8/6/2019 Fact Sheet SMkt Grg

1/10

Fact Sheet

CSIRO is helping provide healthier, high quality foods to match consumer and industry

preferences.

The shelf life of foods

Shelf life is an important property of any food and is of interest to everyone in the food

chain from producer to consumer.

. Background

. Factors influencing shelf life

. Food-packaging interaction

. Challenge studies

. Domestic storageBackgroundPage 1 of 5

The legal requirement for manufacturers of packaged foods to open date mark foods wasintroduced in Australia in 1978.

This followed similar moves internationally and the publication of a standard by the Codex

Committee on Food Labelling.

It was argued by consumer groups that with the rapid changes occurring in food manufacturing,packaging and retailing that consumers could no longer rely on traditional wisdom and habits to

dictate how long a food may be stored.

Changes to the requirements for date marking of food have occurred since 1978. The current

Standard 1.2.5, Date Marking of Packaged Food of the Food Standards Code (FSC) reads in part:'the Standard requires packaged food, with some exceptions, to be date marked, and prohibits the

sale of packaged food after the expiration of the use-by date, where such a date mark is required'.

The responsibility of determining the shelf life of a food, and thus its best-before or use-by date,lies with the manufacturer/packer.

A use-by date means 'the date which signifies the end of the estimated period, if stored in

8/6/2019 Fact Sheet SMkt Grg

2/10

accordance with any stated storage conditions, after which the intact package of food should notbe consumed because of health and safety reasons'. It is an offence to sell packaged food past its

use-by date and this form of date marking is tied to food safety.

The best-before date is the open date which most packaged foods carry and is defined in the FSC

as 'the date which signifies the end of the period during which the intact package of food ifstored in accordance with any stated storage conditions, will remain fully marketable and willretain any specific qualities for which express or implied claims have been made'.

An exemption from the open date marking still applies if the best-before date of the food is two

years or more. However many manufacturers whose products fall into this category elect to datemark these foods.

Whose responsibility?

The responsibility of determining the shelf life of a food, and thus its best-before or use-by date,

lies with the manufacturer/packer.

The most direct way of doing this is to conduct properly constructed storage trials under realistic,

defined conditions.

This may not be possible for smaller manufacturers, in particular those just entering the market.

They frequently are looking for some rapid method to measure and estimate shelf life to allowthem to put their product on the market as quickly as possible.

Established manufacturers also are reluctant to rely solely on conventional storage trials to

determine shelf life.

Commercial pressures usually mean that a product must be marketed as quickly as possible afterits development. Retailers may also have their own demands about shelf life of particular product

categories especially those with a relatively short shelf life.

Indirect methods of shelf life determination are frequently used to yield results which otherwise

would be time consuming to obtain.

These may involve so-called accelerated shelf life tests usually based on storage of the product athigher than normal temperatures or computer-based models.

While these methods may prove useful, they must be applied with care.

Storage of foods at higher than normal temperatures can induce changes in the food which wouldnot occur at normal ambient temperatures. Also the rate at which normal changes are accelerated

by higher temperatures must be known with acceptable accuracy.

Models are useful only if they have been shown to mimic spoilage rates in like foods and notmerely been developed under laboratory conditions. These models are not designed to be used

8/6/2019 Fact Sheet SMkt Grg

3/10

beyond the range of data used to construct them.

Fact Sheet

The shelf life of foods

. Background

. Factors influencing shelf life

. Food-packaging interaction

. Challenge studies

. Domestic storageFactors influencing shelf l ifePage 2 of 5

No single factor may determine the shelf life of a food but the most important to beconsidered in shelf life studies are:

Microbiological changesMoisture and water vapour transfer

Chemical or biochemical changes

M icrobiological changes

Unless a food has undergone a commercial sterilisation process (e.g. canned foods) or has a

water activity which will not permit microbial growth (e.g. sugar, breakfast cereals), the rateof growth of spoilage microorganisms is likely to be the major factor determining shelf life.

This rate is determined by a number of factors including:

food properties (e.g. pH, total acidity, water activity, presence of preservatives eithernatural or added)

environmental factors (temperature, relative humidity, gaseous atmosphere)any process designed to kill or retard growth of microorganisms (thermal processing,

freezing, packaging)the type of microflora present on the food, and the initial population.

Moisture and water vapour transfer

Not only is water (measured as water activity) a critical factor which determines which, if

any, microorganisms will grow in a food, many foods are sensitive to loss or gain of water.

This in turn can be affected by the choice of packaging and in many instances will determine

which packaging is used.

Many biscuits and savoury snacks including nuts suffer in quality as a result of moisture

8/6/2019 Fact Sheet SMkt Grg

4/10

gain. Some baked foods such as cakes may suffer from moisture loss.

Chemical or biochemical changesWhile freezing arrests microbial activity, chemical reactions proceed at a much reduced rate

even at recommended storage temperatures.

Numerous possible reactions which could limit shelf life fall into this category.

The most important are oxidation, non-enzymic browning, enzymic browning and, in some

cases, food and packaging interaction.

Oxidation of fats and oils leads to the development of rancidity marked by off odour andflavour.

This may limit the shelf life of fats and oils but can also limit the shelf life of many other

foods containing fats and oils. Examples of foods stored at ambient temperatures which can

develop rancid off flavours are nuts, potato crisps and biscuits.

Storage of these foods in high oxygen atmospheres can sometimes be used to accelerate shelflife studies but atmospheric oxygen is not the only initiator of oxidative spoilage.

Many frozen foods can also have their shelf life limited by fat oxidation.

While freezing arrests microbial activity, chemical reactions proceed at a much reduced rate

even at recommended storage temperatures. Examples of frozen foods whose storage life islimited by oxidation include fish and meats.

A number of different vitamins are sensitive to oxygen including vitamin C (ascorbic acid)and vitamin B (thiamine).

When vitamins are added to fortified foods such as breakfast cereals or sports drinks and a

label declaration made, then shelf life determinations will have to take account of anyvitamin degradation which will occur with time in addition to any other changes in quality.

Food-packaging interaction

Page 3 of 5

Most food products rely on their particular packaging to achieve

their expected shelf life.

8/6/2019 Fact Sheet SMkt Grg

5/10

In some circumstances the desired shelf life can be a major factor in

the selection of a packaging material.

For example, if for a particular market segment, the manufacturerof a snack food packed under a modified atmosphere determines

that a shelf life of only six weeks is necessary, it may be possible for

the product to be successfully packed in a plastic with lesser barrier

properties than if the manufacturer was seeking a six month shelf

life.

In either case, the expected shelf life will be dependant on the

integrity of the package seal to maintain the atmosphere within the

package (beyond any expected gas transmission across the

packaging film) for the nominated shelf life.

A special case of food and packaging interaction is the use of tin

plate cans with welded side seams in the canning industry.

While food standards limit the concentration of certain metals in all

foods for public health reasons, there is a maximum tin content

requirement for canned foods of 250mg/kg.

Changes will occur at storage temperatures between 0 C and 5 C

both as a result of microbial activity and chemical reaction.

Most canned foods are now processed in lacquered cans which

substantially reduces the possibility of tin dissolution in the food.

However tin dissolution from the can is essential in some canned

foods which would otherwise be subject to discolouration.

8/6/2019 Fact Sheet SMkt Grg

6/10

Asparagus is one example of such a food. Sufficient tin is therefore

left exposed in such canned foods to ensure the expected quality of

the food through its nominated storage life without it exceeding the

regulatory limit.

Food safety and shelf life

All shelf life studies includes an assessment of the safety of the

product and this assessment will normally precede any assessment

of shelf life.

It is widely recognised that the most effective way to ensure food

safety is to meet the internationally recognised Hazard Analysis and

Critical Control Point (HACCP) system as adopted by the Codex

Alimentarius Commission and written into legislation in many

countries including Australia.

Standard 3.2.1 of the Food Standards Code, Food Safety Programs,

which is based on the HACCP system, is being progressively

introduced into food businesses in Australia based on risk ranking

by Commonwealth and State authorities.

Standard 3.2.2, which has been introduced throughout Australia, is

titled Food Safety Practices and General Requirements, and says in

part, 'this standard sets out specific requirements for food

businesses and food handlers that, if complied with, will ensure fooddoes not become unsafe and unsuitable'.

The most important of these is the requirement that potentially

hazardous foods be stored below 5 C throughout their storage life.

8/6/2019 Fact Sheet SMkt Grg

7/10

Correct temperature storage of chilled foods will not prevent their

becoming 'unsuitable'.

Changes will occur at storage temperatures between 0 C and 5 Cboth as a result of microbial activity and chemical reaction.

These will ultimately limit the shelf life of the food and determine its

best-before date.

Because of the wide range of foods in this category, which includes

cook-chill foods, shelf life studies and safety evaluations are usually

assessed via a challenge study rather than from accumulated

knowledge as is the case with most frozen foods.

Challenge studies

Page 4 of 5

Challenge testing is a laboratory investigation to determine what

can happen to a food product during processing and storage

following inoculation with one or more appropriate microorganisms.

A challenge study is most frequently used to determine if pathogens

will be controlled or to estimate the time it takes for them to grow

to potentially hazardous levels, but can also be used for shelf lifestudies using potential spoilage organisms.

This is particularly so for acid products which receive no

pasteurisation.

8/6/2019 Fact Sheet SMkt Grg

8/10

Challenge testing is a specialised procedure that is time consuming

and expensive but it remains an important procedure in both safety

studies and shelf life determination.

Challenge testing is a specialised procedure that is time consuming

and expensive but it remains an important procedure in both safety

studies and shelf life determination.

Using chilled foods as an example, the aim of a shelf life test should

be to measure as far as possible the acceptable life of the product

under conditions of time and temperature likely to be encountered

during manufacture, distribution, retail storage and in the

consumer's hands.

Standard 3.2.2 requires that foods in this category, if they can

support the growth of pathogens, must be stored at 5 C or lower.

Therefore 5 C is the obvious baseline temperature to use during

storage trials. However the effect of temperatures fluctuating above

5 C needs examination as the possibility of this occurring in actual

practice is very real. It is obviously impossible to duplicate the

whole range of temperature abuse which might occur in a product's

life time.

A shelf life estimate made at, for example, 8 C is likely to vary

significantly from an estimate made at 5 C and some judgmentmust be exercised in reconciling the two figures.

It is essential that a cautious approach be taken until significant real

life data can be assessed. Any challenge test will only yield a

8/6/2019 Fact Sheet SMkt Grg

9/10

specific result for the samples under test and the conditions under

which the test was conducted.

Domestic storage

Page 5 of 5

Most shoppers look for the open date marking on foods in retail

stores.

This is especially the case with short shelf life products usually those

purchased from the chill cabinet.

They should also check carefully the required storage conditions and

endeavour to maintain these as closely as possible on the journey

home (see our fact sheet on Handling food in the home).

The shelf life as determined by the manufacturer applies to theunopened container.

When a container is opened in the home and not all of its contents

used at a single time, the excess should be returned as quickly as

possible to the manufacturer's recommended storage conditions.

Some manufacturers will include in their label recommendations for

handling the product after opening with regard to time and

temperature.

If they do not, the onus is on the consumer to handle the product

hygienically, store it at recommended temperatures and use it

8/6/2019 Fact Sheet SMkt Grg

10/10

within a reasonable time, certainly within the time frame specified

by the manufacturer for the unopened container.

Read more about Food Quality & Safety.