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

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slightly higher moisture content, which reflects the

higher water-binding activity of the carbohydrates

in rye. The rye breads tend to contain higher amounts

of dietary fiber, and this has a higher proportion of

soluble nonstarch polysaccharides than wheat. Rye

grains have a different structure to wheat, and the

bran is less easily separated from the endosperm, so

the light rye bread is of a higher extraction than white

wheaten breads.

0013 The wider range of rye breads cited in the Danish

tables is typical of northern Europe, where rye breads

and rye/wheaten mixtures are widely consumed. Rye

proteins contain gluten levels that are less effective in

increasing the volume of the bread, and the inclusion

of a proportion of wheat is widely practiced in

Germany and Scandinavia.

Nutritional Significance of Bread in the

Diet

0014 This derives both from the quantitative nutritional

contribution of breads in the diet and from the quali-

tative characteristics of the components of both

wheat and rye grains.

Qualitative Aspects

0015 Protein Breads are often seen as important in

the provision of carbohydrates, and consequentially

as a source of energy, and over the past 30 years as a

source of dietary fiber. This limited view of breads as

carbohydrate foods is misleading because their pro-

teins are important nutritionally. White bread con-

tains 8.4 g per 1002 kJ (235 kcal), so the protein:

energy ratio is well above that considered nutrition-

ally essential. Protein– energy malnutrition is virtu-

ally unknown amongst populations where wheat is

the stable cereal. The amino acid compositions of

both wheat and rye proteins are reasonably well bal-

anced with the sulfur-amino acids being limiting, so a

combination of bread and vegetables provides a very

good combination. Baking results in a small reduc-

tion in the available lysine content but still retains the

overall protein quality.

0016Carbohydrates The major carbohydrate in bread is

starch, with relatively minor amounts of free sugars.

Some degradation of the starch occurs in the crust

during baking, producing soluble dextrins and some

Maillard reaction products. The production of bread

leads to the formation of some retrograded starch,

which is physiologically resistant to digestion in the

small intestine. The resistant starch is formed from

the amylose portion of the starch that combines to

form insoluble crystalline products. The proportion

of ‘resistant starch’ increases with staling of the

bread. The bulk of the starch, however, in breads,

especially white bread, is rapidly digestible and is

responsible for the high glycemic index of white

bread.

0017The dietary fiber in wheat comes principally from

two sources: the outer branny layers contain cellulose

and noncellulosic polysaccharides. Wheat and rye

bran noncellulosic polysaccharides are both rich in

arabino-xylans, which are important in the water-

binding properties of the flour. The bran layers are

lignified and resistant to bacterial degradation in

tbl0004 Table 4 Composition of some rye breads (per 100 g)

Type of bread Water (g) Protein

(g)

Fat (g) Carbo-

hydrate (g)

Dietary

fiber (g)

Na (mg) K (mg) P (mg) Fe (mg) Thiamin

(mg)

Niacin

(mg)

Folate

(mg)

Country of

origin

Wholemeal 37.4 8.3 1.7 45.8 5.8 580 190 160 1.0 0.29 2.3 24 UK

Dark wholemeal 41.1 6.2 1.7 48.7 8.6 573 294 266 2.28 0.19 1.1 43 Denmark

Dark 41.5 6.2 1.7 48.1 9.2 558 296 285 2.3 0.21 1.1 43 Denmark

Light 42.8 6.2 1.3 47.6 7.5 562 266 208 2.1 0.20 0.7 43 Denmark

tbl0003 Table 3 Vitamins in wheaten breads (per 100 g)

Bread type Thiamin (vitamin B

) (mg) Riboflavin (vitamin B

) (mg) Niacin (mg) Vitamin B

(mg) Folate (mg) Country of origin

Wholemeal 0.34 0.09 4.1 0.12 39 UK

Brown 0.27 0.09 2.5 0.13 40 UK

Wheatgerm 0.80 0.09 4.2 0.11 39 UK

White 0.21 0.06 1.7 0.07 29 UK

Wholemeal 0.22 0.12 2.5 0.16 49 Denmark

White 0.18 0.10 1.2 0.07 70 Denmark

Wholemeal 0.10 0.12 2.9 0.12 39 Italy

White 0.02 0.03 1.4 0.07 29 Italy

BREAD/Dietary Importance 645

the large intestine. The dietary fiber in wheat bran is

one of the more effective sources of dietary fiber for

increasing fecal bulk.

0018 The endosperm contains smaller quantities of thin-

walled cells, the walls of which are rich in cellulose

and b-glucans.

0019 Minerals and vitamins Wholewheat breads contain

significant amounts of potassium, magnesium, phos-

phorus, and iron, together with important amounts of

thiamin, niacin, and small amounts of folates. A sub-

stantial proportion of the phosphorus is present as

phytic acid, and this has been shown to reduce the

bioavailability of calcium and iron. At the start of

World War II, there was nutritional concern that the

availability of dairy products would be reduced and

that any increase of the extraction rate to conserve the

imported grain would result in reduced amounts of

calcium being available in the diet. This led to the

fortification of wheat flours with calcium carbonate.

When the extraction rate of bread was increased to

make a higher proportion of the imported wheat grain

to be used for human consumption, this also increased

the amounts of thiamin, niacin, and iron in the bread.

When, in the early 1950s, the production of white

bread was again permitted, it was decide that the

nutritional composition of all flours, except whole-

meal, should be maintained by fortification with iron,

thamin, and niacin to maintain the levels in the higher

extraction breads available during the war.

Consumption and Nutritional Contributions

0020 Since classical times, bread, especially wheaten bread,

has provided the staple source of energy and the other

nutrients it contains. This was particularly true for

the mass of the population in ancient Egypt and clas-

sical Greece and Rome. This reliance of the lower

socio-economic groups on bread as the staple source

of energy and nutrients continued through medieval

times to the early years of the 20th century in Europe.

In the UK, bread was seen as a special food, and

successive governments saw controlling the price of

bread as the key to keeping the ‘masses’ contented,

just as it was in Roman times. Even amongst the

poorer members of the community, however, there

was a preference for white ‘low-extraction’ flours

that were seen as purer and conferred some measure

of status on the consumer. This continues, despite

repeated advice from the medical and other health

professionals that higher-extraction breads are better

for health. Probably, such breads were less easily

adulterated in earlier times with cheaper beans or

barley flour.

0021The key to assessing the dietary importance lies

in considering the amounts of bread consumed

together with the composition of those breads. The

UK National Food Survey provides a continuous

record of food consumption over the last 47 years.

In its earlier years, it measured only foods purchased

to be consumed within the home, but more recently,

because the consumption of meals outside the home

has increased, the Survey has included estimates of

them.

0022During World War II, bread was not rationed and

thus provided a major source of energy. As mentioned

previously, the extraction rate of bread-making flours

was controlled to around 80–85%, resulting in a

bread that was gray/brown for most of the 1940s.

Consumption was then of the order of 1721 g per

person per week (Table 5), but when the war ended,

rationing was introduced, and consumption fell to

around 1420 g.

0023Control on flour was abolished in 1956, and con-

sumption switched very rapidly from the ‘national

loaf’ at about 80–85% extraction to white at about

1200 g, illustrating very clearly the popular prefer-

ence for white bread. Since that time, the overall

consumption of breads has shown a steady decline,

reflecting the improved economic status of the popu-

lation and the increased availability of other foods.

The National Food Survey data for the earlier years

are, however, for foods purchased for the home, and

with improving economic conditions, the consump-

tion of meals outside the home increased in import-

ance. In recent years, the growth in ‘sandwich shops’

providing bread-based meals for consumption at

midday means that the consumption of bread per se

may not have declined so extensively.

0024Table 6 lists some data for 1997 on the patterns of

bread purchases within different income groups,

tbl0005 Table 5 Changes in total bread consumption in the UK (grams per person per week)

Ye ar 19 42 1950 19 60 1970 19 9 0 19 9 0 19 97

Consumption 1721 1640 1291 1082 884 798 745

Comment War time Rationing After controls

were relaxed

From MAFF (1991) Household Food Consumption and Expenditure 1990. London: HMSO; MAFF (1998) National Food Survey 1997. London: The Stationery

Office.

646 BREAD/Dietary Importance

showing the greater consumption of bread by the

lower income groups and especially amongst those

receiving the state old age pension. This group in-

cludes those with additional pensions from employ-

ment, and the group as a whole may have a net

income above those in the lowest income group, D.

It is interesting to note the dominant position of white

bread in the lower income groups. Bread consump-

tion amongst the large families in the lower income

groups tends also to be higher, emphasizing that

bread still provides an important stable food.

Importance as a Source of Nutrients

0025 Table 7 shows the contribution of bread to the

intakes of some nutrients (per person per day) and

the percentage contribution to the total intakes.

These show that bread makes a greater contribution

to protein intakes than energy. The contribution to

fat intakes is very minor, but it must be recognized

that bread acts as a vehicle for introducing fat into the

diet via spreads and sandwich fillings. The dietary

fiber intake comes almost equally from white and

wholemeal breads because of the relative proportions

consumed. Despite fortification, bread is a minor

source of calcium in the diet, although iron fortifica-

tion means that bread is a significant iron source. The

contribution of bread to sodium intake has been a

cause of some nutritional concern and is currently

being addressed by the bread industry.

Conclusions

0026Bread, especially wheaten bread, has played an im-

portant role in the human diet ever since wheat began

to be cultivated in the Middle East. It remains an

important stable source of nutrients and energy, and

as a source of complex carbohydrates, a food whose

consumption, especially the higher-extraction types,

should be encouraged as part of a healthy diet.

See also: Protein: Food Sources; Rye; Starch: Structure,

Properties, and Determination

Further Reading

Holland B, Welch AA, Unwin ID, Buss DH, Paul AA and

Southgate DAT (1991) McCance and Widdowson’s The

Composition of Foods, 5th edn. Cambridge: Royal Soci-

ety of Chemistry and Ministry of Agriculture Fisheries

and Food.

McCance RA and Widdowson EM (1956) Breads White

and Brown: Their Place in Thought and Social History.

London: Pitman Medical Publishing.

MAFF (1991) Household Food Consumption and Expend-

iture 1990. London: HMSO.

MAFF (1998) National Food Survey 1997. London: The

Stationery Office.

Salvini S, Parpinel M, Gnagnarella P, Maisonneuve P and

Turrini A (1998) Banca Dati di Composizione per Studi

Epidemiologici in Italia. Milan: Tipografia F lli Ver-

derio.

Dough Fermentation

M Collado-Ferna

ndez, University of Burgos, Burgos,

Spain

Background

0001Fermentation involves a complex system of reactions

brought about by microorganisms that may be pre-

sent simultaneously. There are different types of fer-

mentation resulting from the action of yeast and other

microorganisms such as lactic acid bacteria. The prin-

cipal type of fermentation is the action of the yeast on

fermentable sugars to produce carbon dioxide (CO

ethanol, and some aromatic compounds.

tbl0006 Table 6 Consumption of different breads by income groups

for

UK in 1997 (grams per person per week)

Incomegroup ABCDStatepensioners

Bread type

White 312 393 461 409 458

Brown 73 68 77 95 273

Wholemeal 87 83 79 63 139

Other breads 171 156 147 104 136

Total bread 635 700 765 772 867

Income groups are based on the total household income: Group A highest

10%; Group B next 40%; Group C next 40%; Group D lowest 10% of

families with earner in family.

tbl0007 Table 7 Nutrient contributions of breads to UK intake in 1997

combined contributions of white, brown, and wholemeal) (per

person per day)

Nutrient Contribution Percentage of

totalintake

Energy (kcal) 142 7.9

Protein (g) 11.0 17.0

Fat (g) 1.2 1.5

Sugars (g) 1.6 1.3

Starch (g) 27.6 21.1

Dietary fiber (nonstarch

polysaccharides) (g)

1.8 14.5

Calcium (mg) 60 7.3

Iron (mg) 1.3 13.9

Sodium (mg) 345 13.4

BREAD/Dough Fermentation 647

0002 The organoleptic characteristics of bread, namely,

the texture, flavor, and aroma, depend on the condi-

tions of the dough fermentation.

0003 Fermentation begins when the yeast is in contact

with the dough and finishes some minutes after the

dough has been placed into the oven. There are two

phases in the fermentation: the bulk fermentation or

first fermentation or first proof and the fermentation

or final proof or proving. The bulk fermentation

tends to be substituted by intensive kneading or by

other methods.

0004 During fermentation, there must be a balance

between gas production and gas retention and the

characteristic viscoelastics of dough. The dough

undergoes several changes like weight loss, changes

in carbohydrates, and phytates.

Yeast

0005 Yeast is a living unicellular organism, has a length of

6–8 mm, and is round to oval in shape. One gram of

yeast contains around 15 10

cells. The yeast cell

has an external membrane called the cell wall. This

has a selective permeability and has an important role

in controlling (by osmotic processes) the movement

of nutrients and other substances into the cell and the

release of other substances such as CO

and ethanol.

Bakers’ yeast is Saccharomyces cerevisiae. Commer-

cial production of yeast is based on growth, on an

industrial scale, of a pure selected strain. The cell

culture obtained is separated from the culture medium

and prepared for processing. The yeast can be

compressed (most common), granular, dried in the

form of a pellet, instantaneous, encapsulated, frozen,

or in the form of a ‘cream.’ These variations

are related to the physical form of the yeast and,

mainly, the yeast moisture content. In terms of the

speed of yeast fermentation, there are two types,

standard and rapid, related to the maltose adapta-

tion. Rapid yeast is more active than standard yeast,

and is adapted for use in accelerated breadmaking

systems.

0006 Yeast is a versatile organism that can act under

aerobic and anaerobic conditions. Under aerobic con-

ditions, yeast grows quickly, owing to the oxygen-

ation of sugar, which produces new yeast, water,

and the energy needed for its growth. Under anaer-

obic conditions, yeast transforms the sugar into

carbon dioxide and ethanol by fermentation.

0007 The speed with which yeast consumes sugars and

produces CO

depends on factors such as: the yeast

strain used, resistance to osmotic pressure, maltose

adaptation, yeast concentration, flour fermentative

capacity, temperature and pH of the dough, and

presence of dough inhibitors.

Strain

0008The selection of yeast strain is a function of the fer-

mentative properties of the dough, the breadmaking

process, the high stability of its characteristics, and a

good industrial yield.

Resistance to Osmotic Pressure

0009Some strains have a high tolerance to osmotic pres-

sure, but others do not and consequently die. The

increase in osmotic pressure in the cell wall is due to

factors such as salt and sugar concentration, the in-

vertase action of the yeast itself. The decrease in water

in the formulation of the doughs that include high

levels of fat and sugar, and especially problems pre-

sented by frozen dough sugar; during freezing, the

free water decreases, and the osmotic pressure

increases.

Maltose Adaptation

0010In order to maintain a good production of gas, yeast

requires a plentiful and continuous supply of glucose

as an energy source. The action of a- and b-amylases

of flour in damaged starch gives maltose (starch

damage results from modifications in the structure

of starch during the milling process). This disacchar-

ide is transported into the cell, in which it is broken

down into two molecules of glucose. The metabolic

changes to this new source of glucose from starch are

only active when yeast detects the presence of maltose

in the medium, and its functioning takes some time

(lag phase). Consequently, the rate of gas production

decreases until this mechanism is working fully, and

then, gas production increases. The decrease in gas

production is lower as soon as the maltose adaptation

begins, which is different for rapid and standard yeast

strains. The choice of one over another depends on

the breadmaking process to be used.

Yeast concentration

0011When sugar is not added to dough, the limiting factor

of gas production is the quantity of maltose available.

The increase in yeast concentration at one tempera-

ture leads to an increase in the rate of gas production

and greater sugar depletion.

Fermentative Capacity of Flour

0012The quantity of amylase in flour determines the

degree of glucose production from starch, so long as

there is enough damaged starch.

Temperature

0013Temperature has an important influence on yeast ac-

tivity: at 4



C, there is no activity, and fermentation

648 BREAD/Dough Fermentation

does not occur, at 10–15



C, the yeast activity and

fermentation are slow, at 20–40



C, fermentation is

very active, at 45



C yeast activity slows down, and at



C, the yeast dies. Thus, the best storage tempera-

ture for yeast is 4



C(0–10



C). Depending on the

strain used, an increase of 1



C in the dough gives an

8–12% increase in fermentation speed. Although, at



C, there is more gas production, there is also

lactic and butyric fermentation (which is undesirable).

0014 Yeast is very tolerant to fluctuations in environmental

pH (2–8), but the optimum pH for yeast activity is

between 4 and 6. Usually, the pH of dough is 5,

although the pH may be lower when sourdough is

used.

0015 The undissociated forms of organic acids produced

from parallel fermentation to alcoholic fermentation,

that is, produced by lactic acid bacteria of flour and

by contamination of yeast, are inhibitors of fermen-

tative activity. They have greater effects at lower pHs,

the critical zone being between 4 and 5, and these

values correspond to the final fermentation.

Presence of Dough Inhibitors

0016 The copper and chlorine present in water used in

breadmaking processes can act as fermentation in-

hibitors. Organic acids, such as those used as preser-

vatives (acetic and propionic acid) and others formed

during fermentation, can also act as fermentation

inhibitors.

Sources of Sugar used by Yeast

0017 Yeast uses four different sources of sugar: (1) treha-

lose endogenous, (2) free sugar from flour, (3) sugars

obtained by the action of enzymes in oligosaccharides

and polysaccharides in the flour, or added as addi-

tives, and (4) added sugars such as sucrose. Fermen-

tation begins with trehalose, then later with the free

sugars and sugars added, and finally with maltose.

The hydrolysis of sucrose to glucose and fructose is

faster than the fermentation of glucose and fructose.

The consumption of glucose is greater than that of

fructose, and initially, the consumption of maltose is

low, but when most of the other sugars have been

consumed, the yeast ferments the maltose rapidly.

This also depends on the capacity of yeast to adapt

to maltose.

Carbohydrate Metabolism

0018 Yeast ferments monosaccharides – glucose (mainly),

fructose, and mannose, disaccharides – sucrose, mal-

tose, and trehalose – and trisaccharides (rafinose).

Yeast does not consume lactose. The transformation

of carbohydrates during dough fermentation is shown

in Figure 1.

0019Yeast can transform carbohydrates in different

ways: via the Embden–Meyerhof–Parnas pathway

(EMP, glycolysis) and from hexose monophosphate

(HMP). Under anaerobic conditions, the carbon

dioxide formed is by the EMP pathway, and under

aerobic conditions, the carbon dioxide may be

formed by HMP from pyruvate (via the tricarboxylic

acid (TCA) cycle or Krebs cycle). Under aerobic con-

ditions, yeast grows rapidly and accumulates a small

amount of carbon dioxide and ethanol, whereas under

anaerobic conditions, yeast grows slowly and pro-

duces a large amount of carbon dioxide and ethanol.

0020The pyruvate formed in these ways is very import-

ant as a precursor to acids, alcohol, and other volatile

compounds, which have an influence on the flavor

and aroma of bread (Figure 2).

Production and Retention of Gas

0021The quality of gluten is related to gas retention, but

also, the degree of gas retention depends on the rate of

diffusion. During kneading, air is incorporated into

the dough, and air bubbles are formed. These bubbles

contain mainly nitrogen, because it has a low solubil-

ity in water, and oxygen is quickly used up by the

yeast cells within the dough. Yeast cannot create new

bubbles, as the pressure (P) in a bubble is related to

the radius (r) of the bubble and the interfacial tension

(g) by the law of Laplace: P ¼ 2g/r. The creation of

new bubbles is only possible by punching or remixing

the dough, or by the use of surfactants that change the

interfacial tension. The more bubbles are formed, the

finer the grain is.

+ H

Starch Maltose

α-Amilase

(α-Glucosidase)

+ H

O2C

Maltose Glucose

Maltase

(β-Fructosidase)

+ H

+ C

Sucrose Glucose Fructose

Invertase

2CO

+ 2C

Glucose Ethanol

Zimase

2CO

+ 2C

Fructose Ethanol

Zimase

fig0001Figure 1 Carbohydrate transformation during dough fermenta-

tion.

BREAD/Dough Fermentation 649

0022 During kneading, yeast is mixed into the dough, and

fermentation starts. The major breakdown products

are carbon dioxide and ethanol. Initially, carbon diox-

ide is produced in the aqueous phase, the pH decreases,

and this phase becomes saturated with carbon dioxide.

As the fermentation proceeds, carbon dioxide is

retained in the air bubble, and nitrogen is displaced.

Then, the dough is leavened, because the aqueous

phase is saturated by CO

and the newly formed CO

is retained in preexisting bubbles. At this point, the

quality of gluten is also very important to retain the

gas, and thus, carbon dioxide is retained in the dough

in two phases: contained within the gas cells and dis-

solved in the aqueous phase. At the pH of dough, most

of the carbon dioxide is present as CO

and a small

amount of this as CO

2

, HCO



,orH

0023 Only 45% of the total gas produced is present at

the end of fermentation. The loss of carbon dioxide is

due to the different steps of breadmaking process,

namely initial fermentation, punching, rounding,

molding, and final fermentation.

0024 The gas-retention capacity of the gluten decreases

with time and is critical when the dough is placed into

the oven. The high temperatures expand the retained

gas and increase the volume of the dough, and so if

the gluten has a good gas-retention capacity, it will

yield bread with a good volume, otherwise the bread

will be flat. The vaporization of ethanol and water

present in the dough also contribute slightly to dough

expansion.

Fermentation

0025 There are two phases in fermentation: bulk fermenta-

tion, first fermentation, or first proof and the main

fermentation, final proof, or proving. Bulk fermenta-

tion takes place from final kneading to the dividing of

the dough. In this phase, the dough undergoes several

physical modifications that allow it to be cut and

molded. This phase tends to be substituted by inten-

sive kneading or other methods. The final proof takes

place from molding to baking, so this phase really is

the fermentation.

0026The relative lengths of time of these phases depend

on the physical properties of the dough, which

depend on the kind of wheat used: when using soft

flours that produce dough that is short and not very

elastic, the fermentation time should be reduced.

0027During fermentation, the temperature and relative

humidity need to be taken into account. The tempera-

ture used depends on the kind of bread and the

breadmaking process (usually 28–30



C), with lower

temperatures requiring longer fermentation times

(1–1.30 h or 2–4 h), but also depends on the yeast

concentration used. If the temperature is lower, the

dough will be very cold, the fermentation will be

longer, and gas production will decrease. As the

fermentation is longer, the concentration of sugar

increases, and the texture of the bread will be of a

lower quality and rough grained, and will have a

colorful crust with shorter shelf-life. If the tempera-

ture is higher, the crumb will be rougher, and non-

alcoholic fermentation may occur. If the relative

humidity is < 75%, the skin of the dough will be

very dry and will lose its elasticity.

0028During fermentation, the pH of dough changes,

principally owing to the formation of lactic acid.

Initially, dough has a pH of about 6.2, and during

fermentation, the values are about 5.76 or 5.67. This

acidic environment improves the formation of gluten,

which is more extensible, and in bread, this slows

down the growth of mold.

0029The pH of dough has a great influence on fermen-

tation, because yeast needs an acid environment (pH

5.8–6.2), and also influences the properties of protein

and the activity of enzymes.

EMP HMP

Fermentable sugars

Propanol

Propionate Lactate

Pyruvate

Ethyl acetate

Acetaldehyde + CO

Ethanol

Formate + Acetate

Acetyl-CoA

Oxaloacetate

Succcinate

Pro

ionate

Diacetyl Acetoine

2,3 butanodiol

Butanona-2

Acetyl acetate

Butyrate Acetone + Ethanol

Butanol Isopropanol

fig0002 Figure 2 Some of the breakdown products from sugar metabolism.

650 BREAD/Dough Fermentation

0030 During fermentation, dough increases the force (W,

work (related to the curve of the alveogram)) and

decreases the tenacity (P, pressure (related to the

height of the curve of the alveogram)) so the relation

P/L decreases (L being extensibility). The capacity of

dough to withstand excessive mechanical work is

called dough tolerance. Generally, doughs that fer-

ment slowly are more tolerant.

Fermentation Types

0031 Not all sugar is transformed by yeast. Lactic acid

bacteria (usually present in dough, especially in sour-

dough) carry out fermentation, consuming sugar and

producing CO

(Figure 3). The types of fermentation

are: alcoholic fermentation, lactic fermentation, bu-

tyric fermentation, and acetic fermentation.

Alcoholic Fermentation

0032 This is the principal type of fermentation. Yeast

transforms fermentable sugars, mainly glucose, into

carbon dioxide and ethanol. The optimum pH for

alcoholic fermentation of dough is 5. If the pH is

higher (> 6), the breakdown products of fermentation

are glycerine and acetic acid as well as carbon dioxide

and ethanol.

Lactic Fermentation

0033Lactic fermentation is achieved by the hydrolysis of

lactose or glucose by lactic acid bacteria, giving lactic

acid. Usually, yeast is contaminated with lactic acid

bacteria. The optimum temperature for lactic fermen-

tation is 35



C, so this fermentation is slow at the

temperature of yeast fermentation. The lactic acid

acts in the dough, giving a more elastic gluten.

Butyric Fermentation

0034Different bacteria, such as Clostridium butyricum,

may use the lactic acid to produce butyric acid. The

temperature of this reaction is about 40



C, so during

dough fermentation, these bacteria cannot act. How-

ever, if the dough has a long fermentation time, it

increases its temperature (more than 32



C), and

butyric fermentation may occur, affecting the aroma

of bread. The pH of this reaction is 3.2–3.8.

Acetic Fermentation

0035Acetic fermentation is carried out by Mycoderma

aceti, which transform the ethanol into acetic acid.

The optimum reaction for Mycoderma aceti occurs

under aerobic conditions. The contribution of acetic

acid alone to the total acidity of the dough is 5%. The

excess of acetic acid content gives short and rigid

Alcoholic fermentation

2CO

+ 2C

Glucose

Ethanol

Ethanol Acetic acid

Saccharomyces cerevisiae

+ H

O2CO

+ C

OH + C

+ 2CH

OH CHOH--CH

pH > 6

Glycerine

Lactic fermentation

+ H

O C

Lactose Glucose

Glucose Lactic acid

Lactic acid Butyric acid

Lactic-acid bacteria

+ 2CO

+ 2H

Clostridium butyricum

Butyric fermentation

Ethanol Acetic acid

OH + 2O

+ 2H

Mycoderma aceti

Acetic fermentation

fig0003 Figure 3 Types of fermentation during the breadmaking process.

BREAD/Dough Fermentation 651

gluten. Therefore, it is necessary to insure that the

ratio of lactic acid to acetic acid formed is 3/1.

Controlled Fermentation

0036 Controlled fermentation is one of the new techniques

to apply cold, to stop, or to decrease the fermenta-

tion. The possibility of controlling and programming

fermentation has the advantage in that it is possible to

regulate bread production, avoid working at night,

produce fresh bread any time, and utilize the advan-

tages of long fermentation, i.e., a better shelf-life

aroma, and flavor.

Raw Materials

0037 The flour must be of good quality (W ¼160–180;

P/L ¼0.4–0.6, falling number 300–350 s), because

the dough must not ferment before the block phase,

and flour needs less enzymatic activity than trad-

itional fermentation. Standard yeast must be used,

because the fermentation must not begin before the

block phase. The yeast concentration is usually 2–3%

(based on flour weight). Fresh sourdough is also

added in the bread mixture.

Manufacturing

0038 The kneading time required for dough development is

20% longer than the traditional breadmaking pro-

cess, because the flour is stronger. Two to 3% less

water in the formulation is recommended, to insure

that the dough is not too soft, and the final tempera-

ture of the dough should be 22



C to avoid premature

fermentation. The dough is divided, rounded, and

molded as soon as possible, and then pieces of the

dough are placed into a controlled fermentation

cabinet.

Proof Cabinets

0039 The design of the proof cabinet has evolved with

time. Traditional bakeries used wood cupboards

with large boxes to ferment the dough, and some

still use these. These proof cabinets present some

problems, because they are affected by the tempera-

ture of the workroom, and the fermentation is not the

same in all the pieces of the dough. Nowadays the

proof cabinets are isolated and have automatic con-

trol of temperature and relative humidity. The ideal

relative humidity should be the result of the addition

of dough hydration and moisture from the flour (for

example, if water added to the mixture is 55%, and

the flour moisture is 14%, the ideal relative humidity

will be 69%), so the dough will be neither rough nor

sticky.

Types of Proof Cabinet

0040There are several different types of proof cabinet: the

traditional fermentation cabinet, the controlled

fermentation cabinet, and the block fermentation

cabinet.

0041Traditional fermentation cabinet In this cabinet,

only heat and humidity are used. The usual condi-

tions are: temperature of 28–32



C and relative

humidity of 70–85%. If a high temperature

(> 30



C) is used, a high relative humidity (> 75%) is

also required.

0042When the temperature is > 28



C, during dough

fermentation, lactic and butyric acid are formed,

increasing in numbers with increasing temperature.

Also, the enzymatic reactions in dough are more

active at these temperatures, so the dough is softer,

the bread volume increases considerably, and the

bread is insipid and has a shorter shelf-life.

0043If the temperature is < 26



C, there is less produc-

tion of lactic and butyric acid during the fermenta-

tion, the fermentation time is longer, the enzymes are

less active, and the bread volume is lower, but the

bread has a good flavor.

0044The reduction in the amount of yeast and the

increase in fermentation time lead to a bread with a

firm crumb and thick crust.

0045Controlled fermentation cabinet This cabinet con-

trols dough fermentation temperature allowing

progressive heating. Previously, these cabinets did

not canalize the air, and the dough was rough.

Heating was rapid, and there was condensation on

the dough surface, which gave a red and translucent

crust. The result was bread with great variations in

quality, color and volume. Nowadays, these cabinets

have a regulating system, depending on the size and

volume of the pieces, but there are four phases: block,

refrigeration, heating, and fermentation.

0046Block In the first phase, the dough is cooled, and

fermentation is stopped when the temperature in the

dough reaches about 2



C. Usually, temperatures of

about 2



C(0to14



C) are used.

0047Refrigeration In this phase, the temperature of

the dough is usually at 0–2



C until fermentation

begins.

0048Heating In this phase, there is a gradual increase in

temperature to prevent the dough surface becoming

rough. The dough temperature increases gradually

until the fermentation temperature is reached.

652 BREAD/Dough Fermentation

0049 Fermentation It is very important to regulate the

temperature and relative humidity to ensure uniform

fermentation of dough.

0050 Block fermentation cabinet This cabinet has only

two phases: block and refrigeration. The functions of

these phases are the same as that of the controlled

fermentation cabinet, but the dough temperature

needs to be increased before fermentation. The dough

is kept in this cabinet for some time before fermenta-

tion, and another cabinet is needed for fermentation.

Physical and Chemical Changes in Dough

During Fermentation

0051 The transformation of the dough into bread is very

complex, because dough contains very reactive chem-

ical compounds, enzymes, microbial flora, different

ingredients, and additives (depending on the formu-

lation). In addition, the formation of dough may have

different processing conditions (depending on the

breadmaking systems used). Therefore, bread shows

great variations in organoleptic characteristics. Most

of the chemical, biochemical, and microbiological

modifications that take place, during fermentation

depending on processing conditions, thus it may be

possible to lead fermentation in some way by control-

ling the conditions.

0052 Yeast’s functions during fermentation are:

0053 to produce enough CO

and in time increase the

dough and make the dough softer;

0054 to modify the physical properties of gluten, for the

maturation of the dough;

0055 to decrease the pH of the dough, thus allowing

lactic bacteria to grow;

0056 to produce certain chemical compounds that give

bread its characteristic flavor; and

0057 to modify the bread volume and texture.

The functions of lactic acid bacteria during fermenta-

tion are:

0058 to produce acids that inhibit the development of

undesirable microorganisms, producing the condi-

tions for enzymatic processes.

0059 to produce catabolites that influence the dough

rheology and the sensorial characteristics of bread.

0060 During fermentation, the dough undergoes several

changes, such as weight loss and changes in carbo-

hydrates, phytates, lipids, nitrogen compounds, and

flavor and aroma compounds.

Weight Loss

0061 The decrease in dry matter content (fermentation

loss) during fermentation observing can be estimated

by the volume of carbon dioxide evolved. The major

proportion of carbon dioxide produced during

fermentation results from alcoholic fermentation,

and other fermentations may contribute about 5%.

During alcoholic fermentation, the consumption of

1 mol of glucose produces 2 mol of carbon dioxide,

according to Gay Lussac’s law, and 1 ml of carbon

dioxide released corresponds to a decrease in dry

matter content of 3.65 mg. Thus, fermentation loss

is influenced by the breadmaking processes used, and

the straight dough method has less fermentation loss

than the sponge and dough process (3.2% versus

5.5%, based on flour weight). In the Chorleywood

process, the yield of bread from flour is about 4%

higher than in bread made by traditional methods.

This difference is due to a substantial decrease in

fermentation losses.

Changes in Carbohydrates, Phytates, and Lipids

0062The carbohydrate concentration decreases during

fermentation. The most important change during

the fermentation is the transformation of fermentable

sugar into carbon dioxide and ethanol by yeast action.

0063Sugar metabolism by yeast has already been

mentioned. Sugar metabolism may be changed by

temperature conditions (fermentation being con-

trolled). Increasing the sugar concentration increases

gas production up to the limit of osmotic pressure at

which yeast cannot survive. Decreasing the pH in-

creases gas production.

0064Another path for sugar metabolism is by lactic acid

bacteria. Heterofermentative lactic acid bacteria pro-

duce carbon dioxide, but this gas production is less

than that from yeast (Figure 4). The principal func-

tion of lactic acid bacteria is to decrease the pH, and

increase the aroma and flavor of bread.

0065The lactic acid/acetic acid relationship is very im-

portant, because it influences the aroma and flavor of

bread. For rye bread, this relationship is closer than

that of wheat bread, and the intensity of bread flavor

is higher. The production of acids may be controlled

Homofermentative lactic acid bacteria (Pathway EMP)

Heterofermentative lactic acid bacteria (Pathway HMP)

Heterofermentative facultative lactic acid bacteria

Glucose

Lactic acid

Lactic acid + Acetic acid + Ethanol + CO

Lactic acid (Pathway EMP)

Lactic acid + Acetic acid + Ethanol

Hexose (Glucose)

Pentose (Ribose, Arabinose)

fig0004Figure 4 Metabolism of sugar by homofermentative and

heterofermentative lactic acid bacteria.

BREAD/Dough Fermentation 653

by adding acid-producing microorganisms, such as

heterofermentative facultative lactic acid bacteria,

which produce acetic acid. The hydration of dough,

temperature, and presence of yeast also have an

influence on production of acids.

0066 In terms of chemical changes in starch, as men-

tioned earlier, starch is a source of sugar for fermen-

tation. a-Amylases hydrolyze damaged starch

forming the substract for b-amylases action yielding

the breakdown products dextrin and maltose.

0067 In terms of nondigestible carbohydrates, the con-

centration of fiber increases during fermentation, and

in long periods of fermentation, there is an increase in

the amount of hemicelluloses.

0068 Phytates are associated with the fiber content. Phy-

tic acid in wheat and flour is present as phytine asso-

ciated with calcium and magnesium. Phytine has a

heterogeneous distribution in the kernel of wheat.

There is a greater proportion of phytine in the germ

and bran than in the endosperm. During fermenta-

tion, there is dephosphorylation of phytic acid by

phytase, and the concentration of phytate decreases,

decreasing the capacity to form a complex with

minerals and protein.

0069 Concerning lipids, polar lipids improve the struc-

ture of bread and increase the soft crumb. Nonpolar

lipids deteriorate the structure of bread and decrease

the bread volume.

Changes in Nitrogenous Compounds

0070 The effects of fermentation on nitrogenous com-

pounds are as follows: (1) there is a modification

in the structure of gluten, thus making the dough

more extensible and improving the gas retention;

(2) there are changes in amino acids, peptides, and

other soluble compounds, which are precursors of

the flavor and aroma of bread, and a source of

nutrients.

0071 The protein network in dough is able to retain

carbon dioxide in the air bubbles and is sufficiently

elastic to expand without disrupting during the fer-

mentation and when the gas volume increases during

baking. This is possible because of the chemical

changes in the bonds of gluten and other wheat pro-

teins. The mechanical work during the dough mixing

process breaks some of the hydrogen and disulfide

bonds, linking adjacent protein chains, and the new

bonds formed are in different positions. Expansion of

the gas formed during fermentation produces new

bond changes, thus improving the dough extensibility.

When the dough matures, there is a balance between

the consistency of the three-dimensional protein net-

work, its extensibility, and its permeability.

0072 Amino acids and peptides may be formed by

proteolysis of the dough. Lactic acid bacteria have

proteinases and peptidases, and the free amino acids

and peptides may be metabolized by the yeast. During

fermentation, the amino acids may lose an atom of

carbon giving an aldehyde or two or more atoms

of carbon, yielding inferior organic acids or hydro-

carbons. The breakdown products of oxidation and

reduction of aldehyde yield acid and alcohol, respect-

ively. Alcohols and acids react to yield esters, and

thus, there are a many compounds related to aroma

and flavor (Figure 2).

0073The amino acids are precursors of aroma and

flavor from the Maillard reaction, which takes place

during baking. The overfermentation of dough de-

pletes the amino acids and the color and flavor of

bread decreases.

0074In conclusion, depending on the breadmaking pro-

cess used, and if sourdough is added, the organoleptic

characteristics of bread will be different, due to their

influence on changes that take place in dough during

fermentation.

See also: Bread: Dough Mixing and Testing Operations;

Breadmaking Processes; Sourdough Bread;

Carbohydrates: Metabolism of Sugars; Dietary Fiber:

Effects of Fiber on Absorption; Flour: Analysis of Wheat

Flours; Phytic Acid: Nutritional Impact; Protein:

Requirements; Functional Properties; Quality; Starch:

Structure, Properties, and Determination; Functional

Properties; Wheat: Grain Structure of Wheat and Wheat-

based Products; Yeasts