Methods of food preservation and packaging used in manufacture, including the principles behind each method, their effect on the properties of food, and their role in shelf life, safety and distribution

What this dot point is asking

This dot point asks you to explain how manufacturers preserve food and why they package it the way they do. You need to understand the scientific principle behind each preservation method, how each method affects the sensory, nutritional and functional properties of food, and how packaging works alongside preservation to extend shelf life, protect quality and enable distribution. Strong answers link the principle to a real product and explain the trade-offs.

The principle of preservation

Food spoils mainly because of microorganisms (bacteria, yeasts, moulds) and naturally occurring enzymes. Preservation works by removing or limiting the conditions these agents need: warmth, water, nutrients, oxygen and a near-neutral pH. By altering one or more of these, manufacturers slow or stop spoilage and extend shelf life while keeping food safe.

Heat-based methods

Pasteurisation uses moderate heat (for example 72 degrees Celsius for 15 seconds for milk) to destroy pathogenic microorganisms while preserving flavour, but it does not kill all spoilage organisms, so the product still needs refrigeration. Sterilisation and canning use higher temperatures to destroy all microorganisms and their spores, giving long shelf life at room temperature, though intense heat can soften texture and reduce heat-sensitive vitamins such as vitamin C. Ultra-high-temperature (UHT) processing heats liquids very briefly to a very high temperature, allowing long-life milk to be stored unopened without refrigeration.

Cold-based methods

Chilling slows microbial growth and enzyme activity without stopping them, extending shelf life by days. Freezing turns water into ice, lowering water activity so microorganisms cannot grow, and can preserve food for months; however, ice-crystal formation can damage cell structure, softening texture on thawing. Cold methods preserve most nutrients and sensory qualities well, which is why frozen vegetables retain colour and vitamins.

Dehydration and chemical methods

Dehydration (drying, freeze-drying, spray-drying) removes water to lower water activity below the level microorganisms need, as in dried fruit, powdered milk or instant coffee. Chemical preservation alters the environment: salting and sugaring draw water out by osmosis, acids such as vinegar lower pH below the range bacteria tolerate, and approved additives such as preservatives and antioxidants inhibit spoilage and rancidity. Irradiation exposes food to controlled doses of ionising radiation to kill microorganisms and pests, and is permitted in Australia for specified foods such as some herbs and tropical fruits under the Food Standards Code.

The role of packaging

Packaging protects the preserved food and maintains the benefit of preservation. It provides a barrier against microorganisms, moisture, oxygen and light, prevents physical damage, and contains the product for transport. Specialised techniques extend shelf life further: vacuum packaging removes air to slow aerobic spoilage, and modified atmosphere packaging (MAP) replaces the air inside with a controlled gas mix, for example to keep fresh meat red or salad crisp. Active packaging may absorb oxygen or moisture. Packaging also carries the labelling required by law and influences consumer appeal, while raising sustainability questions about waste and recyclability.