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such as peas and carrots. These products are similar

to snack foods in that the starch must be well dis-

persed to give good expansion and a light texture.

The process must be controlled in terms of tempera-

ture to keep the mass temperature as low as possible

<130



C during processing.

0035 The second form of baby foods is more important

because it represents a larger amount of production.

It was developed to match the roller-dried instant

baby food, which is consumed as a porridge, prepared

by mixing water or milk with a dry instant powder.

The extruded product is made by processing a feed-

stock of cereals with milk solids under conditions of

medium shear input and controlled temperature. The

aims are to melt the starch granules, but to retain

their structures to a large extent. This gives a high

paste viscosity when added to water or milk and

produces a more attractive porridge. It is also import-

ant to control the temperature of the fluid to reduce

any browning reactions that would discolor the prod-

ucts and reduce the nutritional quality of the proteins.

See also: Cereals: Breakfast Cereals; Extrusion

Cooking: Chemical and Nutritional Changes; Infant

Foods: Weaning Foods; Snack Foods: Dietary

Importance

Further Reading

Chang YK and Wang S (eds) (1996) Advances in Extrusion

Technology, Aquaculture/Animal Feeds and Foods.

Lancaster, PA: Technomic.

Frame N (ed.) (1994) The Technology of Extrusion Cooking.

Glasgow, UK: Blackies, Academic & Professional.

Guy RCE (ed.) (2001) Extrusion Cooking, Principles and

Technologies. Cambridge, UK: Woodhead Publishing.

Kokini JL, Ho C-T and Karwe MV (eds) (1991) Food

Extrusion Science and Technology. New York: Marcel

Dekker.

Mercier C, Linko P and Harper JM (eds) (1990) Extrusion

Cooking. St. Paul, MN: American Association of Cereal

Chemists.

Chemical and Nutritional

Changes

I T Johnson, Institute of Food Research, Norwich, UK

Background

0001 The extraordinary versatility of the extrusion

cooking process and its variants has led to the use of

this technology in a very wide range of applications

by the food-processing industry. In developed coun-

tries it is widely employed to fabricate snack foods

with novel characteristics of flavor and texture, but

which usually have little nutritional significance in

the diet as a whole. However, the technique can also

be applied to the production of more substantial

products such as breakfast cereals and crispbreads

and even weaning foods, which may contribute a

very large proportion of the total nutrient intake of

infants. Even in the developing world, where a suit-

able technical environment exists, extrusion cooking

may be applied to the production of staple foods from

indigenous crops. This remarkable variety of applica-

tions is a direct result of the extreme physical condi-

tions which the process imposes upon raw materials,

and the complex transformations which are achieved

in the final product. The chemical and physical reac-

tions which underlie these changes can have both

positive and negative implications for nutrition

and food safety. This issue has attracted increasing

attention in recent years.

Changes in Carbohydrates

0002Cereals and potatoes were the first commodities to be

widely processed by extrusion cooking, and they are

still the most common. This fact has helped to focus

particular attention on the behavior of complex

carbohydrates during high-temperature extrusion.

Cereal grains and vegetable tubers are storage organs

which contain starch, and some free sugars, embed-

ded within a complex cellular matrix. Starch consists

of glucose molecules, linked in the case of amylose

exclusively by a-1,4 bonds, or, in the case of amylo-

pectin, by a combination of a-1,4 and a-1,6 bonds,

which give a branching structure to the molecule. All

such links are susceptible to hydrolysis by the digest-

ive enzymes of the human alimentary tract. Cell walls

are much more complex structures containing a

variety of different polysaccharides, all of which are

resistant to digestion. These materials, together with

lignin, comprise dietary fiber. (See Carbohydrates:

Interactions with Other Food Components; Dietary

Fiber: Properties and Sources; Lignin; Starch: Struc-

ture, Properties, and Determination.)

0003Native, uncooked starch also resists digestion

because it is localized within plant cells in the form

of semicrystalline granules containing varying pro-

portions of amylose and amylopectin. The polysac-

charides are tightly bound together by hydrogen

bonding, but the density and orderliness of the

bonding vary within the granule matrix. In the pres-

ence of moisture, hydrogen bonding in the less

ordered regions of the granule is susceptible to

EXTRUSION COOKING/Chemical and Nutritional Changes 2227

disruption by heat. This allows the entry of water into

the granule, which then swells and becomes in-

creasingly susceptible to mobilization and dispersion

of its constituent polysaccharides. Where substantial

quantities of excess water are present, the granular

structure of starch is completely converted into

a viscous fluid dispersion. This process is called gel-

atinization and it is one of the most important func-

tions of processing and cooking because it renders

starch readily available for digestion in the small

intestine.

0004 During the extrusion cooking process a dough is

driven continuously through a die by one or more

screws rotating within a high-pressure barrel. As the

dough is pressurized its temperature rises. An external

source of heat may also be employed, and working

temperatures ranging from 100 to 180



C are com-

monly achieved. When the dough emerges from the

die, the sudden fall in pressure causes rapid expansion

and instantaneous generation of steam. Thus, the

extrusion cooking process is characteristically one in

which high temperature, pressure, and shear forces

are imposed upon a starch-rich matrix, which has a

relatively low water content, for a short time. All of

these conditions are varied at will by the processor, in

striving to optimize the texture and other properties

of the final product.

0005 There have been numerous empirical investigations

of starch behavior during extrusion under different

conditions, but no completely adequate theoretical

account has been developed. Nevertheless, some

useful generalizations are possible. Under low-mois-

ture conditions, starch granules degrade or melt at a

temperature higher than that of conventional gelatin-

ization. This process can take place within the high-

temperature environment of the extruder barrel. The

high pressures and shear stresses of extrusion cooking

increase the efficiency of gelatinization so that fin-

ished products often possess a completely amorphous

and hence readily digestible starch matrix, which

nevertheless has a very low water content. Moreover,

it is not only starch granules which are degraded

under extreme extrusion conditions. Scanning elec-

tron micrographs of cereal grains such as maize

demonstrate a loss of structural organization within

the extruded tissue, and an apparent absence of intact

cell walls.

0006 One of the most important attributes of dietary

fiber is the structural organization which it confers

upon lightly processed plant foods. There is strong

evidence that intact cell walls tend to encapsulate

gelatinized starch granules in conventionally cooked

foods, and thereby slow the access of pancreatic

enzymes so that starch digestion is delayed. This

leads to a relatively slow rate of glucose absorption

and an attenuation of the peaks and troughs of blood

glucose which occur after meals. In studies with

human volunteers, test meals consisting of breads

processed by extrusion cooking have been shown to

be more rapidly digested than conventionally cooked

breads. The principal aim in the dietary management

of diabetes mellitus is the maintenance of blood

glucose at levels as close as possible to the normal

range, and it has been suggested that diabetics should

avoid extruded cereal products and snack foods.

However, this principle has not been fully confirmed

in patients consuming mixed diets over a long period

of time, and there is little or no evidence that such

relatively minor differences in carbohydrate availabil-

ity are of any nutritional significance in healthy

subjects.

0007Apart from the disruption of cell walls, dietary

fiber also undergoes chemical changes during extru-

sion cooking. Under relatively mild conditions the

total fiber content of extruded wheat flour remains

more or less constant, but there is some increase in the

soluble fiber content at the expense of insoluble fiber.

Under more severe conditions a moderate increase in

total fiber content has been reported. Clearly, this

material is not true dietary fiber in the sense of

cell wall polysaccharides. It probably represents a

combination of Maillard reaction products and amy-

lose-resistant starch complexes. The physiological

significance of these substances is unknown, and

they may be best regarded as artifacts.

Interaction of Protein and Carbohydrates

0008Under extreme extrusion conditions the disruption of

complex carbohydrates extends to the molecular

level. A proportion of the starch may be hydrolyzed

to release glucose which then becomes available for

further chemical reactions within the extruder. The

most important of these is the Maillard reaction

which occurs between reducing sugars and the free

amino group of lysine, and gives rise to a very com-

plex family of ‘browning products.’ Such compounds

alter the flavor and color of the finished product and

are responsible for many of the organoleptic conse-

quences of cooking. However, Maillard reaction

products are usually indigestible and, since lysine is

an essential amino acid, any such loss of bioavailabil-

ity has an adverse effect on the nutritional quality of

protein. (See Protein: Interactions and Reactions

Involved in Food Processing.)

0009The extent of lysine loss in extruded products

depends upon the extrusion parameters and the com-

position of the dough. In general the biological avail-

ability of lysine is markedly reduced at temperatures

in excess of 180



C, but it is improved by increasing

2228 EXTRUSION COOKING/Chemical and Nutritional Changes

the moisture content to more than 15% and by

minimizing the presence of reducing sugars.

Losses of Micronutrients

0010 There are relatively few foods which can be con-

sumed without some form of processing or cooking.

Indeed, as in the case of starch, mechanical and

thermal processing is often essential in order to

render nutrients available for absorption and utiliza-

tion by the body. On the other hand a high water

content, high temperature, and vigorous mechanical

disruption tend to cause losses of vitamins and min-

erals by leaching or chemical reaction. Thus, a bal-

ance is needed to achieve the optimal nutritional

value in a manufactured food, and this applies to

the use of extrusion technology, as much as to any

other form of industrial processing. (See Vitamins:

Overview.)

Water-Soluble Vitamins

0011 The water-soluble vitamins are a diverse group of

reactive compounds. In general, a high moisture con-

tent and temperature will favor the destruction of

such compounds during processing, but of course

these effects can be minimized by a short duration.

With its relatively low moisture content and short

residence times, extrusion cooking has some advan-

tages over other forms of processing, but these tend

to be offset if the particular application requires a

very high temperature and shear stress. This complex

situation is reflected by the diversity of results

reported for water-soluble vitamin losses after ex-

trusion.

0012 In general, thiamin is the B-group vitamin which

appears to be most vulnerable to destruction during

extrusion. On the other hand, riboflavin is retained

well and is least susceptible to processing variables. In

one set of experiments with extruded maize grits, for

example, the recovery of added thiamin was only

46% under the most mild conditions used, and fell

still further when temperature and screw speed were

increased. In contrast, riboflavin recovery was 92%

under the mild conditions and was relatively unre-

sponsive to increases in temperature. However, in-

creases in screw speed and water content did lead to

a significant reduction in riboflavin content. In stud-

ies with an extruded crispbread formulation it has

been shown that losses of thiamin and other B-

group vitamins are linearly related to energy input.

Similar considerations apply to folic acid, pyridoxin,

and niacin, although these vitamins appear to be

more stable. (See Niacin: Properties and Determin-

ation; Vitamin B

: Properties and Determination;

Riboflavin: Properties and Determination; Thiamin:

Properties and Determination.)

0013Vitamin C is susceptible to oxidation during pro-

cessing, cooking, or prolonged storage. Extrusion

cooking, like other methods of processing, leads to

losses of vitamin C from raw materials such as potato.

Supplementation can be used to overcome this prob-

lem, but retention is maximized by supplementing

after extrusion. At high operating temperatures the

stability of vitamin C during extrusion cooking is

favored by a low water content. (See Ascorbic Acid:

Properties and Determination.)

Fat-Soluble Vitamins

0014Vitamin A activity may be destroyed during extrusion

cooking, but the losses depend both upon extrusion

conditions and the nature of the carotenoids in the

commodity. Higher screw speeds have been reported

to favor increased retention of b-carotene in maize

meal. Vitamin E appears to be particularly susceptible

to severe extrusion conditions, and losses as high

as 66% have been reported for an extruded

product containing wheat germ. There is little infor-

mation available on the fate of vitamins D and K. (See

Retinol: Properties and Determination; Tocopherols:

Properties and Determination.)

Minerals

0015Unlike many other nutrients, suboptimal mineral

status occurs relatively frequently in industrialized

societies. This is particularly true for iron and

calcium, which are essential constituents of red

blood cells and bone matrix, respectively. Mineral

nutrients are susceptible to aqueous leaching and

to reduced bioavailability due to the formation of

unabsorbable organic complexes. Extrusion cook-

ing offers potential advantages over other forms of

processing because of the generally low moisture con-

tent of extruded doughs. However, it has been

reported that retention of the phytate in wheat bran,

which forms indigestible complexes with zinc, iron,

and calcium in the human small intestine, is higher

in extruded products. This is probably because the

phytase of cereals is destroyed more readily at the

high temperatures of extrusion cooking. There is

conflicting evidence as to whether this is of any

nutritional significance in humans. (See Bioavail-

ability of Nutrients; Calcium: Physiology; Iron: Physi-

ology; Phytic Acid: Nutritional Impact; Zinc:

Physiology.)

0016Investigations using techniques which model the

release of bioavailable iron in vitro suggest that extru-

sion may help to solubilize iron in maize. Further-

more, flavoring substances and preservatives added

EXTRUSION COOKING/Chemical and Nutritional Changes 2229

to extruded snack products in the final stages of

production may act as enhancers of iron absorption.

0017 Extrusion of abrasive commodities inevitably leads

to destructive wear within the die and other vulner-

able surfaces of the extruder. A measurable rise in

available iron levels from this source has been

observed in some samples of food extruded under

experimental conditions. In theory, other metallic

contaminants might enter extruded foods, but there

is no evidence that the phenomenon constitutes either

a benefit or a hazard in any commercially manufac-

tured products.

Destruction of Antinutrients and Toxins

0018 Although the most familiar role of extrusion cooking

is in the manufacture of commercial food products in

industrial societies, it also lends itself to the produc-

tion of nutritious and palatable flours from such

staple commodities of developing countries as amar-

anth and sorghum. In these applications the process

has been shown to improve protein digestibility,

probably by a combination of partial protein denatur-

ation and the destruction of protease inhibitors. Fur-

thermore, the safety of the product may be improved

by the destruction of mycotoxins. This is particularly

important in the case of peanut meal, where extrusion

cooking in the presence of ammonia has been shown

to reduce aflatoxin concentrations significantly. (See

Amaranth; Sorghum.)

0019 Microbial cells and spores are also rapidly des-

troyed at the temperatures achieved during extrusion

cooking. The efficiency of sterilization depends upon

a combination of temperature and residence time

within the extruder. For example, in studies with the

spores of the heat-resistant microorganism Bacillus

stearothermophilus FS 1518 it has been shown that,

at 165



C, destruction of spores was complete after a

residence time of 75 s, whereas at 182



C a residence

time of only 45 s was sufficient. One possible applica-

tion of the technique is in the sterilization of spices, as

an alternative to irradiation or treatment with ethyl-

ene dioxide. Black pepper has been successfully ster-

ilized by this method. The extruded product is then

reground and has been shown to be indistinguishable

from conventionally processed pepper. (See Bacillus:

Occurrence.)

The Sensory Properties of Extruded Foods

0020 From the point of view of the food manufacturer, one

of the principal advantages of extrusion cooking lies

in its ability to compress a series of manufacturing

steps into a single continuous process. The extreme

conditions of temperature, pressure, and shear which

this requires also allow the texture and shape of the

final product to be varied in ways which have been

used to create a variety of foods with novel organo-

leptic properties. However, the physical conditions

which favor the creation of expanded products with

an attractive texture also encourage the loss of

volatile compounds which make an important contri-

bution to flavor and aroma. This is also a major

concern in other applications of extrusion cooking,

such as the sterilization of spices or cocoa, but in both

these examples it has been shown that the extrusion

conditions can be manipulated so as to achieve a

practical balance of microbiological decontamination

and preserved sensory properties. (See Sensory Evalu-

ation: Sensory Characteristics of Human Foods.)

Formation and Loss of Volatile Flavorings

0021The extreme physical conditions associated with ex-

trusion cooking encourage a variety of chemical reac-

tions which can modify the sensory properties of the

final product. This creates both problems and oppor-

tunities for the food scientist. The high temperature

generated within the extruder barrel, coupled with

the ‘flashing’ of superheated water as the extrudate

emerges from the die, inevitably leads to the loss of

volatile compounds which would otherwise contrib-

ute to the flavor and aroma. For this reason many

products are subsequently flavored by enrobement

with mixtures of oil and synthetic flavorings during

the final stages of production. To overcome the cost

and other limitations of this approach, various at-

tempts have been made to stabilize flavorings added

to the feedstock before extrusion. Techniques

employed include careful selection of carrier mater-

ials, complexation with compounds such as cyclodex-

trin, or the use of multiwall microcapsules to protect

flavorings from thermal damage and volatilization.

These approaches have been successful under experi-

mental conditions, but their wide application has

been limited by the need to tailor sophisticated

thermostable flavorants to suit each particular prod-

uct and processing strategy. (See Flavor (Flavour)

Compounds: Structures and Characteristics.)

Nonvolatile Flavoring Compounds

0022Despite its adverse effects on protein quality, the

Maillard reaction is of considerable importance as a

source of aroma, flavor, and colored compounds

which contribute to the palatability of cooked and

processed foods. Through its secondary and tertiary

stages, the Maillard reaction gives rise to a large

number of products. The volatility of these com-

pounds varies, but many are known to be retained

2230 EXTRUSION COOKING/Chemical and Nutritional Changes

within the extrudate during extrusion cooking and

can contribute to the sensory quality of the final

product. The pattern of Maillard compounds which

is obtained is sensitive to the primary amino acid and

sugar substrates available, and to temperature, water

activity, pH, and residence time within the extruder.

Since all of these factors can, in theory, be varied

during the design of a product, there would appear

to be considerable scope for ‘designing’ the flavor of

the product, along with the texture and shape.

Conclusions

0023 There is no evidence that extrusion cooking poses

unique problems for the food manufacturer. All

forms of food processing alter the nutritional quality

of foods. These changes are frequently beneficial, but

deleterious effects such as changes in protein quality

or vitamin content will often occur. The balance of

positive and negative changes has to be judged in

relation to the role which the final product will play

in the diet of the consumer. For example, a reduction

in protein quality, perhaps in a cereal product which

has been subjected to extreme extrusion conditions,

will need to be taken much more seriously in an infant

food intended for use in developing countries than it

would in a snack food intended for occasional con-

sumption in the industrialized west.

See also: Ascorbic Acid: Properties and Determination;

Bacillus: Occurrence; Bioavailability of Nutrients;

Carbohydrates: Interactions with Other Food

Components; Curing; Flavor (Flavour) Compounds:

Structures and Characteristics; Phytic Acid: Nutritional

Impact; Protein: Interactions and Reactions Involved in

Food Processing; Riboflavin: Properties and

Determination; Sensory Evaluation: Sensory

Characteristics of Human Foods; Sorghum; Starch:

Structure, Properties, and Determination; Thiamin:

Properties and Determination; Tocopherols: Properties

and Determination; Vitamins: Overview; Zinc:

Physiology

Further Reading

Alonso R, Grant G, Dewey P and Marzo F (2000) Nutri-

tional assessment in vitro and in vivo of raw and ex-

truded peas (Pisum sativum L.). Journal of Agricultural

and Food Chemistry 48: 2286–2290.

Ames JM, Gur RC and Kipping GJ (2001) Effect of pH and

temperature on the formation of volatile compounds in

cysteine/reducing sugar/starch mixtures during extru-

sion cooking. Journal of Agricultural and Food Chemis-

try 49: 1885–1894.

Camire ME (1998) Chemical changes during extrusion

cooking. Recent advances. Advances in Experimental

Medicine and Biology 434: 109–121.

Camire ME, Camire A and Krumbar A (1990) Chemical

and nutritional changes in foods during extrusion. Crit-

ical Reviews in Nutrition and Food Science 29: 35–37.

Cazzaniga D, Basilico JC, Gonzalez RJ, Torres RL and de

Greef DM (2001) Mycotoxins inactivation by extrusion

cooking of corn flour. Letters in Applied Microbiology

33: 144–147.

Martin-Cabrejas MA, Jaime L, Karanja C et al. (1999)

Modifications to physicochemical and nutritional prop-

erties of hard-to-cook beans (Phaseolus vulgaris L.) by

extrusion cooking. Journal of Agricultural and Food

Chemistry 47: 1174–1182.

Mensa-Wilmot Y, Philips RD and Sefa-Dedeh S (2001)

Acceptability of extrusion cooked cereal/legume

weaning food supplements to Ghanaian mothers.

International Journal of Food Science and Nutrition

52: 83–90.

Mercier C, Linko P and Harper JM (eds) (1989) Extrusion

Cooking. St Paul, MN:American Association of Cereal

Chemists.

EXTRUSION COOKING/Chemical and Nutritional Changes 2231

FACTORY CONSTRUCTION

Contents

Environmental Considerations

Materials for Internal Surfaces

Environmental Considerations

M O Brolchain, National Standards Authority of

Ireland, Dublin, Ireland

This article is reproduced from Encyclopedia of Food Science,

General Requirements

0001 The suitability of a site and premises for the manu-

facture of safe food at an economic cost is the main

consideration when deciding on the location and

construction of a food factory. It is frequently quite

difficult to meet these requirements. A number of

factors can put the safety of food at risk. These factors

include the external environment of the factory, the

internal design and layout, the materials and finishes

used in construction, and the security of the site. Also

included is the visual impact, both externally and

internally, as this can affect the attitudes of the work-

force. To manufacture food economically, it is neces-

sary, in addition to choosing the right process and

equipment,tohavethecorrect layout and construction.

The layout of the process must be such as to minimize

labor costs, and the premises must be constructed so

that cleaning can be carried out efficiently and effect-

ively. When designing a factory layout, allowance

should be made for possible future expansion.

External Environment

0002 Food can be contaminated by airborne material,

birds, insects, and rodents. Hence, food factories

should be sited in areas free from these possible

sources of contamination.

0003 Airborne material includes dust, microorganisms,

gases, and particulate matter. Dust in factory air

usually results from unpaved roads and yards, and

handling of products containing dust in close proxim-

ity to the factory. The most common sources of air-

borne microorganisms are effluent plants, other food

processing plants, and decaying vegetation. Dis-

charges of gases and particulate matter into the at-

mosphere are usually associated with heavy industry

but can result from the domestic or industrial use of

coal. Discharges of gases can also be associated with

industries that use solvents.

0004Birds, insects, and rodents must be excluded from

food factories. They must therefore also be excluded,

in as far as is practicable, from the immediate

environment around the factory. To achieve this,

the environment around the factory should not be

attractive to birds, nor should there be favorable

locations for the harboring and breeding of insects

and rodents. Birds are attracted by trees and a supply

of food. Stagnant or slow-moving water and over-

grown vegetation provide favorable locations for

insects and rodents. (See Insect Pests: Insects and

Related Pests; Problems Caused by Insects and Mites.)

0005It can be seen from the above that there are a

number of environmental factors that can affect the

suitability of a particular location as a site for a food

factory. These requirements are in addition to the

normal requirements when choosing any factory

site. A sufficient supply of suitable water and facilities

for the disposal of effluent must also be available. (See

Effluents from Food Processing: On-Site Processing

of Waste; Disposal of Waste Water.)

Internal Environment

0006There are many factors that must be taken into ac-

count when designing the internal environment of a

food factory, if the safety of food is to be assured and

the cost of maintaining a hygienic environment is to

be minimized. The main factors are plant layout,

plant construction, surface finishes, services, and per-

sonnel facilities. These are dealt with, in detail, in the

following sections of this article. Badly designed or

incorrectly installed processing equipment can have

serious implications for food safety. Hence, care must

be exercised in choosing and installing equipment.

To obtain the ideal internal environment, the factory

should be designed around the process and the

equipment. (See Plant Design: Basic Principles;

Designing for Hygienic Operation; Process Control

and Automation.)

Plant Layout

0007 Figure 1 shows the layout of a food processing fac-

tory. The principles used in this layout apply to all

food factories. It can be seen from the figure that

there is a logical flow of raw material from intake to

final dispatch. The raw material preparation, the

processing, and the packaging are carried out in

separate areas, and there is separate storage for

raw materials and for both finished product and

packaging. It should be noted that access to the pack-

aging area is via a changing room. This is necessary

for access to areas where high-risk food is exposed.

0008 High-risk foods are foods that may be eaten cold or

eaten after warming only, and which have the poten-

tial to support the growth of food poisoning micro-

organisms.

0009 It should also be noted that the windows are on the

north side of the building. The purpose of north-facing

windows is to prevent them from being a source of

heat. The choice for the location of service equipment

is important, if the installation and operational costs

are to be optimized.

Constructional Requirements

0010As food must be processed in a hygienic environment,

the cost of maintaining this environment should be

taken into account, when designing and constructing

a food factory. The additional capital cost associated

with a well-designed factory is more than offset by the

savings on cleaning costs.

0011When designing roof structures, external valleys

should be avoided. Even partial blocking of such

valleys will lead to the presence of stagnant water,

which can be a source of food contamination. For

similar reasons, gutters must be designed so that

they can be easily cleaned. Drainpipes should be

water-trapped at the entrance to storm or other

drains. Access to roofs should be external rather

than internal, so as to avoid contaminants from roof

surfaces being brought into the premises.

0012Internal open-girder work should be avoided, and

ceilings should be smooth and impervious. Ceilings

should be accessible for cleaning, and ideally, the

surface should be coved where ceilings and walls

meet. In many food-production areas, the ceiling

must have thermal insulation. This may be necessary

either to prevent surface condensation or to reduce

the energy costs of maintaining low environmental

temperatures.

0013Walls should also be insulated, to prevent surface

condensation. They should be free from rising damp

and be protected, where appropriate, from damage

by forklift trucks, by use of a guard rail. In modern

factories, there is always a coved surface where

walls meet the floor. It is also usual for there to be a

coved surface where walls join at right angles. The

purpose of these coved surfaces is to avoid corners

and thus aid cleaning. Panels are frequently used to

construct walls, and, if used, they must be adequately

sealed. There should be no internal horizontal ledges,

such as window sills. Such ledges lead to the accumu-

lation of dust and foreign material. Where ledges are

unavoidable, they should be sloped, at a minimum

angle of 45



0014Windows must be accessible for cleaning. In food

handling areas, they should be double glazed to avoid

condensation. In such areas, transparent polyvinyl

chloride should be used instead of glass. Broken

glass is a frequent cause of food contamination.

Windows should only be used as a source of natural

light and should be north-facing. Windows should

never be used, in a production area, as a secondary

source of ventilation.

North

Plant

services

Offices and personnel

facilities

Finished product

store

Dispatch

bay

Packaging

Cooling

Processing

Preparation

Intake bay

Raw material

store

(a) (b)

Packaging

store

fig0001 Figure 1 Plan of a food factory. Reproduced from Factory Con-

struction: Environmental Considerations, Encyclopaedia of Food

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

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

2234 FACTORY CONSTRUCTION/Environmental Considerations

0015 External doors must be rodent-proof, which means

that the gaps between the door and the frame, and the

door and the floor, or riser, must not exceed 6 mm.

External personnel doors, with the exception of emer-

gency doors, should not lead directly into a produc-

tion area. All personnel doors should be fitted with a

self-closing device. Other doors, both external and

internal, which are in frequent use, should be pro-

tected by a plastic strip curtain or an efficient electric

air curtain, if they are not self-closing.

0016 When designing floors, allowance must be made

for the effect of the use of a forklift truck or the

installation of vibrating equipment. In production

areas, floors should be constructed so that they have

natural slopes to drains. The use of heavy metal grids

to cover open drainage channels should be avoided,

as they are difficult to keep clean. In high-risk pro-

duction areas, it is now being recommended that

facilities should exist to enable the floor to be flooded

with a sterilant solution.

Surface Finishes

0017 When choosing surface finishes in a food factory,

duecognisancemustbetakenofthetypeoffood

being handled and of the type of operations to be

carried out in each area of the factory. These oper-

ations usually include environmental cleaning, and

hence the use of detergents and, possibly, steam.

There are no materials, therefore, that can be rec-

ommended for use as factory finishes, in all areas of

a food factory. (See Cleaning Procedures in the Fac-

tory: Overall Approach.)

0018 For floors, there are three broad categories of

materials that may be used: concrete, tiles, and poly-

mers. Floors must be impervious, easy to clean, and

not slippery, even when wet. The suitability of a given

flooring material may, also depend on its resistance

to impact, wear and abrasion, and its inertness to

chemical or biochemical attack. Ordinary concrete

can be used in some areas, but it is subject to attack

by strong acids and alkalis. Additives, or special

aggregates such as granite chips, can be used to in-

crease surface strength and nonslip characteristics.

Ceramic or quarry tiles can be used for factory floors.

However, floor tiles are usually only as good as the

bedding, jointing, and grouting materials that are

used. When laying tiles on floors, rubber latex

cements, epoxy resins, and furane cements are often

recommended. Polymers can be used on their own, as

a surface finish or as additives to cement. Most

polymers used in food factories are derivatives of

epoxy, polyester and acrylic resins, and rubber latex.

Care must be exercised in selecting a suitable

polymer and in preparing the surface prior to laying

the polymer.

0019Walls must be impervious, smooth, and easy to

clean. To achieve this requirement, cement rendering,

paints, and polymers are used. The choice is depend-

ent on the operating environment. Failures in paints

are usually attributable to inadequate preparation of

the surface, to environmental conditions, or to unsuit-

ability of the paint. Such failures can lead to contam-

ination of food, as a result of flaking. Suitable finishes

on walls can also be obtained by using cladding or

paneling, provided that they are properly sealed.

Services

0020In modern food factories, it is usual to have all the

service lines, with the exception of drainage, located

between the ceiling and the roof. Services are then fed

vertically to the various pieces of equipment. This

design has many advantages. In particular, it makes

the maintenance of hygiene in food handling areas

more economical. In some factories, this type of

design is impractical. In such cases, the service lines

must be designed and installed so that they do not

interrupt the smooth finish on walls and ceilings.

They must also be designed so that they are accessible

for cleaning. The problem with exposed service lines

is that dust and food particles form deposits on the

top surfaces of the lines. It is usually expensive to

maintain such lines in a clean condition. When ser-

vices are being installed, it is critical that service entry

and exit points are adequately sealed, to prevent

access by rodents.

0021As mentioned earlier, windows should not be used

for ventilation in food factories. Ventilation must be

sufficient to prevent condensation on walls, ceilings,

and overhead structures. Airflows within the factory

must be designed so as to avoid product contamin-

ation. Where there are single air entry and air exit

points, airflows must be in the opposite direction to

product flows. Air-intake points must be at least 1 m

above both internal and external surfaces. They must

be fitted, at least, with a fly screen and ideally with

dust filters. It is now generally accepted that high-risk

processing areas should be kept under positive pres-

sure and that the air supply should be filtered to the

required class. Where refrigerated air is required, for

food-safety reasons, in production areas, low air

velocities are required to reduce the chill factor. To

achieve low air velocities, various refrigeration

systems may be used.

0022In most areas of food factories, floor drainage is

essential. All floor drains must be fitted with an

effective water trap and a suitable grill. The sewerage

lines must be adequate in size for effective drain-

age during washing. When designing factory

drainage, allowance must be made for equipment,

which requires a drainage outlet. Manholes should

FACTORY CONSTRUCTION/Environmental Considerations 2235

not be present internally within the factory, and, if

present, they must be doubly sealed. As food factory

sewers have to be cleaned on occasion, manholes

must be provided outside the factory to enable this

cleaning to take place.

Facilities for Personnel

0023 Adequate facilities must be provided for personnel.

Such facilities include a canteen, locker room, toilets,

and hand-washing facilities in production areas. The

provision of suitable showers is also recommended. It

is important that these facilities are well designed and

can be maintained in a hygienic condition. This is

necessary to maintain the correct hygiene ethos in

the workforce. Toilets and canteens must be venti-

lated separately and must not lead directly into a

production area. The doors leading into the lobby

and into the toilets should be fitted with a push

plate on the outside and a handle on the inside.

Ideally, the lobby outside toilets, used by production

personnel, should be of sufficient size to enable per-

sonnel using the toilets to hang up their protective

clothing, prior to entering the toilet. Hand-washing

facilities in production areas and in toilets used

by production workers must be fitted with taps that

are either knee-, foot-, or electronically operated, to

prevent recontamination of hands after washing.

Hand-drying facilities must be provided, and air

driers are not recommended in production areas, as

they could lead to the spread of aerosolized bacteria.

Paper towel or cabinet roller towels may be used in

such areas. Access to high-risk production areas

should be restricted. Entry and exit should be via a

changing room with hand-washing facilities.

Security

0024 It is now becoming the norm to control access to

food factory premises. This is usually achieved by

fencing the factory site and having a single combined

entry and exit point manned by security personnel.

In some cases, this is supplemented by the use of

television cameras and monitors for surveillance

of the premises and the perimeter fences. Frequently,

car parking is only permitted in a parking area

external to the fenced site. Car parks can be located

within the site, if under the supervision of the security

personnel.

0025 The purpose of this level of security in food factor-

ies is to reduce the level of pilferage and to prevent

entry to the site by unauthorized personnel. The latter

is of increasing importance, as a means of preventing

either inadvertent or deliberate contamination of the

company’s products. Various systems can be used for

the authorization of entry to the site of visitors, and

their identification while on site.

Esthetic Design

0026In designing food factories, the emphasis has tended

to be on functional design. The appearance of the

buildings and site from an esthetic point of view has

often been ignored. All food factories should be at-

tractive and pleasing to the eye. The importance of a

visually pleasing factory and factory site cannot be

overemphasized. Such a site helps to create a better

ethos in the workforce and better hygiene practices. It

also helps to improve the image of the company pro-

jected to customers and prospective customers.

0027In summary, there are many factors that must be

taken into account when designing a food factory if

the external and internal environments of the factory

are to be suitable for the production of safe food at an

economical cost. Ignoring any one of these factors can

result in the environment being unacceptable for food

production.

See also: Cleaning Procedures in the Factory: Overall

Approach; Effluents from Food Processing: On-Site

Processing of Waste; Disposal of Waste Water; Insect

Pests: Insects and Related Pests; Problems Caused by

Insects and Mites; Plant Design: Basic Principles;

Designing for Hygienic Operation; Process Control and

Automation