Unless special methods are used to preserve them, the majority of foods available to us are quick to decompose or rot — a result of the action of micro-organisms and enzymes. Preserving food from natural deterioration following harvest or slaughter dates back to prehistoric times. Some of the oldest forms of preservation include cold storage, fermentation and drying. Dried foods such as dates and figs were well known to the ancient hunters and gatherers, who also used the deep recesses of caves and other cold places for the storage of their food. The early Egyptians carried out the processes of fermentation and pickling. We know this from archaeological evidence found in the tombs of the Pharaohs.
In the industrialised society of today, we have moved away from the farming cycle of planting and harvesting. With a great percentage of the population living in an urban environment, there is a need to preserve and process our food to allow for easier distribution and transport.
Raw foods are quick to spoil as a result of the action of food spoilage organisms, enzymic reactions within the food, or environmental conditions. Whatever the cause, spoilage will surely occur unless some preservative action is taken to slow or stop the progress of the spoilage.
The main reasons for preserving foods are to:
– Promote safety
– Keep foods in a form acceptable to the consumer and therefore prevent waste
– Retain the nutritional value of the food
– Make perishable foods available all year round
– Achieve economies for the production company.
Let us discuss this last reason in more detail by looking at an example. If corn was sold in stores only as fresh corn on the cob, rather than as preserved corn that has been frozen, canned or dried, corn farmers would have to reduce the quantity of corn grown and charge more for it. Judging exactly how much to grow would be difficult, and more than likely there would be either a shortage or an oversupply that would rot. It is cheaper to produce a large amount of something than a small amount: this is referred to as the economies of scale. To go back to the corn example, given that the same pieces of equipment are used to plant, water, fertilise and harvest both a small amount and a large amount of corn, it is more economical to keep the machines working for longer periods.
Causes of food spoilage
Spoilage of a food product is caused by one or more of the following:
1. Physical damage can occur when a product is being transported or moved. Examples include the bruising of fruit, denting of cans and wilting of vegetables.
2. Enzymic activity is involved in the ripening and eventual breakdown of fruit and vegetables, and the decomposition of meat. Enzymes exist naturally in both plants and animals and have important functions while the organism is alive. However, once the fruit has been picked, the vegetable harvested and the animal slaughtered, enzymes continue to work, causing spoilage of the food. When fruits are physically damaged, the bruise is the result of enzymes being released from their cells and causing reactions with the cells around them, and with the air.
3. Microbial activity by bacteria, viruses, yeasts and moulds (already present on the product or from the surrounding environment) causes food to spoil. Examples are mould on old bread and sliminess on ageing meat. Microbes will be discussed in depth shortly.
4. Rodent activity or the infestation of bugs and other animals. Good examples are weevils in flour and grain, and mice and rats chewing through food packaging.
5. Environmental factors include warm temperatures, air, moisture and light. These factors speed up the rate of spoilage from other causes, for example, in warm environments enzymes and microbes are more active and oxidative reactions occur quickly.
Preserving food safely
You will recall that the conditions that encourage food spoilage by microbes and enzymes include:
• Warm temperatures
• Available water
• A suitable pH
• A suitable food source.