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

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plants. Though an orange cauliflower is now being

marketed, the application of this research may result

ultimately in the introduction of higher-carotenoid

varieties of some of the world’s staple crops and a

reduced incidence of vitamin A deficiency (which

can be reduced by ingestion of b-carotene-rich foods).

0078 The brassica vegetables, though not unique in this

respect, are also good sources of various flavonoids

and their conjugates to which significant antioxidant

activity has been ascribed. For example, the preven-

tion of lipid peroxidation for which these compounds

appear to be reasonably well suited may be an

important mechanism for reducing the severity of

age-related degenerative diseases such as arthritis,

cardiovascular disease, and cancer.

See also: Antioxidants: Natural Antioxidants; Synthetic

Antioxidants; Synthetic Antioxidants, Characterization

and Analysis; Role of Antioxidant Nutrients in Defense

Systems; Cancer: Diet in Cancer Prevention; Functional

Foods; Glucosinolates; Goitrogens and Antithyroid

Compounds; Salad Crops: Dietary Importance; Leaf-

types; Vegetables of Temperate Climates: Cabbage and

Related Vegetables; Oriental Brassicas; Vegetarian

Diets; Vitamin K: Properties and Determination;

Physiology

Further Reading

Facciola S (1990) Cornucopia: A Source Book of Edible

Plants. Vista, CA: Kampong.

Fahey JW and Stephenson KK (1999) Cancer chemoprotec-

tive effects of cruciferous vegetables. HortScience 34(7):

1159–1163.

Fahey JW, Zhang Y and Talalay P (1997) Broccoli sprouts:

an exceptionally rich source of inducers of enzymes that

protect against chemical carcinogens. Proceedings of the

National Academy of Sciences of the United States of

America 94: 10367–10372.

mez-Campo C (ed.) (1999) Biology of Brassica Coeno-

species. Amsterdam: Elsevier.

Gray AR (1982) Taxonomy and evolution of broccoli.

Economic Botany 36: 397–410.

Kays SJ and Dias JCS (1996) Cultivated Vegetables of the

World. Athens, GA: Exon Press.

Lucier G (1999) Broccoli: Super food for all seasons.

Agricultural Outlook April: 8–12. Washington, DC:

Economic Research Service, USDA.

Rupp R (1987) Blue Corn and Square Tomatoes.

Pownal, UT Storey Communications/Garden Way

Publishing.

Seelig RA (1971) Fruit & Vegetable Facts and Pointers.

Alexandria, UA: United Fresh Fruit and Vegetable Asso-

ciation.

Switzer S (1727) The Practical Kitchen Gardiner. London:

Thomas Woodward.

Toussaint-Samat M (1987) A History of Food (trans.,

1992). Cambridge, MA: Blackwell.

Tsunoda S, Hinata K and Gomez-Campo C (1980) Brassica

Crops and Wild Allies: Biology and Breeding. Tokyo:

Japan Scientific Societies Press.

Vaughan JG, MacLeod AJ and Jones BMG (eds.) (1976)

The Biology and Chemistry of the Cruciferae. London:

Academic Press.

Zhang Y, Talalay P, Cho C-G and Posner GH (1992) A

major inducer of articarcinogenic protective enzymes

from broccoli: Isolation and elucidation of structure.

Proceedings of the National Academy of Sciences of

the United States of America 89: 2399–2403.

BRAZIL NUTS

G T Prance, University of Reading, Reading, UK

Background

0001 Brazil nuts are produced in the crown of one of the

tallest trees of the Amazonian rainforest. An import-

ant dietary item of the indigenous Indian and local

populations, the Brazil nut later entered into com-

merce and is a major export of the Amazonian coun-

tries, Bolivia, Brazil, and Peru. The nuts (Figure 1) are

harvested almost exclusively from wild trees in the

forest, rather than from plantations. They are high

in protein and oils and are also a useful source of

thiamin (vitamin B

). (See Thiamin: Properties and

Determination.)

Description and Taxonomy

0002The Brazil nut comes from the species Bertholletia

excelsa Humb. & Bonpl., the only species in this

genus of the Brazil nut family, Lecythidaceae. Several

other species of the family have edible seeds, the best

known being the sapucaia nut or monkey pot

(Lecythis pisonis Cambess.). However, the sapucaia

fruits open at maturity on the trees, and the seeds are

removed by bats, rendering large-scale harvesting

almost impossible. The Brazil nuts are produced in

large, woody, round fruits that are slightly larger than

BRAZIL NUTS 615

a baseball. These fruits, or pyxidia as they are termed,

drop to the ground intact when they are mature,

14 months after flowering has taken place. Between

10 and 25 seeds, or nuts, as they are incorrectly called

according to the botanical definition of a nut, are

arranged rather like the segments of an orange inside

the pyxidium. This explains their characteristic flat-

tened triangular shape. In nature, a large terrestrial

rodent, the agouti (Dasyprocta), or squirrels open the

pyxidium and bury the nuts in caches some distance

from the parent tree; this is the means of seed disper-

sal for this species. Brazil nut gatherers go to the trees

in January to March, when the fruits are falling and

before the rodents have removed all the nuts. The

fruits are generally gathered in the morning, because

there is less danger of injury from fruit fall. The fruits

weigh 0.5–2.5 kg and fall from a height of 40–50 m,

and injury and deaths have been reported of collect-

ors struck by falling fruits. The gatherers open the

pyxidia skillfully with machetes (see Figure 2)and

pour out the nuts into their baskets. They trade their

harvest for goods, and the nuts are shipped to factor-

ies for processing. Before exportation, they are pas-

teurized with steam to kill toxic fungi, and in many

cases, they are also shelled and canned.

Distribution and Ecology

0003Brazil nuts grow in nonflooded rainforests of the

Guianas and Amazonian Colombia, Venezuela, Peru,

Bolivia, and Brazil. They tend to grow in natural

clusters or stands of 50–100 trees. These stands are

known as manchales in Peru and castanhais in Brazil.

Usually, there are one or less trees per hectare, but

stands of 15–20 trees per hectare have been reported

in Madre de Dios, Peru. Some of the clustering may

be the result of planting by Indians who formerly

occupied the area. Brazil nuts grow in forests with

an annual rainfall of 1400–2800 mm and do better

where there is at least a short, dry season. The trees

are light-demanding, i.e., they need gaps in the forest

before they can grow to adult size.

Flowering and Pollination

0004Flowering occurs in the dry season, which begins in

September and can extend until February. The peak

of flowering is September and October throughout

most of central and eastern Amazonia, and slightly

earlier to the west. After flowering and pollination,

the fruits take approximately 14 months to mature

and fall off in January and February.

fig0002Figure 2 Brazil nut gatherer opening nuts. Reproduced from

Brazil Nuts, Encyclopaedia of Food Science, Food Technology and

Nutrition, Macrae R, Robinson RK and Sadler MJ (eds.), 1993,

Academic Press.

fig0001 Figure 1 Brazil nuts. Reproduced from Brazil Nuts, Encyclo-

paedia of Food Science, Food Technology and Nutrition, Macrae R,

Robinson RK and Sadler MJ (eds.), 1993, Academic Press.

616 BRAZIL NUTS

0005 The flowers have a complicated androecium struc-

ture, which forms a closed hood over the top of the

flower. Nectar is produced inside the hood. Large

bees are the only insects that have the strength to

force open the flower to reach the nectar. As the

bees force open the springed hood, their backs are

forced against the pollen-bearing stamens and the

stigmatic surface where pollen is deposited. The bees

therefore carry the pollen from flower to flower. Bees

that have been found visiting Brazil nut flowers are

from the genera Bombus, Centris, Epicharis, and

Eulaema. The Brazil nut is largely self-incompatible,

i.e., the tree requires pollen from another tree in order

for seed set to take place. Low seed set has been found

in trees that are isolated in forest clearings and in

areas of disturbance. The maintenance of the pollin-

ation system is essential for the production of Brazil

nuts. Therefore, plantations that are surrounded by

forest where the pollinators thrive are much more

likely to be productive than plantations that cover

larger open areas away from the forest.

Chemistry

0006 The Brazil nut is rich in oil and protein (see Table 1).

The oil extracted from the seed is bright yellow,

almost odorless, and with a pleasant nutty taste. It

has a specific gravity of 0.9165 at 15



C, solidifies at

4



C and does not become rancid easily. The first

extraction of oil from the seeds yields an excellent

cooking oil, and the second extraction produces an oil

suitable for making soap and burning in lamps.

Hence, it furnished many of the needs of the Indian

population of Amazonia. The residue left after

pressing the seeds can be used as an animal feed.

The average protein content of defatted Brazil nut

flour is about 46% and contains all the essential

amino acids, making both the nut and the flour highly

nutritious. The principal amino acid content of the

nuts is given in Table 2, which shows them to be rich

in leucine. The nuts also contain vitamin A, vitamin

(thiamin), vitamin B

(riboflavin), and niacin,

being a particularly good source of thiamin and

niacin.

0007Brazil nuts contain selenium, a powerful anti-

oxidant. The amount in a Brazil nut (16–30 mgg

1

)

exceeds the US recommended daily dose. Some

people consume a Brazil nut a day to achieve the

recommended dose. Brazil nuts can cause hair loss if

consumed in large quantities owing to their selenium

content. Brazil nuts accumulate selenium because of

the similarity of this element to sulfur. There is often a

sulfur deficiency in Amazonian soil, especially after

long-term harvesting of the nuts. If the soil is selen-

ium-rich, this is used by the plant as a substitute for

sulfur. When sulfur fertilization is used, the selenium

content of the nuts is reduced. Brazil nuts are rich in

the sulfur amino acids methionine and cysteine. (See

Amino Acids: Properties and Occurrence; Niacin:

Properties and Determination; Retinol: Properties

and Determination; Riboflavin: Properties and Deter-

mination; Thiamin: Physiology.)

tbl0001 Table 1 Chemical properties of Brazil nuts (as a percentage of the total weight)

Seeds from Peru

Seeds from Brazil

SeedsfromBrazil

Seeds fromBrazil

Oil 65.0 67.0 70.0 67.45

Protein 17.0 17.0 13.9 15.48

Ash 3.0 4.0 3.89

Crude fiber 0.9 3.21

Water 4.0 5.0 2.0 5.49

Carbohydrates 10.1 7.0 3.83

Ash/fiber/carbohydrates 14.1

100.0 100.0 100.0 99.80

From Sa

nchez JS (1973) Explotacio

n y comercializacio

n de la Castan

a en Madre de Dios. In: Informe No. 30. Lima: Ministerio de Agricultura, Direccio

General de Forestall y Caza.

From SUDAM (Superintende

ncia do Desenvolvimento da Amazonia) (1976) Estudos e pesquisas sobre a castanha-do-Par˜. Bele

m, Brazil: Ministerio do

Interior, Departamento de Recursos, Naturais.

From Knuth (1939) Lecythidaceae. In: Engler A (ed.) Pflanzenreich IV, vol. 219a, pp. 1–146.

tbl0002Table 2 Principal amino acids found in the Brazil nut

Amino acid content

(mgper kilogram fresh weight)

Lysine 4313

Threonine 3263

Valine 4888

Methionine 4088

Leucine 9250

Isoleucine 3450

Phenylalanine 4385

Tryptophan 1400

From SUDAM (Superintende

ncia do Desenvolvimento da Amazonia)

(1976) Estudos e pesquisas sobre a castanha-do-Par˜. Bele

m, Brazil:

Ministerio do Interior, Departamento de Recursos, Naturais.

BRAZIL NUTS 617

Economic Botany

0008 Until recently, Brazil nut seeds were second only

to rubber as an export crop from Amazonian Brazil.

The production from 1933 to 1986 has ranged from

a low of 3557 tonnes in 1944 to 104 487 tonnes

in 1970 (Figure 3). The production in 1986 was

36 136 tonnes. The low of 1944 was caused by

World War II. In the Department of Madre de Dios

in Peru, 20% of the forests are rich in Brazil nuts, and

it is estimated that two-thirds of the population are

engaged in Brazil nut extraction and processing. The

annual production of nuts from the state of Pando in

Bolivia is estimated to be between 10 and 12 000

tonnes. Most of the seeds are exported to France,

the UK, the USA, and Germany. Very little on the

crop is consumed domestically in either Brazil or

Peru. Recent price fluctuations of Brazil nuts on the

commodity market have made it harder for the pro-

ducers. The nuts are exported intact or with the seed

coat removed. In the latter case, the seeds are soaked

for 8–10 h in a tank of water, after which they are

submerged in boiling water for 1–2 min. The seeds are

dried to make the embryo shrink away from the seed

coat; this facilitates the removal of the seed without

breakage. Broken seeds have a lower export value and

are often used locally for oil extraction and in the

soap industry. The dried seeds are placed in a manual

press, and pressure is applied at both ends to crack

open the seed coat (see Figure 4). The seeds are

canned for export. Brazil nuts can be eaten raw or

roasted, and are used in confectionery.

0009 Brazil nut oil is often used in soaps, shampoo, and

hair and skin conditioning products. It is a good

moisturizer for the skin and provides antioxidant

benefits. Brazil nuts require careful handling and

steam sterilization, because they are highly suscep-

tible to bruising and molding, which can cause

the accumulation of aflatoxins. Sometimes, whole

batches of nuts exported in their shells have to be

rejected because of the danger of aflatoxins. This is

rare in properly prepared and packaged nuts.

0010In addition to producing the nut, Brazil nut trees

yield excellent timber. Although it is against the law

to fell Brazil nut trees in Brazil, there is still a clandes-

tine market for its timber. The timber is also used in

Peru. The fibrous bark of the tree is used for caulking

boats, and in folk medicine, a bark tea is used as a

cure for liver ailments. The empty fruit cases are used

for fuel and for making a vast array of tourist

souvenirs. The world-wide Brazil nut market in 1999

was estimated to be $35 million.

See also: Amino Acids: Properties and Occurrence;

Niacin: Properties and Determination; Retinol:

Properties and Determination; Riboflavin: Properties and

Determination; Thiamin: Properties and Determination;

Physiology

Further Reading

Chang JC et al. (1995) Selenium content of Brazil nuts from

two geographic locations in Brazil. Chemosphere.

110

100

1935 1940 1945 1950 1955 1960 1965 1970 19801975 1985

⫻ 10

fig0003 Figure 3 Brazil nut seed production from 1933 to 1984 (data from the Anu

rio Estat

stica do Brasil). Reproduced from Brazil Nuts,

Encyclopaedia of Food Science, Food Technology and Nutrition, Macrae R, Robinson RK and Sadler MJ (eds.), 1993, Academic Press.

fig0004Figure 4 Cracking Brazil nuts in a processing factory, O

bidos,

Brazil. Reproduced from Brazil Nuts, Encyclopaedia of Food Sci-

ence, Food Technology and Nutrition, Macrae R, Robinson RK and

Sadler MJ (eds), 1993, Academic Press.

618 BRAZIL NUTS

Knuth R (1939) Lecythidaceae. In: Engler A (ed.) Pflanzen-

reich IV 219a: 1–146.

Mori SA and Prance GT (1990a) Taxonomy, ecology, and

economic botany of the Brazil nut (Bertholletia excelsa

Humb & Bonpl.: Lecythidaceae). Advances in Economic

Botany 8: 130–150.

Mori SA and Prance GT (1990b) Lecythidaceae – Part II.

Flora Neotropica Monograph 21: 1–375.

Moritz A (1984) Estudos biolo

gicos da castanha-do-Brasil

(Bertholletia excelsa H.B.K.). EMBRAPA, Centro de

Pesquisa Agropecua

rio do Tro

pico Umido Documentos

29: 1–82.

ller CH (1981) Castanha-do-Brasil; estudos agrono

mi-

cos. EMBRAPA, Centro de Pesquisa Agropecua

rio do

Tro

pico Umido. Miscela

nea 2: 1–25.

Nelson BW, Absy ML, Barbosa EM and Prance GT (1985)

Observations on flower visitors to Bertholletia excelsa

H.B.K. and Couratari tenuicarpa A.C.Sm. (Lecythida-

ceae). Acta Amazo

nica 15(supplement 2): 225–234.

nchez JS (1973) Explotacio

n y comercializacio

ndela

castan

a en Madre de Dios. In: Informe No. 30. Lima:

Ministerio de Agricultura, Direccio

n General de

Forestall y Caza.

Souza AH (1963) Castanha-do-Para

; estudo bota

nico, quı

mico e tecnolo

gico. Edic¸o

es S.I.A. Estudos Te

cnicos 23:

1–69.

SUDAM (Superintende

ncia do Desenvolvimento da Ama-

zonia) (1976) Estudos e pesquisas sobre a castanha-do-

Para

. Bele

m, Brazil: Ministerio do Interior, Departa-

mento de Recursos, Naturais.

Sun SS et al. (1987) Properties, biosynthesis and processing

of a sulfur-rich protein in Brazil nut (Bertholletia excelsa

H.B.K.). European Journal of Biochemistry 162: 477–

483.

Vaz Pereira IC and Lima Costa SL (1981) Bibliographia de

Castanha-do-Para

(Bertholletia excelsa H.B.K.). Bele

Brazil: EMBRAPA, Centro de Pesquisa Agropecua

rio do

Tro

pico Umido.

BREAD

Contents

Dough Mixing and Testing Operations

Breadmaking Processes

Chemistry of Baking

Sourdough Bread

Dietary Importance

Dough Fermentation

Dough Mixing and Testing

Operations

S D Deshpande, Central Institute of Agricultural

Engineering, Bhopal, India

Dough Mixing

0001 One of the most important operations in a bakery is

the accurate and thorough mixing of ingredients.

Mixing reduces nonuniformities of gredients in com-

position, properties, or temperature of bulk materials

or products in and out of a reactor, and was defined

by Quillen as the ‘intermingling of two or more dis-

similar portions of a material, resulting in the attain-

ment of a desired level of uniformity, either physical

or chemical, in the final product.’ The term ‘mixing’

includes more than just the mechanical actions that

blend ingredients to a homogeneous mass. There may

also be an incorporation of air and the formation of

minute bubbles in a fat/water phase, a development of

hydrated flour proteins into an elastic mass known as

gluten, and an increase of temperature by a build up

of mechanical heat. There is no fundamental basis for

classifying the gluten proteins on the basis of aqueous

alcohol extractability, although such a classification

does have technological significance. Gliadin and glu-

tenin are known to impart entirely different physical

properties to the gluten network in a wheat-flour

dough. Gliadin behaves mainly as a viscous liquid,

when hydrated, and confers extensibility, allowing

the dough to rise during fermentation, whereas glute-

nin provides elasticity and strength, preventing the

dough from being overextended and collapsing either

during fermentation or in baking. This article dis-

cusses the purpose of kneading of dough, types of

mixers for dough, dough mixing and dough develop-

ment, and empirical methods in physical dough

testing.

BREAD/Dough Mixing and Testing Operations 619

Purpose of Dough Mixing

0002 The dough is kneaded before it is allowed to ferment,

and again before it is molded into the desired shapes.

The purpose of kneading is to remove some of the

excess carbon dioxide in order to prevent over-

stretching of the gluten strands, and to distribute the

yeast cells throughout the dough. Kneading also tends

to keep the dough at a uniform temperature. The

dough is kneaded sufficiently when it has a smooth,

‘satiny’ surface, and small bubbles appear under the

surface.

Mixing of Dough – Dimensional Analysis

0003 Dough mixing is the most common unit operation in

the food industry, finding widespread application in

the bakery, snack food, and breakfast cereal indus-

tries. Dimensional analysis of this operation reveals

how potential scale-up problems can be diagnosed

before any experimentation is initiated.

0004 Consider the schematic representation of a dough

mixer that is shown in Figure 1. Cereal chemists

generally consider the specific energy input as being

indicative of the degree of ‘development’ of the

dough. Specific energy is defined as the total energy

dissipation per kilogram of dough. Assuming that the

dough is Newtonian, one can perform a dimensional

analysis for the power consumed by a dough mixer.

The key variables used are given in Table 1.

0005 By inspection, the dimensionless relationship that

is sought is

¼ f

;



: ð1Þ

0006Solving for power and making use of the general

rule that in laminar flow, the power is proportional to

the velocity squared, it can be shown that

PamN

;



: ð2Þ

0007The specific energy is simply the power dissipation

multiplied by the mixing time divided by the mass of

dough in the mixer. Then, the required time of mixing

is given by

t ¼

ð3Þ

where o ¼specific energy input. If the scaled-up

mixer is geometrically similar to the pilot mixer, this

simplifies to

: ð4Þ

0008A conclusion can be drawn from eqn (4). If

the plant mixer operates at the same speed as the

pilot plant mixer, the times required for developing

the dough are identical. This provides the designer

with a clear-cut direction as to how to design the

scaled-up mixer. Unfortunately, for most actual appli-

cations, geometric similarity is not maintained when

scaling up bakery mixers.

0009How does one handle a real dough with

non-Newtonian properties? Complete analysis is im-

possible since the dough exhibits very complicated,

time-dependent behavior. However, one can draw

some useful inferences from the non-Newtonian ana-

lyses that follow.

0010If the dough were a simple power law fluid, the

viscosity in the list of variables would be replaced by

the flow consistency and the flow index. The result of

the dimensional analysis would be

¼ f

2n

; ...; n



: ð5Þ

Rolling bar

Spider

Driven shaft

Stationary bar

fig0001 Figure 1 Schematic representation of a dough mixer. From

Valentas KJ, Leuine L and Clark JP (1991). Dimensional analysis

– mixing and sheeting of doughs. In: Food Processing Operations

and Scale-up, pp. 359–361. New York: Marcel Dekker, with permis-

sion.

tbl0001Table 1 Key variables used in the text

Variable Description Units

P Power ML / T

r Density M / L

m Viscosity M / LT

N Rotational speed 1 / T

F Volumetric charge L

d Roller diameter L

b Breaker bar diameter L

D Mixer diameter L

h Clearance between rollers and wall L

t Clearance between breaker and rollers L

L Length of mixer L

620 BREAD/Dough Mixing and Testing Operations

0011 The time required to mix the dough is then

1þn

: ð6Þ

0012 As before, if geometric similarity is maintained,

the time required to mix the dough is held con-

stant on scale-up if the speed of the mixer is held

constant.

0013 For a viscoelastic dough, which can be approxi-

mated as a Maxwell body, the variable list would

have the relaxation time added. The new dimension-

less group that appears to incorporate this new term is

the Weissenberg (Deborah) number. The result is

¼ h

; y



; ð7Þ

where y

is the relaxation time of the dough. The

conclusions are unchanged. No matter how compli-

cated a model, even a model containing an infinite

number of relaxation times, the conclusion is the

same.

Types of Mixers for Dough

0014 Mixers and kneaders are necessary for the proper

blending or mixing of the various ingredients. Liquids

can be easily blended using propeller-type agitators in

a tank. For blending of premixes or preparation of

adjuncts, ribbon blenders, twin-cone, and V-shell

blenders are usually employed when dry ingredients

are to be mixed.

0015 Dough mixing can be carried out using horizontal,

vertical, reciprocating, or continuous mixers as re-

quired. The horizontal type may have a fixed or tilting

bowl, while the vertical mixer may be a planetary or

fixed spindle type. The continuous mixers may be of

the agitator-in-tube type, or the rotor and stator head

type.

Horizontal Dough Mixers

0016 These mixers can be used to mix various mixtures

ranging in consistency from thin batters to tough

doughs. They must be used when gluten development

is desirable, e.g., in breadmaking. These mixers have

a horizontal U-shaped bowl mounted on a rigid frame

with a drive motor. Their capacities range from 10 kg

upwards. Bowls are usually made of stainless steel or

stainless steel-clad mild steel. Bowls are sometimes

provided with jackets for the circulation of cold or

hot water.

0017 High-speed mixers for gluten development usually

contain a single axle on which two or more arms

parallel to the front of the mixer are mounted. The

limited clearance between the jacket wall and the

agitator bars causes the dough to be repeatedly

stretched and kneaded, resulting in quick gluten

development. These mixers can usually be operated

in two speed ranges, namely 30–60 and 40–80 r.p.m.

In the slow-speed mixers, agitators of various forms,

e.g., eight-arm, Z, etc., are employed on one or two

axles.

0018The agitator configuration and its speed affect the

action. Slow-speed Z or eight-arm mixers have a

speed range of 14–60 r.p.m. (25 r.p.m. on an average).

0019The high-speed horizontal mixers are also called

kneaders, and may contain bars projecting from the

axle at right angles, while the bowl has radical bars

intermeshing with axle bars. This construction gives

very efficient dough kneading, and is particularly

suitable for tough doughs.

0020The dough is discharged from these mixers by

tilting the bowl so that the top is brought to a for-

ward-facing position. In some models, the front of the

bowl consists of a tightly fitting door, which can be

raised and lowered independently of the immobile

section of the bowl, and the dough is discharged

through this door. The bowl-tilting mechanism may

be hand-operated or it may be operated by a separate

motor.

Vertical Mixers

0021Vertical mixers consist of a movable bowl or trough

with one or two vertical shafts that may be stationary

or may have planetary movement. The agitators

themselves may be of various sizes and configurations.

The most important design in the vertical mixer is the

planetary mixer, which is particularly suitable for

mixing batters or adjuncts such as icings. The agitator

is called ‘planetary’ as it, apart from revolving around

its own vertical axis at a relatively high speed, also

moves in circles as it rotates around the bowl. This

motion ensures ‘beater’ action throughout the bowl

contents. The agitator may be provided with a vari-

able-speed mechanism, and the bowl can be raised

and lowered by a separate drive. The agitator may be

of any of the various types available, e.g., simple,

curved single-arm, wire meshing, or paddle gate.

0022The hook-type agitator gives a good kneading

action to the dough, resulting in development of the

gluten with a minimum of tearing. The wire-mesh

type agitator gives a good ‘beater’ action with

maximum air incorporation. The paddle-type agita-

tor ensures good mixing coupled with scraping of the

bowl sides. Bowls are usually provided with covers to

prevent splashing or dusting. Capacities range from

10 kg upwards.

0023Spindle-type mixers are used mainly for biscuit

doughs. Their special advantage is with saltine

doughs, in which case they are adapted for mixing

BREAD/Dough Mixing and Testing Operations 621

in special mobile troughs used for fermentation.

Thus, sponges and doughs need not be transferred in

and out of the mixer between the various stages. The

spindle speed is usually low, and spindles can be

raised to allow the trough to be rolled into place

under them. The mixer blades are so designed as to

give a cutting action rather than a kneading or

stretching action to the mix, thus a toughening effect

on the cracker or biscuit doughs is avoided. (See

Biscuits, Cookies, and Crackers: Methods of Manu-

facture.)

0024 In reciprocating agitator or revolving bowl

mixers, a pair of agitator arms travels through

intersecting elliptical paths in a shallow, slowly re-

volving bowl. These mixers are useful for mixing

temperature-sensitive doughs, and also where nuts

and raisins in the mix are to be kept unbroken.

Their output is usually low compared with horizontal

mixers, and they are particularly suitable for pie

doughs and puff pastry.

Dough Mixing and Dough Development

Dough Properties and Mixing Behavior

0025 It is generally agreed that the uniqueness of wheat is

due to its breadmaking quality. Among plant crops,

only wheat flour and, to a limited extent, rye flour

have the ability to form a dough that retains gases and

produces a baked product, particularly leavened

bread, with the desired eating qualities. Wheat-flour

doughs exhibit a wide range of properties when dif-

ferent flour samples are compared. Dough properties

influence both the efficiency of throughput in the

manufacturing plant and the quality of the final

baked product. In discussing the state of dough prior

to baking, we need to differentiate between the con-

tributions from the individual flour and those from the

various treatments, which include added ingredients,

mixing, and intermediate punching, and molding

steps. Dough is a complex material from a rheological

point of view. Knowledge about its structure comes

from fundamental rheological studies, from standard

physical dough testing, including mixing, and from

microscopy.

0026 Because of the trend towards greater use of baking

processes involving intensive mixing and short

fermentation times, much more attention has been

given to basic studies of dough mixing in recent

years. These studies have highlighted the sensitivity

of dough structure to the conditions to which the

dough has been subjected during its development. It

is clear that meaningful interpretations of rheological

measurements can be made only if the state of dough

development is well understood.

Factors Affecting Dough Development

0027The first step in converting flour into bread is the

mixing of flour, water, and other additives. Specific

additives have been incorporated as improvers to

wheat flour. The effects of addition of sodium algin-

ate at 0.1–0.5% levels to wheat flour have been stud-

ied, and it has been observed that sodium alginate can

improve the gas formation/retention power of dough,

thus making it suitable for producing better bread. As

mixing proceeds, the initially incoherent dough mass

develops viscoelastic properties and finally acquires a

sheen, this stage being termed ‘clearing.’ Prolonged

mixing past this point causes the dough to lose its

strength and become plastic and very sticky to the

touch. If the torque on the pins, blades, or arm of

the mixer is monitored against time, the trace rises,

reaches a maximum, and then falls steadily. This is

illustrated in Figure 2 for doughs mixed in a

mixograph. Optimum bread-baking performance

is usually achieved in a region at, or slightly past,

the peak development point.

0028Critical mixing intensity and critical work input

Two parameters are critical for optimum develop-

ment and hence best performance. These are that

fig0002Figure 2 Mixogram traces. The sequence from A through D

may be used to represent either doughs of increasing mixing

requirements mixed at a fixed intensity, one dough mixed at

increasing intensities or one dough mixed at a fixed intensity

but containing increasing additions of cysteine.

622 BREAD/Dough Mixing and Testing Operations

(1) the mixing intensity must be above a minimum

critical value, and (2) the total work imparted to the

dough must be above a certain minimum value. Both

parameters vary according to the flour used. Before

discussing these requirements more fully, it is useful

to consider the mechanical and mixing efficiencies of

different dough mixers. The distinction between these

two quantities is illustrated in Figure 3. A percentage

of the total energy consumed by the mixer motor is

available for performing mechanical work on the

dough. This is called the mechanical efficiency. How-

ever, not all of this energy is utilized for mechanical

development of the dough but that portion which is

utilized is denoted the ‘mixing efficiency’ of the mixer.

0029 Mixing requirements of flours vary widely, and

Figure 2 illustrates the mixing behavior of four flour

types. The mixing curves are for doughs that have

been mixed at a constant and moderate speed. Flour

A has high mixing requirements, and the rate of

mixing used is insufficient to develop the dough; such

a dough would be a failure in a baking test. Flour B is

a moderately strong flour that does develop at this

mixing speed, although there is an initial induction

period before the dough begins to exert any appre-

ciable torque on the mixer. Flour C is of medium

strength, and flour D is a comparatively weak flour

that develops quickly. We may also make use of

Figure 2 to illustrate the effect of varying the mixing

intensity (i.e., mixing speed) on the mixing curve of a

given dough. At a low speed, the dough does not

develop (trace A). As the mixing speed is increased,

the dough develops after a lag phase (trace B) and

thereafter develops more easily (traces C and D).

With increasing speed, and providing the amount of

work applied to the dough is above a certain level

(corresponding to a point at, or slightly past, the peak

in the trace), the baked loaf volume increases up to a

critical mixing speed, above which it plateaus.

0030For every dough, there exists a critical mixing

speed (which may vary for each mixer) below which

dough handling properties and baked loaf character-

istics are unsatisfactory. In addition, it is necessary to

have imparted a minimum level of work input to the

dough in order to bring it to an optimal developed

state. If the mixing speed or work input level is below

the critical values, unsatisfactory baking results are

obtained. Baking results are less affected by exceeding

the critical values than when these values are not

reached. However, dough-handling properties deteri-

orate, and doughs become sticky; weaker flours are

more sensitive to overmixing.

0031Activated dough development Because some flours

have very long mixing requirements or have critical

mixing speeds that exceed the capacity of many

dough mixers, methods of overcoming these limita-

tions have been devised. One method involves the

addition of reducing agents, particularly sodium

metabisulfite (SMS) and l-cysteine hydrochloride

(cysteine), to doughs. Cysteine reduces the energy

level required to achieve peak dough development,

and also the critical mixing speed necessary to pro-

duce bread of satisfactory loaf volume. We may again

make use of Figure 2 to illustrate the effect of increas-

ing additions of cysteine in altering the mixing char-

acteristics of a strong dough. As the amount of added

cysteine is increased, the nature of the mixing curve

changes from A through D. Cysteine also slightly

increases the rate of energy input at a given mixing

speed and increases the tolerance to undermixing, i.e.,

enables satisfactory bread to be produced with energy

levels less than those required to achieve peak dough

development. There is an optimum level of cysteine

addition, and too high a level causes deterioration of

loaf characteristics.

Intelligent Mixer for Bread Dough

0032To detect ‘dough development’ through digital signal

processings of the mixer’s torque and control mixing

without an ordinary mathematical model, intelligent

Total

gross energy

Mechanical

efficiency

Mixer

motor

Motor

efficiency

Linkage

gears, etc.

Net energy

Mixer

output

Mixing

efficiency

Mechanical

development

fig0003 Figure 3 Diagram illustrating the distinction between mechan-

ical and mixing efficiencies. From Kilborn RH and Tipples KH

(1972) Factors affecting mechanical dough development. I. Effect

of mixing intensity and work input. Cereal Chemistry 49: 34–47,

with permission.

BREAD/Dough Mixing and Testing Operations 623

mixer (speed variable farinograph, robots for flour–

water addition) was developed.

0033 A smoothed farinogram was obtained at constant

mixing intensity, which has a linear part and a

maximum point. Dough at the maximum point was

judged to be fully developed by experienced mixing

operators and was confirmed by the baking test. An

empirical equation about torque mixing and fuzzy

rules to correct nonlinear effects by three parameters

(water content, temperature, and mixing speed) were

obtained. Applying the equation gave a good statis-

tical relation between ‘torque increasing rate’ and

maximum torque value. This statistical relation led

to regulation of the maximum torque value (a good

indicator of dough properties) through flour (or

water) addition by robots. Addition of flour or water

in the early mixing stage caused no apparent influence

on developed dough and baked products. The wave

form of oscillating components, though there seemed

a lot of background noise, had a good correlation

with the degree of dough development. Combining

wave-form analysis with step-wise change of mixing

intensity, it was easy to find the optimum mixing

intensity at each mixing stage. Applying these results,

the intelligent mixer produced a dough with the

desired maximum torque (a good indicator of dough

properties) in a short time.

Empirical Methods in Physical Dough

Testing

0034 A great variety of commercial testing instruments are

used in routine physical tests on dough, either in

quality control or in research work. The deformation

to which dough is subjected in these instruments is so

complicated that it does not allow the evaluation of

the properties of the material in simple physical

terms. Though the results are evaluated more on an

empirical basis than through theoretical analysis, they

provide valuable information on the baking charac-

teristics of the tested material and are a useful tool.

0035 Over the years, a physical testing system has been

developed on the basis of the ‘three-phase concept of

breadbaking.’ The system has been generally accepted

and is used in many commercial milling and baking

operations. It applies three principles of testing: dough

mixing, dough stretching (load–extension), and vis-

cosity measurements on buffered flour suspensions at

elevated temperatures.

Mixing Tests

0036 The two most common instruments used for testing

wheat flour and wheat-flour dough during the mixing

operation are the Brabender farinograph and

National Recording Dough Mixer (mixograph).

0037The Brabender farinograph is essentially a torque-

measuring dough mixer that measures the plasticity

and mobility of dough upon a relatively gentle mixing

at constant temperature. The resistance of the dough

to Z-shaped mixing blades is transmitted to a dyna-

mometer connected to a mechanical recording system,

which records a curve (farinogram) on a kymograph

chart. Farinograms provide information on optimum

mixing time and dough stability on prolonged mixing

(Figure 4). Doughs are tested at a standard water

content known as the ‘farinograph water absorption’

value. This value has to be determined by ‘titration’ of

flour with water, and is the amount of water needed

for a standard optimum consistency of the dough of

500 Brabender units. ‘Forinograph water absorp-

tion,’ dough development time, and dough stability

are useful parameters for the evaluation of the

strength of a flour. In general, the higher the value

of these parameters, the stronger the flour. To express

the strength of a flour on the basis of farinograph data

as a single score, the ‘valorimetric value’ may be

determined by the dough development time and the

decreasing slope of the curve (degree of softening) –

the higher the value, the stronger the flour.

0038The National Recording Dough Mixer is another

widely used instrument for flour testing. Like the

farinograph method, the mixograph method has

become a standard physical dough test. The resist-

ance offered by the dough to four vertical pins revolv-

ing around three stationary pins in a mixing bowl

creates a force that deviates the mixing bowl from

its original position. The torque is proportional to the

shear strength and elasticity of the dough, and may be

used as an index of the dough strength. Both Braben-

der farinographs and National Recording Dough

Mixers may be modified by replacing the mechanical

recording device by an electronic strain-gauge system.

Electronic strain-gauge recording offers several

advantages: ease of calibration in terms of physical

units, greater accuracy because of the elimination of

friction from the torque measuring system, a wide

range of sensitivity, and a record on rectangular

coordinates.

0039For testing the mixing characteristics of dough

under conditions more closely related to those during

mechanical development, a variant of the farino-

graph, known as the Brabender Do-Corder, was de-

veloped. This has a nearly closed mixing bowl with

heavier mixing blades. The dough can be mixed at

higher rates than in the standard farinograph. A more

recent development is the Brabender resistograph.

The instrument was developed to meet the needs of

modern bread-baking technology in which high-

speed mixers subject the dough to both kneading

and stretching. The characteristics of doughs mixed

624 BREAD/Dough Mixing and Testing Operations