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

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CONVENIENCE FOODS

J E Tillotson, Tufts University, Medford, MA, USA

History

0001 Today, convenience foods supply much of the food

requirements of the world’s population in the indus-

trial countries. Their prominence in the modern diet is

the result of the urbanization of society during the

nineteenth and twentieth centuries. The universal

consumption of convenience foods has arisen from

the demands of modern lifestyles in the industrial

countries requiring, for the majority of people, that

their daily nourishment be supplied by commercial

enterprises rather than by their own food-producing

endeavors.

0002 Ever-growing, global urban populations, increas-

ingly without direct access, ability, desire, or time

for growing and preparing food, but with rising

financial means, have increasingly wanted the con-

venience, availability, and taste of commercially pro-

cessed foods. This market demand has motivated the

growth of a global network of food-processing and

distribution industries, supplying all manner of con-

venience foods that, by 1999, had an estimated world

retail sale value of US$4000 billion. Today, at any

given time, tens of thousands of various types of

convenience foods are offered for sale to consumers

throughout the world. All of them offer consumers

the advantages of food that is readily available, con-

venient, inexpensive, and often of surprisingly pleas-

ing organoleptic quality, requiring only minimal or no

preparation before consumption.

0003 Convenience foods can be looked at in several

ways. These foods can be narrowly classified by the

type of processing technology employed: canning,

freezing, dehydration, chilling, chemical preserving,

etc., or by the type of food: frozen and canned

vegetables; cake mixes and bakery products; soups,

sauces, and condiments; processed meats and

fish; chilled and frozen dairy-based products;

ready-to-eat and shelf-stable dishes; plus many other

types.

0004 Convenience foods can also be further interpreted

in a broader sense, beyond the specific production

technology or product type, as a vehicle of explaining

the dynamics and development of our food supply in

recent times, and as an aid in envisioning the future

nature of people’s nourishment. History teaches us

that what constitutes convenience food has changed

a number of times to meet the changing food needs of

society.

0005As it has been observed that, ‘an army travels on

its belly,’ so it is equally true that, ‘modern society

survives on convenience foods.’ Today, convenience

foods are not simply add-on, optional products, but

have now become central to supplying society’s

nourishment. How do we explain this growth of

commercialization of our food supply?

0006While the availability today of the plethora of con-

venience foods is the result of brilliant technological

innovation and scientific discovery, their current

prominence in the diets of the world’s industrialized

countries cannot be fully explained solely by the

application of food technology to the food supply.

Food technology has been more of an enabling factor

than a motivating force. Other types of technology,

including transportation and communications, have

also been significant in assisting the market growth of

convenience foods.

0007Above and beyond the diverse technical forces

involved, the phenomenon of convenience foods is

best understood in the broader context of the social,

economic, and political forces that are also respon-

sible for their wide acceptance. During the last cen-

tury, these diverse forces have shaped and motivated

the central role that convenience foods have come to

play today in the modern diet. The following inter-

prets the economic, social, technical and political

dynamics that have led to the central role of conveni-

ence foods in the modern diet. Processing technology

descriptions as well as detailed accounts of specific

types of convenience food are treated in other sections

of this encyclopedia.

Early Convenience Foods

0008In the mid-nineteenth century, a food-supply revolu-

tion began that has continued to the present. This

revolution would result in fundamental changes in

the forms of food that people in the industrial coun-

tries would depend on for their daily nourishment.

While food had been preserved as early as 4000 bc

by methods such as drying, salting, smoking, and

pickling, the nineteenth century urbanization brought

the need for a better organized, comprehensive,

and dependable system of food processing and

distribution.

0009In this era, the industrial revolution was beginning;

the new factories and the accompanying commerce

of the period required large new labor forces in

the industrial cities of Europe and America. Many

1616 CONVENIENCE FOODS

people left rural life in agriculture to work and live in

the new industrial centers. In new urban jobs, these

workers required food that was both readily available

and affordable. A new food-supply system sprang up

to meet the new urban population’s needs. This initi-

ated the trend that resulted over time in an ever-in-

creasing percentage of the population depending on

fewer and fewer others to supply their food. These

social and economic changes set in motion the indus-

trialization of the food supply, and with it, the devel-

opment of convenience foods.

0010 As the industrial era of the nineteenth century was

enabled by the application of multiple technologies,

the industrialization of the food supply was similarly

based on the simultaneous application of multiple

technologies. The movement of vast numbers to the

new large cities, removed from their own participa-

tion in agriculture, created a food-logistics problem

that the growth of new railroad systems in Europe

and North America would help to alleviate.

0011 Supplying the ever-increasing demand in the new

urban centers required transporting food from ever-

larger geographical growing areas. Because of the

economics involved in the procuring and handling

of raw agricultural commodities (e.g., wheat, cattle,

vegetables, sugar, milk), the basic processing of these

commodities became attractive in new, dedicated pro-

cessing plants in the growing and producing areas,

often located far from the growing cities. The rail-

roads were essential in transporting these processed

basic food ingredients to the cities.

0012 The urban populations were able to buy staples

(e.g., flour, white sugar, meats, and dairy products)

in the newly appearing local grocery stores. Urban

workers used their industrial wages to pay for the

basic food ingredients required in preparing their

daily meals. Their wages also paid for the conveni-

ence of letting others grow, process, transport, and

sell, as well as for the availability of these basic food

ingredients. This established the economic model that

became the foundation of convenience foods to this

day, whereby money was exchanged not only for

the basic agricultural commodity, but also for the

labor and other services associated with the food or

ingredient offered.

0013 Historically, the majority of early preserved foods

used primitive preserving methods (e.g., drying,

salting, etc.) that had been developed over centuries

of trial-and-error, and were designed solely for the

purpose of storing present food surplus of agricul-

tural products against future needs. The quality of

these primitive ‘convenience foods’ was often ques-

tionable. During the mid-1800s, the developing

new commercial food supply system produced the

first products that would conform to the modern

definition of convenience foods. With the commercial

introduction in the nineteenth century of canning –

the heat preservation of food in glass or metal con-

tainers – convenience foods assumed new identities,

quality and importance. Consumers of this era would

become ready buyers of these first mass-produced

convenience foods.

0014In England, Brian Dookin established one of the

first industrial canning factories. By 1812, he had

started his canning factory and 6 years later was

producing cured beef, boiled beef, carrots, mutton-

and-vegetable stew, and soups of various types in

tinned iron containers. However, due to their high

cost, only travelers, explorers, and the military used

these initial canned foods.

0015By 1868, the earlier handmade cans were replaced

by machine-cut, assembly-line-produced containers,

with a concomitant reduction in production cost and

improved quality. In the late 1870s, new methods of

processing under steam pressure reduced processing

times and made large-scale production possible. By

1910, a single can-making machine could produce

up to 35 000 containers a day. These technological

advancements, combined with the use of integrated

food-handling equipment to peel, shell, clean, slice,

chop, and cook various foods, made canned products

inexpensive to produce and, as a result, affordable

and acceptable as convenience foods by millions of

people. The production model developed at this time

that yielded low unit costs and reliable quality would

be the basis of the manufacturing strategy for

convenience foods in the future.

0016In 1910, American processors, employing more

than 68 000 factory workers, were producing over 3

billion cans of food. The large capital investments

necessary for a modern cannery of the period favored

the formation of large processing companies, many of

American origin (e.g., Heinz, Campbell’s). The large-

scale production of these new convenience foods

required large and expanded markets for their sale.

Aided by the transportation and communication revo-

lution occurring at this time, the United States market

was developing from regional to national scope,

which, fueled by the country’s economic growth and

rising incomes, offered the necessary commercial

outlets for fast-increasing, canned-food production.

0017Food processors at this time came to realize that

their future market success depended on more than

technological, logistical, and manufacturing abilities.

In order to build competitive and sustainable distri-

bution, businesses would require an understanding of

the factors influencing the demand side of their busi-

nesses. They realized that attracting and retaining

consumers were critical to their future commercial

success.

CONVENIENCE FOODS 1617

0018 Beginning in the 1860s, progressive processors

started to commit the time, energy, and resources

necessary to acquire a better understanding of the

consumers’ needs. Leading food canners used this

information to craft attractive national reputations

for their companies and their products. Their

marketing response was to build consumer-recog-

nized and trusted brands through effective packaging,

advertising and promotion. After the 1880s, rapidly

growing food companies began branding their prod-

ucts for national distribution. As the scope, scale, and

reputation of their nationally distributed brands

expanded, shoppers now, unlike in the past where

they depended on a local retailer for buying advice,

came to know, trust, and purchase national brands for

the quality they embodied. This brand marketing in-

novation would become the future business model for

the success of convenience foods to this day.

0019 Initial development of convenience foods during

this period was not limited to canned foods. Other

types of convenience foods produced with different

technologies and packaged in other types of contain-

ers became nationally available during this period

through then-proliferating neighborhood stores,

beginning to organize into grocery chains. Most

famous and enduring among these were convenience

entries in the (then) new category of breakfast cereals.

Early leaders in packaged cereals were Kellogg’s

‘Corn Flakes’ and Post’s ‘Grape-Nuts,’ which became

most successful in encouraging Americans to sub-

stitute these products for their former breakfast

choices.

0020 By the 1880s, several rapidly growing companies

were packaging and branding a wide range of other

food products – Procter & Gamble, Pillsbury,

Nabisco, Borden’s – that are still prominent brands.

The immediate and sustained market success of these

new-to-consumers forms of convenience foods pre-

dicted the major role that these foods and their

promotion would play in shaping the future diets

in the industrial countries. The consumer attraction

and durability of these leading brands also presaged

the importance of product innovation, advertising

and promotion, and wide distribution to which

the market success of convenience foods owed so

much.

0021 In addition to the technological, social, and eco-

nomic factors responsible for the early successful

development of convenience foods, political factors

also would be significant. Increasingly during the

nineteenth century, the safety and quality of various

processed foodstuffs were a growing concern with

the public, and not without justification. Progressive

canners, such as Henry J. Heinz and others, came to

realize that because of the sharp practices of some

processors, consumers were often suspicious of

processed foods: this concern had the potential to

adversely affect the industry’s future. Government-

imposed standards were necessary to prevent mis-

labeling and food adulteration, occurring all too

often in this era.

0022During the period of the 1880s up to the successful

passage of the US Pure Food and Drug Act in 1906,

various state and federal legislators, government and

academic food experts, civic and professional organ-

izations (American Medical Association, National

Consumers’ League, General Federation of Women’s

clubs), and a number of food processors lobbied for

government oversight. The passage of this Act and the

resulting government agency oversight of the industry

gave the public the necessary faith in processed foods

to further enhance their wide acceptance. Earlier

similar food laws had been passed and implemented

in other industrial countries with parallel results. The

first British Food and Drugs Act was passed in 1860

and then extensively revised and strengthened in

1872.

Packaged and Branded Convenience

Foods

0023In the period between the last quarter of the nine-

teenth and the first quarter of the twentieth century,

commercially produced convenience foods became

established in the diets of the industrial countries.

The nascent food-processing industries of that era,

producing these early convenience foods, were still

learning the skills of economically mass-producing

products. Of equal importance, the companies were

learning how to brand, distribute and effectively

market these early convenience foods on a more

national scale.

0024Consumers not only accepted, but also had an

apparent great desire and need for, more and more

of these convenient products that fitted their new

urban lifestyles so well. The food-processing indus-

tries responded aggressively to this growing consumer

demand during the early part of the century. The

social, technical, economic, and political foundations

had been established for the next phase – the 1930s

through 1980s – for the rapid growth and prolifer-

ation as well as improvement of convenience foods

with their ‘built-in-chef service.’ These second-

generation packaged foods would be an integral

part of this new era with its lifestyle that would

become known as ‘the golden age of consumer

products.’

0025New advances in convenience foods would depend

on a greater scientific understanding of food process-

ing and handling. While canning had been practiced

1618 CONVENIENCE FOODS

since the eighteenth century, it was not until the end

of the nineteenth century that canning was estab-

lished on a firm scientific basis by research at the

Massachusetts Institute of Technology. While urban

populations were becoming accustomed to early

mass-processed convenience foods, the scientific

foundation for the myriad advanced convenience

foods, which would be introduced in the 1930s and

later, was being established in the research laborator-

ies of government institutes, universities and food

companies.

0026 A notable achievement of this new science-based

food innovation era was the first market intro-

duction in the 1920s of packaged frozen foods by a

company founded by Clarence Birdseye, generally

considered to be the initial patent-holder and first

commercial developer of frozen foods. Frozen foods

offered stored processed foods with a markedly

improved texture, color, and taste over equivalent

canned foods. The availability of frozen foods, with

their improved eating quality versus canned foods

presaged a trend that would continue during the nine-

teenth century: a newly developed processing technol-

ogy, yielding an improved convenience food, would

replace products manufactured with an older technol-

ogy. Consumer markets would respond favorably to

the ‘new and improved’ marketing claims of these

new consumer products.

0027 The first part of the twentieth century would prove

to be a very productive era for food science and

technology. Notable commercial convenience-food

successes resulting from new knowledge would be:

Crisco, hydrogenated vegetable shortening by Procter

& Gamble in 1911; strained baby food in individual

glass jars by Gerber in 1927; Wonder Bread, pack-

aged, sliced white bread in 1930 by Continental

Baking; frozen June peas and frozen spinach by

Birds Eye in 1930; Ritz Crackers by National Biscuit

Co.(Nabisco) in 1933, which, in 3 years, would

become the world’s largest selling crackers; soluble

(instant) coffee, first produced by Nestle

in 1938 as

the Nescafe

brand, using countercurrent roast-coffee

water extraction, followed by spray drying, and later

improved by General Foods in 1964 by a freeze-

drying technology, marketed as Maxim freeze-dried

instant coffee; Minute Maid, frozen orange juice

concentrate by the Minute Maid Corp. in 1947; pack-

aged, prepared cake-mixes by General Mills and Pills-

bury in 1948; Frozen TV dinners by C.A. Swanson’s

& Sons in 1953, using flash-freezing technology; and

many other famous, convenience foods consumed to

this day.

0028 Through the period of the 1950s to the 1980s,

there seemed to be no end to the growth of these

new branded, packaged foods. This was especially

true for the leading brands in the various supermarket

categories. The consumer food industry, with the

help of sophisticated input suppliers – packaging

companies, process equipment manufacturers, and

numerous suppliers of food ingredients, flavorings,

and food additives – formed industrial clusters

that served as sources of product innovation. This

resulted in ‘new products’ introductions entering

American supermarkets in the thousands of items

per year. New methods of consumer research vastly

improved the commerical development process by

identifying potential consumer needs and desires

prior to the actual physical development efforts.

Nevertheless, new product failure rates were always

high, but the great profitability of successful market

winners justified the cost of both continuous prod-

uct development efforts and the high advertising

and promotion expenses of introducing new

products.

0029These second-generation convenience foods were a

perfect fit for the era, and they captured the contem-

porary consumer tastes and lifestyles. Consumers –

having survived the Great Depression of the 1930s

and the Second World War – were eager for the

benefits of the new consumer society that followed,

providing new products often previously unavail-

able. These new, and improved, consumer products

fitted their rising incomes and new social aspirations.

New home appliances, such as refrigerators with

frozen food compartments and microwave ovens, as

well as second family cars and new television sets

were all necessary stimuli to the growth of the new

branded, packaged convenience foods. The large

volumes of these new mass-marketed foods – required

for supporting their relative low cost – spurred the

transformation of food retailing, giving rise to new

large, shopper-friendly, self-serve supermarkets

offering and selling thousands of new, attractive

food items.

0030Housewives, often living in new suburban

surroundings, driving second family cars and now

having the time, desire, income, and shopping interest

became avid purchasers of the new convenience

foods. The increasing prevalence of then-new TVs in

their homes gave marketers of convenience foods an

economically effective means of introducing and

marketing their products. As a result, the packaged

convenience food industry experienced an unparal-

leled era of great prosperity. While there were safety

questions raised concerning the increasing use of food

additives, chemicals and new packaging in conveni-

ence foods, new laws addressed the majority of these

safety concerns but did not restrict their increasing

use in food manufacturing as well as the market

growth of new convenience foods.

CONVENIENCE FOODS 1619

Ready-prepared Convenience Foods

0031 In the middle of the golden era of consumer products,

while mass-marketed, supermarket-sold, branded,

packaged convenience foods were setting new con-

sumption records, a new type of convenience food

was rushing into the market place: ready-prepared

foods that offered consumers the ultimate in utility

and convenience, food requiring no preparation,

complete and ready for consumption. Foods, both as

hand-held snacks or full meals that can be purchased

in fast-food outlets and restaurants, as well as in

supermarkets and stores of all other kinds, and

eaten at the site of purchase, in the home, or on the

move. While the convenience of ready-prepared food

has, in a sense, been available in many forms since the

time of the Roman Empire and their cookshops, the

rapid and extensive growth plus the commercial

origin of these modern ready-prepared foods was

without parallel.

0032 By the 1990s, this new wave of convenience ready-

prepared foods would largely blunt the phenomenal

growth experienced by packaged, branded conveni-

ence foods in the US supermarkets since the 1940s. By

the early 1990s, total consumer retail spending on

foods of all types at all sales outlets had reached

approximately US$700 billion annually equally

divided by shoppers between traditional processed

foods and new ready-to-eat foods. These new con-

venience foods became available everywhere: in res-

taurants of all types, catering, and institutional outlets

(schools, universities, hospitals, government, and

industrial cafeterias). Even supermarkets and stores

of many kinds joined the new trend to offer also take-

out, ready-prepared foods. By late 1990s, applying

the successful marketing and branding techniques

developed earlier by the packaged food industry,

the annual growth of ready-prepared foods was out-

distancing traditional foods sales by approximately

four-to-one (4% versus 1–2%) annually. In other

industrial countries, a similar trend was occurring,

but not yet to the same extent as in North America.

0033 The ever-changing concept of convenience foods

was taking on still another identity, driven by a new

set of social, economic, and technical factors. Socio-

economic factors, in particular, were largely respon-

sible for the success of these new ready-prepared

convenience foods. Americans were experiencing

unprecedented economic growth, affluence was

molding their expectations, and ready-prepared

foods became ‘affordable luxuries’ for all. A major

factor in the changing economy was increasing par-

ticipation by women in the work force; the number of

women working outside the home doubled from fewer

than one in three in the 1950s to nearly two in three in

the 1990s. Overworked, time-constrained consumers,

often in dual-income or single-parent households, not

having the time, energy, or desire to cook, moved from

the traditional never-changing meal schedules of the

past to unstructured and fast-paced feeding schedules.

Furthering this trend was the number of married

households with children in the USA, which declined

from 40% in 1970 to 24% in 2000.

0034Ready-prepared convenience foods were ideally

suited, in both form and price, to the new eating

patterns. Americans, both young and older, experi-

encing new lifestyles, increasingly prefer the easy

availability, immediate service, and fresher taste of

ready-prepared foods, as opposed to highly processed,

packaged foods requiring supermarket purchase,

tiring transfer to the home, and then preparation

and clean-up. Food also became more than just

daily nourishment, but often entertainment, too, as

people were experiencing new tastes, foods of new

ethnic varieties, and new types of restaurants. By the

1990s, Americans appeared to be eating convenience

foods continuously and everywhere; concurrently,

their away-from-home eating places were changing,

as well as the types of food they were eating.

0035Between 1970 and 1990, the number of full-service

restaurants per 100 000 people fell by one-quarter,

and the number of bars and luncheonettes by half.

New eating spots – fast-food outlets – were taking

their place; during the same period, the number of

fast-food outlets doubled. The majority of these were

part of huge national and even international chains

that been started in the 1950s and 1960s (McDon-

ald’s, Burger King, Kentucky Fried Chicken, now

known as KFC). These fast-food chains, with their

hamburgers, French fries, fried chicken, and soft

drinks, combined with new moderate-priced, family-

style restaurants (Denny’s, Red Lobster), pizza shops

(Domino’s, Pizza Hut), and coffee outlets (Dunkin’

Donuts, Starbucks) and assorted other types, would

come to dominate America’s new convenience food

industry, with an estimated 40 million people per day

eating at, or meals from, fast-food outlets in the 1990s.

By 1998, the 20 largest fast-food chains would have

79 922 outlets, with annual sales of US$56 billion,

accounting for 23% of total US restaurant sales,

often located side-by-side, convenient by automobile,

in or by major shopping malls and highways.

0036In order to compete, supermarkets would start to

offer ready-prepared items, as did many other types

of food shops. Traditional food companies also

started to offer chilled, ready-prepared convenience

foods. The same economic and social trends that

favored the growth of the fast-food outlets also

favored an equally strong growth of all types of insti-

tutional foodservice. These new convenience foods

1620 CONVENIENCE FOODS

with the often pervasive use of their brand names,

have led to brand-name, fast-food outlets now preva-

lent in food courts of shopping malls and as mini-

units in corporate, institutional, and governmental

food settings.

0037 As the nature of convenience foods has changed,

so have the technologies to deliver the new ready-

prepared consumer items. The traditional food indus-

try practices the technologies of product formulation,

processing, and packaging designed for product

stability, often at ambient temperatures or deep-

frozen, and months-long storage times, plus potential

distribution over long distances. Ready-prepared con-

venience food technology has other objectives: fresh-

ness, short shelf-life, and capability of being prepared

on demand for waiting customers in minimum time,

by nonskilled labor. Often the fast-food outlet is

merely the final stage in a vast, highly complex system

of mass production that gathers the necessary agricul-

tural products and ingredients, partially prepares and

processes them – often in central commissaries – for

final and speedy, minimal preparation at consumer

store level. This new segment of the food industry

has industrialized the final preparation of food that

occurred in the past in the home kitchen.

0038 The nature of ready-prepared food production,

often with short-shelf-life products, requires organ-

izations with great skill handling timely logistics and

exacting, day-to-day market-demand forecasting. As

a result of the significant differences in the necessary

business skills required for ready-prepared foods as

compared with traditional processed foods, the

leading marketers of these new convenience foods

are predominantly business organizations quite

different from the traditional food processors.

0039 While the major fast-food chains have acquired

such market dominance and apparent invincibility

in supplying modern consumers’ diet at the start of

the twenty-first century, political forces are building

that could prove to be problems for their further

growth. Concern about the narrow dietary com-

position and high fat content of fast-food menus is

growing, and questions are being raised by medical

professionals and government health policymakers,

especially given their high rate of consumption by

the young.

Summary

0040 Over the last 150 years, populations of the industrial

countries, as well as those of the recently developing

countries, increasingly favor convenience foods as

diet mainstays. Convenience foods cleverly meet the

nourishment needs of modern life. World-wide shop-

pers want the advantages these foods offer: taste,

quality, variety, economy, availability, nutrition,

safety, and – above all – their labor-saving functions.

Today, these foods offer the advantage of minimum,

or even nil, preparation effort, and they are available

everywhere at attractive prices. Their consumer

prices are being determined more by the ‘added-

value’ services offered than by the cost of ingredients

used in their production. Convenience foods have

changed the diet for many, while enhancing our

modern, quick-paced lifestyle. They again confirm

that ‘food is never just something to eat.’ (From

Much Depends on Dinner, by Margaret Visser, 1986).

0041New food science and technology, combined with

associated packaging and processing technologies as

well as advances in communication, distribution, and

marketing, have enabled the development of a series

of convenience foods and added to ever-increasing

consumer satisfaction. However, basic to their phe-

nomenal growth are the changing social, economic,

and political factors responsible for their wide every-

day consumption. As the nature of these environmen-

tal factors has changed over the past century, so has

the basic identity of convenience foods. As we have

seen in the three major past transformations of con-

venience foods – early, brand and packaged, and now

ready-prepared forms – outlined above, so it is likely

that the nature of convenience foods will change

again in reaction to new social, technical, economic,

and political forces.

See also: Canning: Principles; Quality Changes During

Canning; Cereals: Breakfast Cereals; Freezing:

Principles; Packaging: Packaging of Solids

Further Reading

Baas E, van Battum S, Voor bergen M and Zwanenberg A

(1999a) The World Food Markets. Utrecht: Rabobank

International.

Baas E, van Battum S, Voor bergen M and Zwanenberg A

(1999b) The Fight for Stomach Share. Utrecht: Rabo-

bank International.

Beardsaworth A and Keil T (1997) Sociology on the Menu.

New York: Routledge.

Bowley R (2001) Carried Away: The Invention of Modern

Shopping. New York: Columbia University Press.

Emerson R (1979) Fast Food: The Endless Shakeout. New

York: Lebhar-Friedman.

Hughes D (ed.) (1994) Building with Tradition. Wye, UK,

Wye College Press.

Kahn B and McAlister L (1997) Grocery Revolution: the

New Focus on the Consumer. Reading, MA: Addison-

Wesley.

Koehn N (2001) Brand New. Boston, MA: Harvard

Business School Press.

Levenstein H (1988) Revolution At The Table. New York:

Oxford University Press.

CONVENIENCE FOODS 1621

OECD (1998) The Future of Food. Paris: Organisation for

Economic Co-operation and Development.

Pillsbury R (1998) No Foreign Food: The American Diet in

Time and Place. Boulder, CO: Westview Press.

Putnam R (2000) Bowling Alone: The Collapse and Revival

of the American Community, New York, Simon &

Schuster.

Schlosser E (2001) Fast Food Nation. New York: Houghton

Mifflin Company.

Senauer B, Asp E and Kinsey J (1991) Food Trends and the

Changing Consumer. St. Paul, MN: Egan Press.

Tannahill R (1988) Food in History. New York: Three

Rivers Press.

Tillotson J (2000) Global supermarkets. Nutrition Today 35.

Cookies See Biscuits, Cookies, and Crackers: Nature of the Products; Methods of Manufacture; Chemistry

of Biscuit Making; Wafers

COOKING

Contents

Domestic Techniques

Domestic Use of Microwave Ovens

Domestic Techniques

A J Rosenthal, Oxford Brookes University,

Headington, Oxford, UK

Introduction

0001 As with all forms of cooking, domestic cooking is

intended to improve the palatability of the food,

making it more appetizing. Unlike industrial food

preparation and catering or food service, domestic

cooking is carried out in the end user’s home, by

people who may not have any technical knowledge

of what is happening from an engineering or bio-

chemical point of view. By definition, cooking raises

the temperature of the food. This results in a number

of simultaneous and interrelated processes which in-

fluence the flavor, texture, appearance, nutrient con-

tent, and safety of the food. The different techniques

of domestic cooking reflect the way in which the

temperature of the food is raised (Figure 1).

0002 Clearly, there are two basic ways in which energy

can be applied to a foodstuff, resulting in a rise in

temperature. The traditional route is by contact with

a heated medium which causes heat to flow to the

surface of the food and then on to the center by

conduction. An alternative route is to apply electro-

magnetic radiation. Of the two types of electromag-

netic radiation commonly used in domestic cooking,

infrared, radiant heating (grilling) employs short-

wavelength radiation which is only able to penetrate

a couple of millimetres below the surface of the food.

The inner regions of the food heat by conduction.

Microwaves have longer wavelengths which are able

to penetrate deep into foods, generating heat in situ.

0003In many cases energy transfer during cooking is not

by a single mechanism. For example, ovens absorb

and emit infrared energy and baked food heat by a

combination of convection and radiation. Similarly,

barbecues emit infrared radiation as well as generat-

ing hot combustion gases, which flow around the

food, heating it by convection.

General Considerations

Surface Heat Transfer

0004The crucial difference between the different tech-

niques of heating by contact with a heated material

is what happens at the surface of the food.

0005When a solid food is placed in a hot fluid, there is a

stagnant layer of fluid around the food. This bound-

ary layer acts as an insulating barrier which slows the

flow of heat from the fluid to the food.

0006Air is a good insulator (thermal conductivity,

0.024 W m

1

); therefore a boundary layer con-

sisting of air greatly slows the flow of heat from an

oven to the food (Figure 2a). One way of reducing the

thickness of this boundary layer is to agitate the

heating medium. In the case of fan-assisted ovens,

the air is forced to circulate, thereby impinging on the

1622 COOKING/Domestic Techniques

surface of the food and physically reducing the thick-

ness of the boundary layer (Figure 2d). The surface

heat transfer coefficient in a fan-assisted oven is about

10 times greater than in a conventional oven.

0007Heat travels by conduction through static boundary

layers. Heating media which are better conductors of

heat than air will increase the rate of heat flow to the

surface of the food. Water has a thermal conductivity

of 0.573 W m

1

, and the rates of convective heat

transfer during boiling and simmering are therefore

considerably faster than in ovens at the same tempera-

ture (Figure 2e). However, the maximum temperature

attainable with water is limited by its boiling point.

Alternative liquid heating media, such as oil, have

thermal conductivities in the same region and can

operate at temperatures around 180



C. Hence rates

of heat flow to the surface in frying are considerably

greater than in boiling. This is also partly attributable

to physical agitation of the boundary layer caused by

the generation of water vapor at the surface of the food

in contact with the hot oil (Figure 2g).

0008When saturated steam is used as the heating

medium, heat flow to the surface of the food is ac-

companied by simultaneous condensing of the steam.

The dramatic volume change during condensation

results in fresh steam flowing to occupy the void,

thereby maintaining a virtually negligible boundary

layer (Figure 2). However, if the steam is not satur-

ated, then the noncondensing air accumulates at the

surface of the food, forming an insulating layer. In

fact, as little as 6% air in steam reduces the surface

heat transfer by 90%.

Energy transferred by contact with a heated:

Energy transferred by

Solid

Liquid

Gas or vapor

Typical wavelength

Oil

Water

Steam

Air convection 0.03 mm 300 mm

Atmospheric

Pressure

Natural

Forced

Griddling

Frying

Boiling

Simmering

Steaming

Pressure

cooking

Roasting/baking

Grilling

Microwave

Heat generated

throughout

All these techniques achieve surface heating:

heat flow to center by conduction

electromagnetic radiation

fig0001 Figure 1 Classification of domestic cooking techniques.

Key

Boundary

layer

(a) (b)

(c)

Oil layer

(d)

(e) (f)

(g)

Vapor

bubbles

(h)

Potato

Conduction

through

potato

Conduction through

boundary layer

Electromagnetic

radiation

Convection

fig0002 Figure 2 Eight ways to cook a potato: (a) bake; (b) bake with a

good conductor (e.g. knife) inserted; (c) roast; (d) forced convec-

tion (fan-assisted oven); (e) boil; (f) steam or pressure-cook;

(g) fry (chipped); (h) microwave.

COOKING/Domestic Techniques 1623

Rate of Heating

0009 During heating the rate at which heat flows into any

food depends on the shape and size of the food, the

temperature difference between the food and the

heating medium, as well as the rate of heat transfer

between the food and the heating medium.

0010 Shape and size influence the rate of heating. Large

surface areas obviously allow more heat to flow than

small surfaces. Shapes with more surface-to-bulk

ratio such as spherical foods will heat quicker than

other shapes such as slabs. Consequently, if we con-

sider how fast it takes heat to penetrate to the center

of two ‘spherical’ potatoes of different size we see that

it takes longer for heat to penetrate to the centre of a

large potato compared with a small one. There are

two reasons for this: the large potato has a greater

distance for the heat to flow to reach the centre and

the ratio of the heating surface area to mass is smaller

for a large potato.

0011 The driving force in any heating operation is the

difference in temperature between the food and the

heating medium. The greater the difference, the higher

therateofheattransfer.Inthecaseof domesticcooking,

foods heat by what is referred to as unsteady-state heat

transfer. That is to say that the temperature difference

reduces as the temperature of the food rises and hence

the driving force lessens as the process ensues.

0012 The physical properties of the food and the heating

system contribute to the heating rate. Factors such as

how easily the heat is able to flow through the insu-

lating surface boundary layer and then on through the

bulk of the food by conduction towards the center are

influential.

0013 Engineers who study heating processes have

methods of predicting rates of heating based on the

physical properties of materials and heating systems.

In order to illustrate the factors which influence the

rate of heating, Figure 3 has been produced. As a

measure of the heating rate, the time taken for a food

of fixed shape and size to reach a particular tempera-

ture has been used. In this figure, 2-cm-diameter spher-

ical potatoes starting at 5



C have been used. The

identical potatoes are placed into different heating

media at designated temperatures and the time taken

for the centre temperature to reach 80



C has been

predicted. The temperature of 80



C has been chosen

as a realistic center cooking temperature for many

meats and vegetables, and one which will certainly

achieve gelatinization of starch in a food like a potato.

0014Clearly, short cooking times can be achieved in a

number of ways. Working at higher temperature

achieves more rapid cooking, as does selecting a

cooking process with a high surface heat transfer

coefficient. Hence, working with a fan-assisted oven

is faster at cooking than conventional ovens because

they reduce the thickness of the insulating surface

boundary layer around the food.

Cooking by Electromagnetic Radiation

Infrared

0015As with the other traditional forms of cooking, grilling

(broiling) causes the surface of the food to heat, and

the center then heats by conduction. Absorption of

infrared radiation at the surface is proportional to

the difference of the fourth power of the temperature

of the radiation source and the surface of the food.

However, various foods absorb infrared radiation to

differing extents depending on their absorptivity (e.g.,

black body, 1; perfect reflector, 0; water, 0.96).

0016Conventional grilling and barbecuing are restricted

by the fact that radiant energy is supplied from one

direction; cooking of all sides is only achieved by

frequently turning the food, e.g., on a spit.

0017In practice, infrared heating is involved in many

cooking techniques, such as baking and roasting. In

these cases the oven walls heat up by convective heat

transfer and then emit infrared radiation.

Microwaves

0018Microwaves penetrate deep into most foods; their

sinusoidal electromagnetic waveform causes dipoles

(e.g., water) to oscillate, which in turn causes heat

(Figure 2h). As microwaves pass through a food ma-

terial their energy is lost; although heating does occur

within the food, it is greatest at the surface. The

actual temperature achieved within the food depends

on several factors, including the frequency of the

radiation, the strength of the field, the dielectric loss

factor of the food, the free moisture present, and the

shape of the food.

100

150

200

250

Temperature (˚C)

Conventional oven

Boiling water

Condensing steam

Fan-assisted oven

Time (min)

fig0003 Figure 3 Predicted time for the center of 2-cm-diameter

potatoes to reach 80



1624 COOKING/Domestic Techniques

Quality Changes during Cooking

General Considerations

0019 Mrs Beeton tells us that there are only two basic

cooking methods: wet and dry. Wet cooking includes

boiling, simmering, steaming, pressure cooking,

stewing, and poaching. During wet cooking the sur-

face temperature of the food does not exceed the

boiling point of water (usually 100



C, but up to

about 120



C in domestic pressure cookers); conse-

quently, the surface remains moist. Dry cooking in-

cludes frying (deep and shallow), baking, roasting (in

an oven with natural or added fat), grilling (broiling),

barbecuing, and griddling. The surface temperature

during dry cooking may well exceed 100



C, leading

to evaporation of moisture and a dry or crisp surface.

0020 Whatever is being cooked, it is worth bearing in

mind that most foods are biological in origin and

many are still respiring up to the time of cooking.

The rise in temperature during cooking can result in

a severe disruption of structural integrity and the

termination of normal metabolic activity.

0021 We eat a diverse range of foods, each with its own

criteria of quality. Since the changes that occur during

cooking are dependent on both the temperature

achieved in the product and the time at which the

food is held at each temperature, the quality of the

product is constantly changing. Most of the quality

changes that take place during domestic cooking can

be described by first-order Arrhenius kinetics (i.e.,

after a finite activation energy is reached, the rate of

change is proportional to a rate constant, which is

itself exponentially affected by temperature). The ac-

tivation energy and rate constant vary for different

quality factors; moreover, any particular factor may

behave differently in each food (e.g., thiamin is des-

troyed more rapidly during cooking of rainbow trout

than in a buffered solution with the same tempera-

ture–time profile). This means that if a food is cooked

on the basis of one quality characteristic (e.g., color in

meat, or texture in cakes) and if the time–temperature

treatment is varied from an established procedure,

then the other quality parameters may be suboptimal.

For example, microwaved meat may not develop the

same flavor as conventionally roasted meats.

Textural Changes

0022 No single mechanism is responsible for the texture

of foods, yet changes in protein structure and

solubilization of polysaccharides (and some proteins)

are the two primary phenomena involved.

0023 Heat causes proteins to unwind their tertiary struc-

ture. Heating for long periods or high temperatures

frequently results in irreversible changes in tertiary

structure, termed denaturation, which causes changes

in functional properties. If the protein is highly

charged, the uncoiled amino acid chains tend to

repel each other and the protein increases its affinity

for water, leading to an enhanced solubility. (See

Protein: Interactions and Reactions Involved in Food

Processing; Functional Properties.)

0024If the protein molecules are reasonably close to

their isoelectric point, the amino acid chains tend to

attract each other with hydrophobic interactions and

hydrogen bonds, forming a network of chains. This

association of molecules results in a reduction in the

amount of water which is associated with protein,

and hence the following consequences: a loss of pro-

tein solubility; precipitation of the protein from solu-

tion, giving rise to a solid structure (such a change is

responsible for the thermal setting or gelation); loss of

water-holding capacity accompanied by an aqueous

exudate from the product (often observed when

cooking meats); shrinkage of the product as both the

above occur; and increase in the opacity of the food

(e.g., egg white).

0025Some proteins undergo reversible thermal transi-

tions when heated. For example, collagen (and its

partially hydrolyzed derivative, gelatin) is solubilized

when heated. Owing to its prevalence in connective

tissue, this has important implications in tenderness

of cooked meat and is partly responsible for the

softening action of long-duration stewing.

0026Solubilization is also a process which affects poly-

saccharide material between the cell walls of plants.

Dissolution of these pectins results in softening of

the plant tissues. Addition of sodium bicarbonate

enhances solubilization of pectin by producing the

sodium salt and displacing the calcium ions which

are naturally chelated in the structure. (See Carbohy-

drates: Interactions with Other Food Components.)

0027Another mechanism commonly involved in provid-

ing rigidity in plant tissues is turgor. Denaturation

of the proteins present in the cell membranes causes

a termination of osmoregulation and a subsequent

softening of the tissues. Deliberate protein denatur-

ation is the aim of blanching, a brief exposure to

temperatures around 85



C, with the intention of

destroying flavor-modifying enzymes prior to home

freezing.

0028Starch is present in many plant foods. Heating

starch with an ample supply of water leads to

gelatinization. The granules swell as they absorb

water and the crystalline regions are disrupted. This

has both a softening and a thickening effect, which is

why gelatinized starch provides the viscosity of many

sauces. (See Starch: Structure, Properties, and Deter-

mination.)

COOKING/Domestic Techniques 1625