Home > A Guide to Calculating the Shelf-Life of Foods

What is shelf life?

Shelf life is a guide for the consumer of the period of time that food can be kept before it starts to deteriorate, provided any stated storage conditions have been followed.

The shelf life of a product begins from the time the food is prepared or manufactured. Its length is dependent on many factors including the types of ingredients, manufacturing process, type of packaging and how the food is stored. It is indicated by labelling the product with a date mark.

Is the shelf life of food related to food safety?

Shelf-life testing describes how long a food will retain its quality during storage. Controlling the pathogen content (safety) of foods should be achieved by using a Hazard Analysis Critical Control Point (HACCP) system. Predictive modelling or challenge testing can be used to assess pathogen growth. However, food safety and product shelf life are inextricably linked. During the shelf life of a food, it should:

• Remain safe to eat
• Keep its appearance, odour, texture and flavour
• Meet any nutritional claims provided on the label.

What are the regulations relating to shelf life?

The Australia New Zealand Food Standards Code defines composition and labelling requirements for all food sold in New Zealand.

The shelf life is defined in Standard 1.2.5, which requires that any packaged food with a shelf life of less than two years be labelled with a date mark.

The Code requires food to be safe up to, and including, the date marked.

One of the following options must be used:

• A “Use by” date. This is used for highly perishable foods that will present a safety risk if consumed after this date. A food must not be sold if it is past its “Use by” date, nor should it be consumed.
• A “Best before” date. This is used for foods other than those specified above. It is not illegal to sell food that has reached its “Best before” date.
• “Baked on” and “Baked for” date marks can be used on bread products with a shelf life of less than 7 days. The “Baked for” date must be no later than 12 hours after the bread was baked.

What does the date mark look like?

The words “Use by”, “Best before”, or “Baked on” must be followed by a date or a reference to where on the package the date is located. The date must have:

• At least the day and the month for products with a shelf life of up to three months e.g., Best before 24 Jan
• At least the month and the year for products with a shelf life over three months e.g., JAN 05
• The dates must be expressed numerically and chronologically (day month year) but the month can be expressed in letters. These must be uncoded.
• “Packed on” dates or packer’s codes can be used but only in addition to the date marks described above.

The Code also states:

• Specific storage instructions must be included on the label where these are necessary to ensure the food will keep for the specified period indicated by the date marking.
• Storage conditions must be achievable in the distribution and retail systems and in the home.
• The seller must store the food according to stated storage instructions.

Consideration also needs to be given to providing directions for use and storage after opening. This is particularly important for foods preserved by modified atmospheres or under vacuum where the sealed packaging has a significant influence on the product’s shelf life. For example, sliced ham in vacuum packaging may have a one month refrigerated shelf life, however, once the package is opened it should not be held for longer than 3-4 days.

Who is responsible for calculating a shelf life?

Anyone who packages and sells food that is required to be date marked is legally responsible for calculating how long their product can reasonably be expected to keep, without any appreciable change in quality. The food label is required to detail the shelf life and the storage instructions to meet that shelf life. In most cases, this is the responsibility of the food manufacturer, but it can also be repackers, secondary processors, food retailers and supermarkets.

Who influences the shelf life?

Everyone in this food production chain has an influence on food quality and safety. It is not possible to be confident that food is safe unless a food control plan is in place that identifies and controls hazards throughout the food chain. The role of each person in the food chain should be considered.

GROWERS AND PRIMARY PRODUCERS… provide the raw materials. Variable quality of these can make production of a consistent final product difficult. Consistent quality can be maintained by developing raw material specifications.

OTHER SUPPLIERS… for example, of packaging materials or ice for chilling also have a responsibility to supply safe and consistent materials. They may also provide advice about different materials and their effect on shelf life.

MANUFACTURERS… are responsible for determining a suitable shelf life for their products. This should be based on a study that considers all stages of the production chain.

DISTRIBUTORS… transport the food product from the manufacturer to the retailer. It is essential that food is stored safely and securely in the warehouse, transported at the correct temperature, delays are avoided, and packaging is not damaged.

Consideration should also be given to the possibility of contamination of the food from other goods carried in the vehicle.

RETAILERS… store and handle the product immediately before it reaches the consumer. They must store products according to directions that the manufacturer supplies.

CONSUMERS… are the final link in the chain and it is important that they are provided with the correct information on storage conditions.

Factors influencing the shelf life of a product

How long a shelf life should my product have? There is no simple answer to this question. All foods spoil with time, but there is considerable variation in spoilage rates. Some of the factors involved in loss of quality are explained below.

MICROBIAL GROWTH… the growth of some bacteria, yeasts and moulds in food may lead to either food spoilage or food poisoning.

The time taken for microorganisms to affect foods will depend on their levels in the food when it is produced, as well as any further contamination the food may suffer during packing, storage and other handling. The temperature and time of storage, as well as the type of food, are also important factors. Moist foods will usually spoil faster than dry foods.

Definition of the end of shelf life is usually based on numbers of microorganisms present or on recommended guidance (FSANZ criteria are detailed later in this booklet). In other cases, the end of shelf life may be determined by sensory or biochemical deterioration.

NON-MICROBIAL SPOILAGE… there are many other ways in which quality and nutrients can be lost. They may not necessarily result in the product being harmful but can mean that it is no longer of an acceptable standard.

Moisture gain/loss can result in loss of nutrients, browning and rancidity. Dry foods can become vulnerable to microbial spoilage if they take on moisture.

Chemical change can result in off flavours, colour changes, browning and loss of nutrients. Light induced change can cause rancidity, vitamin loss and fading of natural colours.

Temperature changes increase or decrease the speed of other forms of spoilage.

Physical damage to food can result in spoilage, for example bruising of fruit and vegetables. Damage to food packaging can make the food vulnerable to both microbial and non-microbial spoilage. For example, pin holes in cans or tears in plastic bags allow microorganisms to enter the food and moisture to be lost from the food.

Other

• Spoilage by rodents and insects
• Flavours and odours from storing food near other strongly smelling products
• Product tampering

What is a shelf-life study?

A shelf-life study is an objective, methodical means to determine long a food product can reasonably be expected to keep for, without any appreciable change in quality. A separate study needs to be carried out for each type of product.

The two main methods used are:

1. Direct method This is the one most commonly used. It involves storing the product under preselected conditions for a period of time longer than the expected shelf life and checking the product at regular intervals to see when it begins to spoil. The exact procedure is unique for each product. Details of the steps required and types of decisions to be made are discussed in the following pages.
2. Indirect method This approach uses accelerated storage and/or predictive microbiological modelling to determine a shelf life. A brief outline of these is given later.

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