The Who, What, When, Why and How of Shelf Stability and the Rules for Determining Shelf Life
Published: 15 Dec 2010
Almost all packaged foods with an expected shelf life of less than two years must be date-marked according to Standard 1.2.5 of Australia New Zealand Food Standards Code (ANZFSC).
The few exceptions include food with a best-before date of greater than 2 years; an individual portion of ice cream or ice confection; a small package (except where it should be consumed before a certain date because of health or safety reasons).
The important issue is to establish the answers to the following questions is relation to shelf stability, which determines the “use-by” or “best-before” date:
- Who makes the decision regarding what date appears on the food package?
- What Standards govern this decision?
- When is shelf life testing required?
- Why is date-marking required?
- How is shelf life determined?
Although long life foods with an expected shelf-life of over 2 years do not require mandatory date marking, the shelf life or shelf stability of these foods is still required to be understood and known.
Packaged Food for Retail Sale:
The following discussion applies to food for retail sale that is packaged otherwise than by the retailer and not exempted by clause 2 of Standard 1.2.1 - Application of Labelling and Other Information Requirements.
According to the requirements of this Standard, the food should be and generally is already date-marked prior to delivery to the retail outlet, whether by the manufacturer or the wholesaler/distributor.
Imported packaged foods are often subjected to different rules due to mode of transport, conditions of storage during transport and time elapsed from freight starting to goods received into store.
The date-mark is information to all sections of the supply chain and finally the consumer to inform all parties of the status and expected shelf life of the food.
However it should be noted that the legal responsibility for the health and safety aspects of any food passes to the last person or organisation in the supply chain unless it can be demonstrated that the food has not been handled in the required manner at some stage.
The concept that shelf-life commences once the food package arrives into storage at the final part of the supply chain, usually the consumer, is totally incorrect. Any agricultural (vegetable or animal) product, for which there has been no human intervention, such as harvesting, milking or slaughter, etc, will start to deteriorate naturally when it reaches maturity.
Once a human activity is applied, then deterioration commences, such as oxidation, enzyme activity, microbiological spoilage, chemical changes; notwithstanding any preservation techniques, including freezing, chilling, pasteurisation, etc that may be utilised.
Shelf Life Parameters:
Packaged foods that are prepared on premises, including those made and/or packaged on the site of the retailer, are required to be date-marked. The food industry has accepted the position that the remaining shelf-life of a food product, as indicated by the date marked on a package as ‘use-by’ or ‘best before’, commences at the point of sealing the package.
The life cycle of a packaged food is not only determined by the manner of the food preparation but also by the packaging and the manner the handling at all stages of storage, handling and transport is conducted.
The factors that determine the shelf-life of a packaged food product, with or without a preservative, physical or chemical, include the quality of the starting materials and all the activities involved prior to reaching its final stage as well as air/oxygen, modified atmosphere, temperature, humidity, light, moisture, water activity, microbiological load and packaging materials.
For many years, it was thought that sunlight was the only light source that caused deterioration. However it has been established that all artificial light sources, including fluorescent can have a deleterious effect. For highly sensitive-to-light products the packaging is mainly for protection, hence brown bottles and cardboard boxes for beer; green and brown bottles for wine; multilayer cardboard cartons and now opaque plastic containers for milk; large wrap around labels on soft drink bottles; eggs in cardboard boxes; etc.
Shelf Life Determination:
In many and probably the majority of food manufacturing facilities, the shelf-life of a their products, particularly where there is a low risk of health and safety issues, are not determined scientifically but the shelf-life and the date marking is more often estimated rather than empirically established.
The method of estimation for many years and products was based on expertise, experience in a certain sector of the food manufacturing industry, customer feed back and complaints, competitors labelling (both local and overseas), advice from packaging suppliers (often with international affiliates), etc.
Now, with highly increased requirements, surveillance and enforcement by the supermarket chains in all aspects of food quality, labelling, etc, there is an increase in the need to scientifically verify the shelf life of all food products and to validate the test methods.
For instance, with short-life or “fresh” or seasonal foods that deteriorate or degrade quickly, such as many milk products, fresh fruit and vegetables, bread, meat, fish, etc the supermarket chains, with central delivery and distribution depots, require a prerequisite number of “clear days” before the “use-by” date is reached, presumably for time to distribute the goods to their retail outlets. These “clear days” are counted starting the day after delivery into the distribution centre and if, for example, 4 “clear days” are mandated, then the “use by” date must be at least 5 days after delivery.
The question arises as which test methods are mandated, universal and applicable to the huge variety of food categories and packaging materials.
A search of Australian organisations, such as Food Standards Australia New Zealand (FSANZ), Australian Food and Grocery Council (AFGC) and Standards Australia (SA) has revealed very little in either mandatory requirements or voluntary codes or guidelines.
FSANZ User Guide – Date Marking stated: “The intention of date marking is to provide a guide to consumers on the shelf life of a food in terms of food quality. This means the length of time a food should keep before it begins to deteriorate. In some circumstances, date marking may also indicate how long a food can be expected to remain safe.”
SAI Global offered only one Standard and that was from USA (ASTM), besides the relevant microbiological standards and testing procedures that apply to specific food groups (also see ANZFSC Standard 1.6.1 – Microbiological Limits for Food).
ASTM International published “Standard Guide for Sensory Evaluation Methods to Determine the Sensory Shelf Life of Consumer Products”, Designation E2454 – 05. This guide is based on sensory or organoleptic (flavour, aroma, colour, texture) characteristics.
This Guide is based on the principle that the sensory properties of a food, where all the health and safety issues have been previously addressed, are the most important characteristic. If a food has, even only one, negative sensory property then its market value is severely reduced. In the language of the market place “If it does not taste and smell good, then it is not good” and this is entirely superior and separate from any claimed nutritional benefit.
Although this Guide details accepted sensory tests and provides protocols of time periods to conduct successive tests, it does not provide any actual test methods for any specific product. The testing regime is based on expected shelf-life.
Another publication that attempts to address some of the peripheral issues is “A Global Language for Packaging and Sustainability – A framework and measurement system for our industry” published by the Consumer Goods Forum and available from the Packaging Council of Australia.
Most shelf-life testing is performed in-house and the techniques used remain commercially confidential. Over the years there have been several iconic shelf-life test reports released for the use of any company and these include:
i. “Sensory Assessment of the Shelf Life of Carbonated Soft Drinks” by R. L. McBride and K. C. Richardson CSIRO, 1983
ii. “Light Damage in Milk” by Dr. K. T. H. Farrer, 1984
iii. Vitamin Levels in Fresh Milk by V. Garnys, M Gledden, 1989
Every product, in its full gamut of the various packaging options, will require its own individual testing protocol. The time required to conduct a full time test until the actual shelf life is reached is often a delay that manufacturers do not want to suffer as product launch deadlines are often set prior to the data being available.
Various techniques used to establish the mandatory shelf-life (expiry date) of therapeutic goods have been adopted by the food industry, in lieu of the absence of other published and established methods.
In this regard, the Australian Regulatory Guidelines for OTC Medicines (ARGOM) of 1 July 2003 states:
In most circumstances, the following general rule-of-thumb is used:
If no trends are noted after storage for a period of (x) months at an elevated temperature (at least 10°C above the maximum storage temperature proposed for the product) then an interim shelf life of a maximum of (2x) months may be permitted….
The above indication is often used with elevated temperature to achieve accelerated storage data and hence establish an approximate shelf-life. However accelerated storage or abusive storage conditions often only produce or indicate the worst case scenario and do not always provide a true shelf-life indication.
For a product with an expected shelf life when stored for its whole life cycle at ambient temperature, then testing may consist of 25°C and 80% relative humidity (RH) or 30°C and 75% RH.
Validation for any packaged food product testing regime will consist of actual testing and storage under the normally expected storage, using controlled and measureable conditions for the full expected shelf life time. Manufacturers often conduct this type of full shelf-life testing after a product is launched and then the date-marking is adjusted accordingly.
For short life foods (say less than 3 months) the testing is relatively short whereas for a food with an expected shelf life of 12 to 24 months, this creates time problems, so an interim date mark is provided.
Another aspect of shelf-life testing is the microbiological status of the food. The microbial load at the point of manufacture will determine the possibility of reaching the expected shelf life under the proposed storage conditions. Often either preservatives (mainly chemical) are added, where permitted or a physical method is used to control microbiological growth, i.e. heat including pasteurisation and UHT, temperature reduction including chilling, refrigeration and freezing and, more recently, high pressure.
Challenge testing (sometimes referred to a Preservative Efficacy testing) is employed whereby an excess of a known mixture of food pathogen forming
bacteria are inoculated into the food and the food is then stored under its designated storage conditions for an extended period (about one month for products with an expected shelf life of over 12 months). At the end of the test storage period, the food is analysed to evaluate whether it is still in an acceptable condition microbiologically (i.e. within accepted or mandated limits) and then sensory testing is performed.
There are several independent analytical food laboratories that have the facilities to conduct both microbiological challenge testing and extended shelf life testing under controlled temperature, humidity and time conditions.
For specific compliance advice and technical reviews of food production systems, readers can brief FoodLegal. Our technical expertise is drawn from our in-house and affiliate technical resources. Contact Joe Lederman at FoodLegal <email@example.com>