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Social Subjects 32. London: Her Majesty’s Stationery

Office (HMSO).

Department of Health (1991) Dietary Reference Values for

Food Energy and Nutrients for the UK. Report on

Health and Social Subjects 41. London: Her Majesty’s

Stationery Office.

Department of Health (1994) Weaning and the Weaning

Diet. Report on Health and Social Subjects 45. London:

Stationery Office.

Gill HS, Rutherford KJ and Cross ML (2000) Bovine milk:

a unique source of immunomodulatory ingredients for

functional foods. In: Buttriss J and Saltmarsh M (eds)

Functional Foods II: Claims and Evidence. Proceedings

of a conference held in 1998, organised by the British

Nutrition Foundation and the Royal Society of

Chemistry, pp. 82–90. Saltmarsh. Cambridge: RSC.

Holland B, Unwin ID and Buss DH (1989) Milk Products

and Eggs. McCance and Widdowson’s The Composition

of Foods, suppl. 4, 4th edn, London: Royal Society of

Chemistry and Ministry of Agriculture, Fisheries and

Food.

Kritchevsky D (2000) Conjugated linoleic acid. BNF

Nutrition Bulletin 25(4): 25–28.

McBean L (1999) Lactose intolerance. BNF Nutrition

Bulletin 24: 32–38.

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Household Food Consumption and Expenditure 1998.

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National Dairy Council (1988) From Farm to Doorstep.

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Nutrition. Munich: Volkswirtschaftlicher Verlag.

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Milk Allergy See Food Intolerance: Types; Food Allergies; Milk Allergy; Lactose Intolerance; Elimination

Diets

Milk Powders See Powdered Milk: Milk Powders in the Marketplace; Characteristics of Milk Powders

MILLETS

M I Gomez and S C Gupta, SDCC/ICRISAT,

Bulawayo, Zimbabwe

This article is reproduced from Encyclopaedia of Food Science,

Background

0001 Millets comprise a number of small-grained, annual

cereal grasses, which include several distinct botan-

ical species. The most important types are pearl,

finger, proso, and foxtail millets; other types of local

significance include kodo, little, barnyard, and

fonio millets, and teff. They differ in climatic and

soil requirements, length of growing period, grain

consistency, size, and taste. This article describes

their common names, origin, geographical distribu-

tion, plant description, and crop utilization. The

proximate composition of millets is summarized

in Table 1.(See Cereals: Contribution to the Diet;

Cereals: Dietary Importance.)

Pearl Millet

0002Pearl millet (Pennisetum glaucum (L.) R. Br.) is also

known as bulrush, cattail, or spiked millet in English,

bajra in Hindi, dukhn in Arabic, and mil a

chandelles

or petit mil in French, and as mhunga or mahango in

parts of southern Africa.

0003Most botanists consider pearl millet to have origin-

ated in Africa and to have been subsequently intro-

duced into India. Pearl millet originated in western

Africa, where the grain developed by natural selection

and acquired considerable resistance to a large

number of diseases and insects.

3974 MILLETS

0004 Pearl millet is the most widely cultivated of all

millets and is one of the most drought-tolerant of

all domesticated cereals. Soon after its domestication,

it became widely distributed across the semiarid

tropics of Africa and Asia. It is planted on some

15 10

ha in Africa and 12 10

ha in Asia. In Africa,

major pearl millet-growing countries are Nigeria

(3 133 000 t), Niger (1 227 000 t), Mali (695 000 t),

Senegal (539 000 t), Burkina Faso (447 000 t),

Sudan (355 000 t), Chad (161 000 t), and Tanzania

(144 000 t). It is also grown in Cameroon, Ghana,

Zimbabwe, Togo, Angola, Namibia, The Gambia,

Ivory Coast, Zaire, Sierra Leone, Guinea Bissau,

Kenya,CentralAfricanRepublic,andGuineawherethe

production is above 10 000 t but less than 100 000 t per

year. There are many other African countries, such as

South Africa, Benin, Zambia, Ethiopia, Mozambique,

Malawi, Libya, Mauritania, Morocco, and Botswana,

whereitisgrownonsmallacreages.InAsia,itisthemost

importantcropinIndia(5 625 000 t),followed byPaki-

stan(252 000 t)andYemen(108 000 t).Itisalsogrownin

Syria, Myanmar, and Saudi Arabia. The average grain

yield production is about 0.5 t ha

1

, but the improved

varieties with good management under dry land

conditionscanproduceupto3 tha

1

0005 Pearl millet is a robust annual grass, usually 1.2–

3.5 m tall. It is a staple cereal in India, and in some

countries of west and southern Africa, such as Senegal

and Namibia. The stems are 1–3 cm or more in diam-

eter. The plant can tiller from few to as many as

20 culms based on spacing, management, and the

cultivar. The tillering could be basal as well as

nodal. Most of the cultivars have basal tillering.

The internode is usually light green but sometimes

purple. The nodes are often marked by a ring of

long, white cilia pointing upward and bearing a

ring of adventitious roots on the basal side. The leaves

are long, scabrous, and rather slender; they may

be smooth or have hairy surfaces, and they have

hairy ligules. The blades are lanceolate, cordate, and

sometimes 90–100 cm or more in length and 5–8cm

in width. The midrib color is white or green but

sometimes brown. Leaves are upright or drooping,

and the ligule is narrowly membranous with a fringe

of hairs. The leaf sheaths are open and hairy, and the

ligule is short, Leaves and culms may vary in color

from light yellowish green to dark green and, some-

times, deep purple.

0006The ear head can be compact, semicompact or

loose, cylindrical, conical, or spindle-shaped, 2–5cm

in thickness, and usually 15–45 cm long, although

some Nigerian varieties can have ear head lengths

over 100 cm. The rachis is straight, cylindrical, solid,

often 8–9 mm thick, and unbranched. It extends the

entire length of the inflorescence, tapering gradually

from base to apex. The seeds are mostly gray but are

sometimes grayish brown, grayish white, purple,

yellowish brown, or white. Endosperm colors range

from white to yellow and gray. The individual seed

weight varies from 3 to 14 mg. The spikelets can be

without bristles or with long bristles.

0007The aleurone layer is only one cell thick, and the

endosperm consists of an outer hard or vitreous por-

tion and an inner opaque region of soft endosperm.

The hard endosperm consists of a tightly packed cel-

lular structure containing no air spaces, whereas the

soft endosperm is rather loosely packed and contains

relatively large air spaces. The soft endosperm

appears to contain no protein bodies, whereas large

protein bodies constitute the protein matrix of the

hard endosperm in which the starch is embedded.

Proximate analysis of whole pearl millet grain

shows it to have a relatively low protein content of

about 10% but a high fat content of 3.8–4%, largely

concentrated in the germ.

Processing and Food Uses

0008Pearl millets are used largely to prepare traditional,

thick or thin, fermented or unfermented porridges in

Africa. The second major use in Africa is malting for

tbl0001 Table 1 Proximate composition (% dwb) of millets

Millets

Protein (N 6.25) Lipid Fiber Ash Carbohydrate

Mean Range Mean Range Mean Range Mean Range Mean Range

Pearl (621) 11.6 8.6–17.4 4.8 1.5–6.8 2.3 1.4–7.3 2.2 1.6–3.6 75.6 61.5–89.1

Finger (227) 8.7 6.0–10.9 1.8 1.0–4.6 3.4 3.0–7.5 2.8 2.3–3.9 82.3 73.5–87.5

Common (15) 13.5 10.9–18.6 3.7 2.3–4.9 5.5 0.7–9.0 3.3 2.8–3.7 68.9 60.6–80.1

Foxtail (14) 11.8 10–15.8 4.1 2.5–6.8 7.1 6.3–8.1 3.3 1.4–5.7 66.9 63.0–72.4

Little (9) 10.7 7.5–13.8 6.0 5.3–6.8 7.0 3.7–7.6 5.9 4.6–10.1 66.3 62.6–71.0

Japanese barnyard (3) 11.3 10.2–11.6 4.0 3.0–5.1 13.9 4.6 55.7

Kodo (7) 10.2 6.6–12.1 3.9 1.5–6.6 8.4 6.2–10.5 3.6 2.9–4.1 73.5 72.5–74.0

Fonio (8) 8.7 5.1–10.4 3.5 2.1–5.2 8.5 4.6–11.3 3.8 1.8–6.0 73.6 62.7–80.0

Figures in parentheses denote the number of samples.

dwb, dry-weight basis.

Data derived from several sources and different regions.

MILLETS 3975

the brewing of traditional beers and wines. In west

African countries, e.g., Senegal, millet is used for

making couscous, pap, and fritters. In Cameroon,

pearl millet-based gruels and steamed cakes are pre-

pared for feeding infants and preschool children.

Malted pearl millet in combination with legumes

has been used to prepare malted weaning foods.

Pearl millet has also been used in composite flour

with wheat for making bread. Up to 30% pearl millet

was used successfully in making bread in Senegal. The

nutritional advantages of pearl millet are its high fat

content and a relatively high lysine content, compar-

able with that of high-lysine corn in some varieties.

Antinutritional factors, however, have been reported

in several studies. A thionamide-like substance has

been identified that interferes with the formation of

thyroid hormones, which in turn leads to undesirable

goitrogenic effects. (See Fermented Foods: Beverages

from Sorghum and Millet; Goitrogens and Antithyr-

oid Compounds.)

0009 Pearl millet is traditionally milled by hand-

pounding in a wooden mortar, yielding a flour of

about 85% extraction. Experimental milling systems,

such as the Storamil process, have given 65–75%

yields of fine flour. Pearling or debranning of pearl

millet has also been achieved with a vertical cone

polisher of the type normally used for polishing rice.

0010 Pearl millet can be malted and used wholly or

partially in place of sorghum malt in the traditional

or industrial brewing of opaque beer. However, the

small size of the grain is a disadvantage in large-scale

industrial malting plants.

0011 Pearl millet is also grown as a forage crop in the

southeastern USA and in some parts of southern

Africa.

Finger Millet

0012 Finger millet (Eleucine coracana (L.) Gaertn, ssp.

coracana) is commonly known as ragi in India and

wimbe in East Africa; these are the major finger-

millet-growing areas. Common English names are

African millet, birdsfoot, and coracana.

0013 Finger millet was developed in Africa from

E. coracana ssp. africana, probably in the Ethiopian

region. It was introduced to India perhaps more than

3000 years ago. It is a tropical crop grown from sea

level to 3000 m above sea level.

0014 The global production of finger millet is about

3.7 10

t of grain per year with an average of

0.6 t of grain per hectare. The improved varieties

under good management can produce up to 4 t of

grain per hectare. In Asia, the major finger-millet-

producing country is India (2 613 000 t), followed by

Nepal (122 000 t), China (79 000 t), and Afghanistan

(38 000 t). In Africa, Uganda ranks first (451 000 t),

followed by Ethiopia (198 000 t), Tanzania (95 000 t),

and Zimbabwe (46 000 t). To a lesser extent, it is

also grown in many other countries, such as Iran,

Sri Lanka, Myanmar, Bhutan, Iraq, Pakistan, and

Jordan, and (in Africa) Kenya, Burundi, Zambia,

eastern Zaire, Sudan, Malawi, South Africa, and

Rwanda.

0015Plants are annual, tufted, erect, or with genicu-

lately ascending culms; they reach an average height

of 103 cm and a maximum height of 165 cm, and they

sometimes root from the lower nodes. Culms are

commonly branched from the upper nodes to produce

secondary inflorescences. Leaf blades are linear to

linear-lanceolate, generally 35 cm but sometimes up

to 70 cm in length, and 20 mm wide. Inflorescences

are digitate, often with one or more racemes some

distance below the main cluster of four to 19

branches. Inflorescence branches are slender, or in-

curved at the tip when robust, sometimes with sec-

ondary branches. Spikelets are six- to nine-flowered

and 6–10 mm long, overlapping, and mostly arranged

in two rows along one side of the rachis. Glumes are

unequal and shorter than the spikelet. The inflores-

cence shape is variable. The digitately arranged

branches may spread out and become reflexed, or

they may be erect and incurved, often forming a fist-

like structure.

0016Finger millet is largely a peasant crop. Seeds vary in

color from light brown to dark brown or purple, and

are small, up to 2 mm long, globose, and hard. The

individual seed weight can vary from 1 to 3 mg. The

small, flinty grains are highly resistant to both stored

insect pests and molds, and thus have excellent stor-

ability. Some of the brown finger millet varieties con-

tain high levels of tannin – 3–4% catechin equivalent.

(See Tannins and Polyphenols.)

Processing and Food Use

0017Immature grain is roasted green and consumed in

the dough stage. Traditionally, the grain is processed

by wet grinding on stones. The resulting flour is dried

and consumed as thick or thin porridge. Light-

colored millets are particularly well suited for

malting, the diastatic activity of millets (except pearl

millet) being higher than that of sorghum. One of the

major uses of finger millet in Africa is therefore in

malting, prior to the brewing of traditional beers. To

a limited extent, finger millet is reported to be grown

in Japan and China, where its major use is the making

of beer. In India, and Sri Lanka, finger millet flour is

used in the preparation of unleavened bread (roti).

(See Sorghum.)

0018Advantageous nutritional attributes of finger millet

are its particularly high calcium and iron contents

3976 MILLETS

(220–855 mg per 100 g and 64–15 mg per 100 g,

respectively) and its high methionine content

(83–226 mg per gram total N). In Nepal and India,

farmers attach economic value to finger millet straw,

since they use it as a livestock feed.

0019 Processing of finger millet by dehusking or debran-

ning was unsuccessful because of the small seed size,

the relatively thick pericarp, and a highly friable

endosperm. Roller milling of whole grain and sieving,

however, produces a refined flour. Similarly, in trad-

itional processing, finger millet is ground or pounded

to a flour as whole grain, and particles of pericarp are

sifted or winnowed out. (See Flour: Roller Milling

Operations.)

0020 In the preparation of unleavened breads such as

roti or chapati, a cold-water dough does not hold

together owing to the lack of gluten. Hot water is

therefore used to pregelatinize the starch and to attain

the required degree of cohesiveness for preparing the

thin, flat, griddle breads. (See Chapatis and Related

Products.)

Foxtail Millet

0021 Foxtail millet (Setaria italica (L.) P. Beauv.) is also

known as Italian millet and setaria. It is grown as

a cereal in southern Europe, and in temperate,

subtropical, and tropical Asia. It was domesticated

in the highlands of central China around 5000 years

ago, and spread to Europe and Asia soon after its

domestication.

0022 Total production of foxtail millet is around

5.7 10

t of grain per year, of which China alone

produces 4.9 10

t, followed by India (500 000 t).

It is also grown in Europe, particularly in Portugal,

Turkey, Hungary, France and Spain, in Asia, primar-

ily in Korea, Pakistan, Myanmar, Bhutan, Nepal, and

South Africa. Each of these countries produces less

than 10 000 t per year.

0023 There are three morphologically distinct races:

moharia, maxima, and indica. These differ in mor-

phological characteristics, such as plant height and

inflorescence, as well as in distribution. Race moharia

is cultivated in southeastern Russia, Afghanistan, and

Pakistan. Race maxima is cultivated in transcauca-

sian Russia, the Far East, and the USA for bird feed.

Race indica is largely cultivated in India and southern

Asia.

0024 Cultivars from India are morphologically different

from those of Europe and the Far East, and are

typically robust with inflorescences bearing branches

loosely arranged on the primary axis.

0025 Variability has been reported for several

characteristics such as plant height (20–175 cm),

peduncle length (0–500 mm), inflorescence length

(10–320 mm), exertion (10–360 mm), basal tillers

(1–80), and in time to flowering (30–135 days) in

germplasm accessions.

Uses

0026Foxtail millet is widely used as a food grain and as a

forage crop in Asia, North Africa, and southeast

Europe. It is used for brewing beer in Russia and is

an important food crop in China, where it is used in

gruels, for making cakes, and in beer and vinegar

production. It is also used as a medicinal food in

Chinese medicine, the beneficial effects being partly

attributable to its high nutritional quality. The grain

is also used as an animal feed, and the straw as forage.

Proso Millet

0027The millet with the botanical name of Panicum mili-

aceum (L.) is known as proso millet in Russia.

0028The common English names of this millet are hog

millet, common millet, and broomcorn millet. The

progenitor of proso millet is native to Manchuria. It

was probably domesticated in central and eastern

Asia, and was cultivated in Europe in Neolithic

times. The species was introduced to Europe as a

cereal at least 3000 years ago. This is essentially a

crop of the temperature regions, but it is also grown

in the subtropics and on high ground in tropical

winters.

0029Proso ranks third after pearl millet and foxtail

millet in terms of total global millet production,

about 5 10

t of grain per year. The major proso-

millet-producing countries are the Commonwealth of

Independent States (2 330 000 t), China (1 600 000 t),

India (500 000 t), Argentina (173 000 t), Myanmar

(150 000 t), and the USA (110 000 t). It is also

grown on small acreages in Korea, Australia, Turkey,

Austria, Yugoslavia (Montenegro, Serbia), Pakistan,

Greece, Bhutan, Nepal, Mongolia, and Japan.

0030Plant height varies from 25 to 133 cm. The inflores-

cence length varies from 2.2 to 40 cm. The flag leaf

may cover as much as 5 cm of the inflorescence; how-

ever, the exertion of the inflorescence may be up to

32 cm. This is a highly tillering crop. It is early matur-

ing, some of the accessions flower in 28 days, and a

crop can be harvested in 50–55 days. However, most

of the accessions flower in 30–35 days, and a few take

up to 50 days. The individual seed weight can vary

from 5 to 9 mg – similar to that of pearl millet. It is a

self-pollinated crop, and hybridization can be

achieved by hand emasculation.

Food Uses

0031In China, the grain is steamed or boiled like rice. It is

also eaten flaked and sweetened with sugar. In the

MILLETS 3977

USA, it is the largest millet crop and is largely used as

a feed grain. Proso millet has been comilled in an

experimental, semiindustrial process with wheat

after individually conditioning the grains to 16%

moisture. The flour can be used at up to 10% add-

ition rates with no deleterious effects on the quality of

bread.

Kodo Millet

0032 Kodo millet (Paspalum scorbiculatum L.) is also

known as ditch millet. It is grown only in India,

although the wild grass is a widespread tropical

weed that is harvested as a wild cereal in West Africa.

The species was domesticated in India some 3000

years ago. It is grown in India from Kerala and

Tamil Nadu in the south, to Rajasthan and Uttar

Pradesh in the north, and West Bengal in the east, as

a food grain.

0033 The plant height can vary from 30 to 90 cm, with

10–48 basal tillers per plant. The length of the inflor-

escence varies from 2 to 12 cm. It is a relatively late-

maturing crop compared to other small millets. The

flowers are highly cleistogamous with a maximum

opening of up to 50% only, i.e., this is a highly

self-pollinated crop. Cytological studies have

revealed the chromosome number as 2n ¼40.

0034 The statistics for kodo, little, and barnyard millets

are combined together, and these species are grown

only in India, except barnyard millet, which is also

grown in Japan (only 1000 t per year). The total

production in India is around 386 000 t per year.

0035 The crop is hardy and drought-resistant, and is

capable of growing in marginal soils. The grain is

enclosed in a hard, corneous husk, which makes

debranning difficult. The grain is said to be poisonous

after rain; this may be due to a fungal infection.

Winnowed, clean, healthy grain seems to pose no

health problem. Kodo millet is primarily cooked as

rice.

Little Millet

0036 Little millet (Panicum sumatrense Roth. ex Roem. &

Schult.) is also known as miliare. It is widely culti-

vated as a cereal across India, Nepal, and western

Myanmar. It is particularly important in the eastern

ghats of India, where it forms an important part of

tribal agriculture.

0037 A comparative morphological study of accessions

resulted in the recognition of two races. Race nana

plants are small (60 cm) to large (170 cm) with de-

cumbent culms that root at the lower nodes before

becoming erect to produce flowering culms. Terminal

inflorescences are 14–50 cm long, erect, open, and

strongly branched, with the branches sometimes

clumped at the time of maturity. Race robusta in-

cludes plants that are erect, or produce flowering

culms from a shortly geniculate base. Flowering

culms are 120–190 cm tall and robust. Terminal in-

florescences are 20–46 cm long, open, or compact

and strongly branched. Open inflorescences are es-

sentially erect, and compact inflorescences become

curved at maturity. It is largely a selfpollinated crop;

natural cross-pollination can occur up to 3.5%.

0038The dehusked grain is cooked and consumed like

rice, or is milled into flour. The crop thrives under

conditions that will sustain no other edible plant and

will mature in 2–5 months.

Barnyard Millet

0039Japanese barnyard millet (Echinochloa crusgalli)is

native to temperate Eurasia and was domesticated in

Japan some 4000 years ago. Barnyard (sawa) millet

(E. colona) is widely distributed in the tropics and

subtropics of the Old World, and was domesticated

in India. The two species have different chromosome

numbers (2n ¼54 and 2n ¼36, respectively), and

hybrids between them are sterile.

0040Cultivated plants of E. colona (L.) Link. are erect

or geniculate ascending, often tufted, annual, and

up to 242 cm tall. Culms are slender to robust.

Slender plants are decumbent, with the culms

strongly branched and rooting from the lower

nodes. Stout plants are erect, with a few culm

branches from the upper nodes. Inflorescences are

variable; decumbent plants are characterized by

short racemes that are appressed to the primary

axis, whereas more robust plants have larger, pyram-

idal inflorescences with spreading lower racemes. In-

florescences are usually erect, rarely drooping, and

can be up to 28 cm long. Spikelets are persistent at

maturity, 2–4 mm long, acute but never awned. The

grain is 2–3 mm long and 1–2 mm wide.

0041Cultivated plants of E. crusgalli (L.) P. Beauv. are

erect, tufted, annual and up to 100 cm tall. Culms are

mostly robust, simple, or branched from the upper

nodes. Inflorescences are erect or slightly nodding,

well exertion from the upper leaf sheath, with the

spike-like racemes more or less erect and sometimes

incurved at the tip. Spikelets are persistent at matur-

ity, very crowded, 3–4 mm long, shortly cuspidate but

rarely awned. The grain is 2–3 mm long and almost as

wide.

0042Japanese barnyard millet is the fastest maturing of

the millets and, under favorable temperature and

moisture conditions, ripens within 45 days. The crop

is grown for forage and food in India, and in the USA

is said to produce two harvests within the cropping

3978 MILLETS

season. Echinochloa decompositum, the Australian

variety is used as food by aboriginal tribes.

Teff

0043 Teff (Eragrostis tef) is the most important cereal crop

in Ethiopia, particularly in the poorly drained, heavy

soils that predominate in the Central Plateau. The

total production is slightly above 1 10

t per year.

Ethiopia is considered the center of origin of the crop,

and domestication is thought to have started in the

northern highlands. Teff grows in Australia, Kenya,

and South Africa, but is cultivated as a major staple

crop only in Ethiopia.

0044 Teff is cultivated from sea level to 2800 m, on soils

varying from waterlogged to well drained, and in

areas that have less than 300 mm or more than

1000 mm seasonal rainfall.

0045 Teff is a sexually propagated, self-pollinated

annual tufted grass. It is an allotetraploid with

2n ¼40 chromosomes. The plants are short in stature

(height varying from 45 to 150 cm) with loose, open

panicles. The culm thickness varies from 1.2 to

3.1 cm. Teff can mature in 3–4 months, but a few

early-maturing accessions can mature in 2 months.

The average grain yield is 0.8 t ha

1

, but with

improved management and cultivars, up to 2 t ha

1

can be obtained.

0046 Two types of teff are found in Ethiopia – white- and

brown-seeded varieties – and the white is preferred

for food. The grain is very small, about 1–1.5 mm in

length, and 1000 grains weigh approximately 0.3 g.

0047 The flour of teff is used in Ethiopia for making a

flat, fermented, griddle bread or pancake known as

injera. It is also used for making porridge and the

traditional alcoholic drinks, ‘tella’ and ‘katikalla.’

Fonio

0048 Fonio (Digitaria exilis Stapf) is also known as ‘hungry

millet,’‘hungry rice,’ fundi, and acha. It is grown

throughout the savanna areas of west Africa, notably

in Guinea and Nigeria. The crop is not cultivated

outside Africa and is capable of thriving in poor,

rocky, and marginal soils. It is considered to be the

oldest West African cereal, and its cultivation is

thought to date back to 5000 bc. Black fonio

(D. iburua Stapf) is grown by the Hausa of Nigeria

(northern Nigeria), and in Guinea, Togo, and Benin,

but the total production of black fonio is insignifi-

cant.

0049 Total production of Fonio is 309 000 t per year, and

about 70% of this is produced in Guinea (200 000 t).

The other major producing areas are Nigeria

(58 000 t) and Mali (36 000 t). To a lesser extent, it

is also grown in Burkina Faso, Ivory Coast, Niger,

and Gambia. It is grown on the plains as well as in the

mountains, i.e., under annual rainfalls from 400 to

3000 mm.

0050Fonio is an annual plant with a plant height of 45–

50 cm. The roots are well developed and attached

firmly to the soil. The inflorescence is composed of

two to six fingers of 5–12.5 cm length. The grains are

small, and the individual grain weight is 0.5–0.6 mg.

The grain yield varies from 0.2 to 0.5 t ha

1

. In low-

rainfall areas, the crop matures in 2–4 months,

whereas in high-rainfall areas, the maturity period

varies from 4 to 5 months.

0051The seed is very small and is usually threshed and

pounded to remove chaff; it is used alone or mixed

with other cereals to make porridge. The grain can

be added to stews, or boiled and eaten with palm

oil. Fonio can also be used for brewing beer. In com-

parison with other cereals, fonio has a poor nutri-

tional value in terms of total protein and amino-acid

balance.

See also: Cereals: Contribution to the Diet; Dietary

Importance; Chapatis and Related Products;

Fermented Foods: Beverages from Sorghum and Millet;

Flour: Roller Milling Operations; Goitrogens and

Antithyroid Compounds; Sorghum; Tannins and

Polyphenols

Further Reading

FAO (1990) Structure and Characteristics of the World

Millet Economy. CCP:GR 90/4, July 1990. Rome:

Food and Agriculture Organization.

Hulse JH, Laing EM and Pearson OE (1980) Sorghum and

the Millets: Their Composition and Nutritional Value.

London: Academic Press.

Krishna Kumari S and Thayumanavan B (1998) Character-

ization of starches of proso, foxtail, barnyard, kodo, and

little millets. Plant Foods for Human Nutrition 53(1):

47–56.

Pathak P, Srivastava S and Groves S (2000) Development of

food products based on millets, legumes and fenugreek

seeds and their suitability in the diabetic diet. Inter-

national Journal of Food Science and Nutrition 51(5):

409–414.

Prasada Rao KE, de Wet JMJ, Gopal Reddy V and Menge-

sha MH (1991) Diversity in the Small Millets Collection

at ICRISAT. Paper Presented at the Second International

Small Millets Workshop, 8–12 April 1991, Bulawayo,

Zimbabwe.

Seetharam A, Riley KW and Harinarayana G (eds) (1989)

Small Millets in Global Agriculture. Proceedings of the

First International Small Millets Workshop, Bangalore,

India, October 29–November 2, 1986. New Delhi:

Oxford and IBH Publishing.

MILLETS 3979

MILLING

Contents

Principles of Milling

Types of Mill and Their Uses

Characteristics of Milled Products

Principles Of Milling

E S Posner, ESP International, Savyon, Israel

Introduction

0001 The wheat seed which is used for the manufacture of

flour is an elongated structure 7–12 mm long and 2–

4 mm wide (Figure 1). A crease along the kernel

extends nearly to the center. Structurally, the wheat

kernel consists of three main parts. The pericarp is the

outer coat and is divided into several layers. The

wheat germ is divided into the embryo and the scutel-

lum. The endosperm is an accumulation of cells that

makes up to 83% of the kernel. The endosperm cells,

which are the ‘flour’ when reduced to small particles,

contain many starch granules embedded in a protein-

aceous matrix. (See Wheat: The Crop.)

0002 Wheat is a living organism which varies in its qual-

ity as a result of genetic characteristics as well as

a result of growing and storage conditions. Wheat-

processing characteristics are related to its millability,

protein quality and quantity, and baking results of the

end product. Three main kinds of wheat can be rec-

ognized: hard, soft, and durum. Hard wheats tend to

be higher in protein content (10–15%), usually have

harder structured endosperm, and find their principal

use in bread flour. Flour produced from internally

softer wheats, with lower protein content (8–11%),

are used in cake and cookie production. Durum

wheats are processed to a granular or floury endo-

sperm product for pasta. Distinctively different

milling systems are designed to accommodate the

differences in wheat that affect their millability. Al-

though in the past mills were usually constructed to

mill the locally harvested wheat, modern mills in any

part of the world can be designed to process any

desired wheat for a special end product.

0003 The wheat flour-milling operation consists of the

following functions: receiving, analyzing, wheat stor-

age, blending, cleaning, conditioning, milling, prod-

uct storage, and shipping. Table 1 indicates the

various products and byproducts of the wheat-milling

operation.

Wheat Quality for Milling

0004The determination of wheat milling quality is very

complex. No single test has yet been devised to estab-

lish conclusively the milling quality of a wheat. Fluc-

tuations in wheat characteristics and quality reduce

the efficiency of the fully automated, high-capacity

milling unit of today. High moisture replaces the

amount of dry material in the wheat and is a signifi-

cant economical quality factor. Larger wheat kernels

are correlated with potential flour yield. Smaller

kernels have a larger ratio between pericarp and

endosperm, resulting in a lower amount of available

endosperm. The weight of a thousand sound, whole

wheat kernels, corrected to a fixed moisture level,

is also a good indication of the flour yield and

millability. Hardness of the kernel, especially after

it has been tempered for milling, is an important

quality characteristic. Harder wheats require longer

tempering stages and produce more granular mater-

ial, which flows and sieves better. Harder wheats also

tend to give better extraction levels as a result of

better separation of endosperm from bran. All the

above-mentioned kernel characteristics affect the

milling quality of wheat and require the appropriate

design of a milling system and its adjustment. Recent

development of the single-kernel characterization

system (SKCS) can be calibrated to measure single-

kernel hardness, protein, starch, internal insect infest-

ation, color, disease, size, and moisture.

Wheat Storage and Blending

0005Wheat storage involves a substantial investment in

facilities, equipment, and the value of the stored

wheat. Different means of preservation are used,

such as aeration with ambient air of the right charac-

teristics or cooled air, fumigation, and control

systems to monitor any physical or chemical changes

in the wheat. Uncontrolled storage conditions could

cause wheat deterioration, starting in ‘pockets’ in the

bin as a result of high moisture. Live insects would

also flourish if the temperature, humidity and grain

fractions were readily available. There is an equilib-

rium between moisture content of the wheat, air

3980 MILLING/Principles Of Milling

temperature, and humidity. Accordingly, safe storage

conditions include a moisture content below 12.5%,

and temperature below 25



C. Even under optimal

conditions, stored wheat goes through a continuous

change in its milling and baking characteristics by

aging; this change is significant in the 3 months im-

mediately after harvest. (See Controlled-atmosphere

Storage: Applications for Bulk Storage of Foodstuffs;

Insect Pests: Problems Caused by Insects and Mites.)

0006One of the miller’s main objectives is to be a sup-

plier of uniform product to the customer. To accom-

plish this, there must be on hand wheats with such

qualities that blending them will produce a mill-grist

that is uniform in all its physical and chemical char-

acteristics. To accommodate this need, it is important

to evaluate wheat upon receipt and segregate it in bins

according to quality.

tbl0001 Table 1 Products from a milling system

Product Percentage

of total

Primary end use

Wheat screenings

1–3 Feed

Flour I 60–65 Baked products

Flour II 10–17 Baking, industrial utilization

Farina 3–8 Breakfast foods

Semolina

65–67 Pasta

Bran

22–25 Feed, high-fiber

Germ 0.2–0.5 Food, cosmetics

Based on wheat entering the mill.

Screenings are impurities removed from wheat before grinding.

In durum milling, only the rest (8–10%) of extracted endosperm is flour II.

Bran is a distinct byproduct consisting of broad pericarp flakes, the

aleurone layer, and some endosperm. Commercially, the term includes all

offals from the process, such as the shorts (fine bran, germ, and

endosperm particles) and red dog (very fine bran, germ, and endosperm

particles).

Hairs of

brush

Endosperm

Cell filled with

starch granules

in protein

matrix

Cellulose walls

of cells

Aleurone cell layer

(part of endosperm but

separated with bran)

Nucellar tissue

Seed coat (testa)

Tube cells

Cross cells

Hypodermis

Epidermis

Scutellum

Sheath of shoot

Rudimentary shoot

Rudimentary

primary root

Root sheath

Root cap

Crease

Endosperm

Pigment

strand

Bran

Germ

(a)

(b)

fig0001 Figure 1 (a) Longitudinal section (enlarged about 33 times) and (b) cross-section of the wheat kernel. The endosperm makes up

about 83% of the kernel, the bran about 14.5%, and the germ about 2.5%. Courtesy of the Wheat Flour Institute, Washington DC, USA.

MILLING/Principles Of Milling 3981

Wheat Cleaning

0007 The current methods of wheat harvesting make it

impossible to obtain a pure product off the field.

Foreign materials in the grain bulk have to be

removed before milling, and this is accomplished

in the wheat-cleaning section.

0008 Separation of the unmillable fractions from wheat

is based on differences in the following material char-

acteristics: size, specific weight, shape, color, solubil-

ity, and response to magnetic forces. Many versions

and combinations of those principles have been com-

bined in cleaning machines. Modern equipment com-

bines more than one principle so that, in many cases,

the bulk of the grain in a certain range of size and

specific weight is diverted to subsequent stages in the

process, whereas only a small part of the load is

cleaned intensively.

Wheat Conditioning

0009 The clean wheat is subjected to the conditioning pro-

cess, which is the addition of water followed by a time

period of tempering it, allowing the water to be

absorbed by the kernels. The objective in condition-

ing the wheat before milling is to reach a state at

which the pericarp and germ parts are tough and

plastic and do not splinter during the grinding

process, because they absorb water very readily.

On the other hand, the endosperm should be as

friable as possible. Three variables effect the condi-

tioning process, namely tempering time, temperature,

and moisture.

0010 Characteristics such as internal structure and level

of pericarp damage of the wheat kernel exert different

effects on the conditioning of wheat for milling.

Wheat size significantly affects the water penetration

rate because of its relationship to the specific surface

area of the kernels. The relative best tempering time

is the period that allows the bulk of the wheat to

reach the optimum equilibrium of water penetration

into all kernels. Uncontrolled moisture fluctuations

in wheat fed to the fully automated mill might

cause operational problems, as well as change in

flour quality.

Wheat-Milling Process

0011 The objective of the flour-milling process is initially

to separate the major botanical parts of the wheat

kernel – the endosperm, the pericarp, and the germ

– from each other. Subsequently, it reduces the endo-

sperm to finely ground flour, which passes through a

sieve with an aperture of not larger than about

200 mm. From the technical aspect of flour milling,

the efficiency is weighed mainly by the level of separ-

ation among those parts, and production of a high

percentage of flour with a relatively low contamin-

ation with germ and pericarp parts. The miller’s

objective is to produce flour with good color, and

products which have not deteriorated to an unex-

pected level during the milling process. The practical

miller, for example, would count on about 1% reduc-

tion of protein between the whole wheat and the

resulting flour, when using wheat in the range of

10–13% protein.

0012The current basic concept of the wheat-milling

process was established at the end of the nineteenth

century, when iron rollers were applied instead of

grinding stones. The wheat is ground between two

rollers which rotate against each other and are pos-

itioned horizontally in a rollermill machine. The com-

mercial grinding rollers dimensions range from 180 to

350 mm in diameter and up to 1500 mm in length.

From a performance point of view, smaller-diameter

rollers are more fitted to those stages in which the

objective is a shearing action to separate the endo-

sperm from the bran. On the other hand, larger-

diameter rollers create a longer grinding path that

acts on the material, mainly through compression.

Most modern wheat mills have rollers that are of

the same length and diameter to achieve maximum

uniformity and avoid keeping a large inventory of

spare rollers. (See Flour: Roller Milling Operations.)

0013The outer layer of the cast-iron rollers, about

13 mm thick, is harder than the inner core; the casting

process is responsible for this. Frequently, the rollers

are called ‘chills’ because they undergo a cooling

process. Fast cooling after casting will keep the

carbon mixed evenly with the steel and create a hard

surface. Slow cooling will allow the carbon in the

steel to crystallize, which will result in a softer surface.

To extend the duration of the corrugations’ sharp-

ness, the harder-surface rollers are used. In the

smooth rollers, made out of softer steel, the carbon

crystals that are dissipated during the wearing of

the surface cause it to stay rough and grip the endo-

sperm particles better, causing an effective reduction

to flour.

0014Mill designers use a specific and cumulative roller

length in the design of a certain milling process. As an

example, a mill will be designed based on a total of

18 mm roller length per 100 kg wheat per 24 h. Re-

cently, improved machine design has reduced sub-

stantially specific roller length. Automation and

high-efficiency roll bearings contribute to the ability

to run the rollermill machine at a speed higher than

previously. The first grinding stages in the mill,

known as ‘breaks,’ ideally open the kernel and scrape

off the endosperm from the bran. Subsequently,

3982 MILLING/Principles Of Milling

smooth ‘sizing’ and ‘reduction’ rollers are used to

downsize endosperm granules to fine flour. The sur-

face of the breaking rollers is corrugated along the

axis. There are fewer corrugations per centimeter in

the head breaks and they increase in number to the

last break. The number of corrugations per centi-

meter ranges from four to 10 in the breaks. The

corrugations are cut in spiral, relative to the axis of

the roller, ranging from 8% to 18% (4



). A large spiral is responsible for more flour,

whereas a smaller spiral generates more granular

endosperm particles. The spirals cross in a scissor-

like fashion when the rollers are rotating against

each other. A single corrugation has a front angle

and a back angle, which creates a sharper edge and

a duller edge respectively (Figure 2). By rotating the

rolls at different speed (differential of 2.5:1) against

each other, the main effect is a shearing action of the

surfaces against each other. The front angle (‘sharp’

edge) or back angle (‘dull’ edge) of one roll acts

against the ‘sharp’ or ‘dull’ edge of the other roller

(Figure 3). There is also a compression effect, but it is

very carefully controlled just to open the kernel and

release the endosperm.

0015 Between the reduction rollers, there is a differential

of ratios 1.2:1 to 1.5:1. The lower differential is

responsible for a larger compression effect on the

material. Smooth rollers are set closer to reduce

endosperm chunks to flour and, as a result, they

require considerably more power than corrugated

rollers. The miller controls the compression between

the rollers to avoid extensive damage to the flour and

prevent excessive flacking of the endosperm

particles. Flacked endosperm might also cause flour

extraction loss because the tailover from the top

sieves in the reduction sieving sections end up in the

tailover streams of the mill and, subsequently in

the bran (stock that has gone over a sieve is known

as ‘overs’).

0016The heterogeneous material after each stage of the

grinding rollers is sent to a sieving machine called

‘plansifter’. This is an enclosed unit in which up to

10 stacks or compartments, of up to 32 sieve frames,

are placed. The exact number of frames depends on

the materials sieved and on the manufacturer

involved. The machine is centrifugally balanced and

rotates at a certain prescribed number of rotations per

minute and at a definite ‘throw,’ or radius. In a sifter

compartment, sieves are arranged in groups which

differ in their aperture size. Sieve aperture (measured

in microns) is determined by the miller. The mill

designer allocates a certain sieving surface area to

each granulation of the material entering each sieving

stack. Tailover materials from the sieves are directed

to the next stage in the process for further grinding or

purification. A certain percentage of flour is extracted

from each of the sieving stages in the mill.

0017Purification is one of the three major processing

principles in the flour milling process. The purifier is

a machine in which air currents are drawn through

one to three layers of sieves, and the sieves move

simultaneously in a reciprocating motion (Figure 4).

The material fed to the purifiers is made up of par-

ticles of about the same size range but differing in

their content of endosperm and bran. The differences

in relative density between pure endosperm (about

1.44 g cm

3

) and pure bran coat or pericarp (about

1.22 g cm

3

) are used in the purification process.

Stratification with the help of the controlled air cur-

rents occurs between the heavier particles of relatively

fig0002 Figure 2 Roll corrugation: a front angle; b back angle.

(a) (b) (c) (d)

fig0003 Figure 3 Roll disposition: S, sharp edge: D, dull edge of a corrugation. (a) sharp to sharp: (b) dull to dull; (c) sharp to dull; (d) dull to

sharp.

MILLING/Principles Of Milling 3983