis between the

yeast and the LAB.

0019In the San Francisco process, the starter is routinely

rebuilt every 8 h, although it can be stored in the

refrigerator for several days without any evident de-

terioration. According to Sugihara, the rebuilding is

done by mixing 100 parts of developed sponge with

100 parts of high-gluten wheat flour and 46–52 parts

of water (all by weight). During incubation, the pH of

this mixture, initially 4.4–4.5, decreases to a final

value of 3.8–3.9. To make bread, 20 parts of this

starter sponge are mixed with 100 parts of what in

the USA is called regular patent wheat flour, 60

parts of water and two parts salt. From an initial

pH of 5.2–5.3, the value drops during 7 h of

proofing to a final value of 3.9, when it is ready for

baking.

Pure Cultures in Sourdough Bread-making

0020Sugihara reports a French study in which pure cul-

tures of a yeast (Candida tropicalis) and a LAB

(L. plantarum) were inoculated into a mixture of

one part of wheat flour and 10 parts of water plus

nutrients, with equal numbers of each organism, then

incubated at 30



C for 17 h, when the count of each

organism had increased 100-fold. This was then used

as an inoculum for breadmaking. Polish work has

demonstrated that separately cultured C. milleri

and L. sanfrancisco can be mixed in the bakery and

used for the production of a starter, which is reported

to give results superior in flavor, general quality,

and consistent production characteristics to those

obtained with their conventional starters; this tech-

nology is now being applied, together with improved

designs of equipment for developing the sour, in

bakeries in Lodz. These results are in marked contrast

with the claims reported earlier in this review that

pure cultures were not satisfactory for production of

sourdough breads; this difference may relate to the

type of bread that is being produced.

BREAD/Sourdough Bread 641

0021 The Danish company, Chr. Hansen’s Laboratorium

A/S, is now offering a selection of freeze-dried starter

cultures under the brand name ‘Florapan.’ Florapan

L-22 is Lactobacillus delbrueckii, a homofermenta-

tive strain reported to give a ‘mild and pleasant

flavor’ to the bread in which it is used. L-73 is also

homofermentative (L. plantarum) but is reported to

give the bread a ‘piquant, spicy flavour.’ Finally, L-62,

the heterofermentative L. brevis, gives a ‘penetrating

but rounded taste and a long shelf-life of the bread.’

The bacteria are particularly recommended for

whole-grain flours because of their requirements for

vitamins and minerals. The company advises that a

freshly inoculated dough be allowed to sour overnight

before use, but that where a fully developed dough is

added to a fresh dough at a ratio of up to 1:20, 8 h of

development can be sufficient. The developed dough

is then used at about 30–40% of the final mixture,

which includes baker’s yeast. Their literature makes

no comments on the crumb texture of the breads

produced with the different bacteria, although it

should be noted that the German workers attached

significance to this aspect, concluding that for the

best combination of texture and flavor, it is necessary

to use a mixture of homo- and heterofermentative

bacteria. As far as can be determined, no biochemical

or other reason has been advanced for the claimed

texture differences, so there would seem to be some

scope for some useful research here.

0022 A combination of technical advances in our under-

standing of, and capacity to control, sourdough fer-

mentations has made these processes more reliable on

a commercial production scale. At the same time, an

increased public interest in the more traditional and

‘ethnic’ types of foods has created an increasing

demand for these breads. The development of

small bakeries of the type often referred to as ‘craft’

or ‘artisan’ bakers, has contributed to this process.

Further improvements in processes, products, and

marketing strategies are possible and can further

increase the market penetration of these bread

types.

See also: Bacillus: Occurrence; Lactic Acid Bacteria;

Leavening Agents; Macrobiotic Diets; Organically

Farmed Food; Phytic Acid: Properties and

Determination; Rye; Starter Cultures; Vegetarian Diets;

Yeasts

Further Reading

Hammes WP and Ga

nzle MG (1998) Sourdough breads

and related products. In: Wood BJB (ed.) Microbiology

of Fermented Foods, 2nd edn. vol. 1, pp. 199–216.

London: Blackie Academic & Professional.

Jenson I (1998) Bread and baker’s yeast. In: Wood BJB (ed.)

Microbiology of Fermented Foods, 2nd edn. vol. 1, pp.

172–198. London: Blackie Academic & Professional.

Kent NL (1983) Technology of Cereals, 3rd edn. Oxford:

Pergamon Press.

Lonner C, Welander T, Molin N, Dostalek M and Blickstad

E (1986) The microflora in a sourdough started spon-

taneously on typical Swedish rye meal. Food Micro-

biology 3: 3–12.

Oura E, Suomalainen H and Viskari R (1982) Breadmak-

ing. In: Rose AH (ed.) Economic Microbiology, Vol. 7.

Fermented Foods, pp. 88–147. London: Academic Press.

Rocha JM and Malcata FX (1999) On the microbiological

profile of traditional Portuguese sourdough. Journal of

Food Protection 62: 1416–1429.

Service R (1957) Songs of a Sourdough. London: Ernest

Benn.

Spicher G and Pomeranz V (1985) Bread and other baked

products. In: Ullmann’s Encyclopedia of Industrial

Chemistry, 5th edn, vol. A4, pp. 331–389. Weinheim:

VCH Verlagsgesellshaft.

Steinkraus KH (1983) Handbook of Indigenous Fermented

Foods, pp. 1131–1188. New York: Marcel Dekker.

Sugihara TF (1985) Microbiology of breadmaking. In:

Wood BJB (ed.) Microbiology of Fermented Foods, vol.

1, pp. 249–262. London: Elsevier.

Wlodarczyk M (1985) Associated cultures of lactic acid

bacteria and yeasts in the industrial production of

bread. Acta Alimentaria Polonica 11: 345–359.

Wlodarczyk M (1986) Characteristic of yeasts from spon-

taneously fermenting bread starters. Acta Alimentaria

Polonica 12: 103–108.

Wood BJB, Cardenas OS, Yong FM and McNulty DW

(1975) Lactobacilli in the production of soy sauce, sour

dough and Parisian barm. In: Carr JG, Cutting CV and

Whiting GC (eds.) Lactic Acid Bacteria in Beverages and

Food, pp. 325–335. London: Academic Press.

Dietary Importance

D A T Southgate, Norwich, Norfolk, UK

The History of Bread

0001Bread has played such a key role in the human diet

that ‘bread’ is often taken as being synonymous with

food as a whole, and in some dialects, it is used as a

slang term for money, the means of obtaining food.

Bread indeed has a very long history of use in the

human diet.

0002The cultivation of cereals, especially wheat,

appears to have started in the Middle East, and along-

side the evidence for the cultivation of wheat, one

finds evidence of loaves apparently produced with

642 BREAD/Dietary Importance

yeast, and baked in ovens. Wheat is the primary

cereal for producing bread, although in Northern

Europe at the northern limit of cultivation for

wheat, rye is widely used in breads, and wheat/rye

mixtures are widely consumed. Earlier archeological

evidence provides artefacts in the form of querns used

for grinding cereal grains mainly barley, which was

usually eaten as solid cakes.

0003 Wheat as a cereal has the special compositional

property that when ground grains are mixed with

water and yeast, the fermentation of the starch pro-

duces a very attractive type of food. There are many

references to leavened and unleavened breads in the

Old Testament, and the Greeks and Romans both

produced breads analogous to those consumed

today. The cultivation of wheat provided an abun-

dant source of food energy, together with a protein

level and a protein with a balanced amino acid com-

position that made it a very nutritious food. In add-

ition, the wheat grains could be stored from one

harvest to the next and, if necessary, for longer

periods to cover periods when crops failed. This led

to wheaten bread becoming an important staple food.

There is clear evidence of the importance of bread in

the diet of both the Greeks and the Romans. The

milling of wheat grains in querns and wind- or

water-powered millstones exerts a shearing force on

the grain separating a flake of the outer branny layers

while progressively breaking the endosperm into

smaller fragments and eventually flour. The bran

and flour can be separated by sieving to produce a

white flour, which, from earliest times, was used to

produce a more prestigious food. Both the Greeks and

the Romans argued about the merits of white versus

wholemeal breads, a debate that continues to the

present time.

0004 In medieval times, wheaten bread was extremely

important in the diet of the poorer classes, and a

system of rigorous price control was developed to

ensure that the peasants were kept supplied with

ample bread. Severe penalties were also implemented

to prevent the bread being adulterated with inferior

foods such as pulses. In the UK, the price of bread has

continued to be seen as extremely important by suc-

cessive governments, as a means of keeping the people

well fed and contented. To a certain extent, bread has

become a ‘token food’ with regulations as to the size

of loaves, the price of loaves, and permitted ingredi-

ents and additives. During both world wars, the

extraction rate of bread flour was controlled at a

high level to reduce shipping requirements, and in

World War II, fortification with calcium and, later,

iron and some vitamins was obligatory to maintain

the nutritional value of the diet, with bread being

used as a vehicle. Recently, proposals have been

made to fortify bread with folic acid, to prevent

neural-tube defects, and vitamin D, to ensure that

Asian immigrants to the UK obtain this vitamin

from their wholemeal chapatis.

0005Thus, since it first became part of the human diet,

wheat and the breads made from it have provided an

important staple food, and, despite the growth of

affluence and the wider variety of foods available to

most developed populations, it remains an important

and nutritious food. Most current dietary advice

regarding healthy eating advocates the consumption

of a substantial amount of cereal foods in the diet,

and this of course includes breads. The recognition of

the role of dietary fiber in the diet has emphasized the

importance of wholemeal and higher extraction

breads, but most advice returns to the theme that

all breads are good foods.

Nutritional Composition of Bread

0006Although much of the focus of this article will be on

wheaten bread, some information on rye breads has

also been included because these are also widely

consumed, and in the UK, mixed grain breads have

achieved some popularity. The focus on breads has

been limited to those breads prepared by fermenta-

tion of the dough with yeast, although many commu-

nities consider many nonfermented rye products as

breads.

Bread Production

0007Wheat and, to a lesser extent, rye and barley proteins

contain gluten, which, as the dough is kneaded

(or developed mechanically) forms a network within

the dough that traps the carbon dioxide produced by

fermentation of the carbohydrates in the flour by the

yeast. This causes the dough to rise and leads to

the development of the crumb texture when the

dough is baked. The increased volume of the bread

is an important factor in the sensory quality of bread

and is possibly why breads have become established

in the diet. Baking produces a crust that contains

some starch granules that are not fully gelatinized

and, in well-baked bread, can produce starch degrad-

ation products and even some carbon. These modified

carbohydrates in the crust are important for the sens-

ory characteristics of bread, but do not materially

affect the nutritional value. Some salt is usually

added to the dough to assist in the activation of the

yeast, and other ‘flour improvers’ are added to facili-

tate the development of cross-linking in the gluten

and so strengthen the network. Vitamin C is the

only permitted improver in wholemeal bread in

the UK, but the baking process effectively destroys

any residual vitamin.

BREAD/Dietary Importance 643

Composition of Wheaten Breads

0008 The composition of some typical wheaten breads is

given in Table 1 with a range taken from British,

Italian, and Danish Food Composition tables to illus-

trate values from southern and northern Europe. It

should be stressed that there is some variation in

composition; the protein content, for example,

depends very much on the selection of wheat mixture

chosen by the bakers. The majority of home-grown

wheats in the UK are soft, lower-protein wheats and

need to be mixed with harder, high-protein wheats,

typically from North America. Table 1 illustrates the

difference that the inclusion of the bran makes, with

the wholemeal breads typically containing two to

three times as much dietary fiber (the values cited

are for nonstarch polysaccharides). In most bread

mixes, a small quantity of fat, usually as oil, is incorp-

orated into the mix. In Denmark, there is a preference

for softer crumbs, and the fat levels are higher. In the

USA, milk powder may be included to produce simi-

lar softer crumbs. The levels of fat in Italian white

bread are very low and probably represent an anom-

aly due to the choice of method for fat. Most of the

carbohydrate is starch, with small amounts of free

sugars and dextrins in the crust.

0009 The water contents vary with the extent of staling,

but the Italians seem to prefer a drier white bread.

Table 2 lists the corresponding values for several

inorganic constituents. The sodium contents are sub-

stantial, and bread is an important source of sodium

in the diet. Recently, there have been moves within

the bread producers to lower the levels as a public

health measure. Salt plays an important role in bread

flavor, in addition to activating the yeast, so reduc-

tions will have to be phased in.

0010The wholemeal breads have higher potassium,

phosphorus, iron, and zinc levels, representing the

higher concentrations of these elements in the outer

layers of the grain. Incorporation of the germ in the

bread also increases the levels over the values for

white bread. The UK data for calcium and iron are

higher than in other countries because of fortification

of all flours except wholemeal.

0011Table 3 lists values for a number of vitamins.

The concentration of most B vitamins is higher in the

outer layers of the grain, so the values for the whole-

meal breads are higher, except for folate in Danish

breads. The thiamin and niacin values in the British

breads represent the effects of fortification.

Rye Breads

0012Table 4 lists the compositions of several rye breads

taken from the British and Danish food composition

tables. This shows that rye breads fermented with

yeast are very similar in overall composition to

wheaten breads. The Danish appear to prefer a

tbl0001 Table 1 Major constituents of wheaten breads (per 100 g)

Bread type Water (g) Protein (g) Fat (g) Carbohydrate(g) Dietary fiber (gnonstarch

polysaccharides)

Energy (kJ) Countryof origin

Wholemeal 38.3 9.2 2.5 41.6 5.8 914 UK

Brown 39.5 8.5 2.0 44.3 3.5 927 UK

Wheatgerm 40.3 9.5 2.0 41.5 3.3 899 UK

White 37.3 8.4 1.9 49.3 1.5 1002 UK

Wholemeal 38.4 8.2 2.0 49.3 5.3 1054 Denmark

White 37.9 7.2 3.2 49.9 3.9 1092 Denmark

Wholemeal

36.6 7.5 1.3 53.8 5.7 1017 Italy

White

29.0 8.1 0.2 64.7 2.8 1167 Italy

Pane integrale.

Pane commune.

tbl0002 Table 2 Major inorganic constituents of wheaten bread (per 100 g)

Bread type Sodium (mg) Potassium (mg) Calcium (mg) Magnesium (mg) Phosphorus (mg) Iron (mg) Zinc (mg) Countryof origin

Wholemeal 550 230 54 76 200 2.7 1.8 UK

Brown 540 170 100 53 150 2.2 1.1 UK

Wheatgerm 600 200 120 56 190 3.7 2.1 UK

White 520 110 110 24 91 1.6 0.6 UK

Wholemeal 511 198 49 39 268 1.65 1.25 Denmark

White 453 136 44 20 128 1.19 0.65 Denmark

Wholemeal 550 210 25 180 2.5 1.6 Italy

White 665 161 64 100 1.7 0.8 Italy

644 BREAD/Dietary Importance