Food Technology – Food Preservation
Most fresh foods spoil soon after production or harvest. Because of this, people have sought ways to preserve perishable foods since the beginning of human history.
The changes we observe in natural products as they decay are mainly the work of bacteria, yeast, or mold. These microorganisms draw nourishment from the food and then multiply. In so doing, they change the characteristics of the food: for instance, it may become mushy, foul smelling, or moldy. In most cases, people view these changes as undesirable and attempt to stop or at least slow them.
Numerous preservation methods have been developed to suppress the activity of microorganisms in foodstuffs. In general, these can be divided into physical, biological, and chemical techniques. Some processes, such as sterilization, all microorganisms in a substance are destroyed. Other methods (such as the pasteurization and refrigeration of milk) merely slow their growth, so that the food retains its quality for a certain length of time.
Radical methods that destroy all microorganisms may be highly effective, but they are not always the best solution, as they can negatively affect the food’s taste, nutritional value and texture.
Physical methods
One of the oldest food conservation techniques is drying. Dried foods can be safely stored for long periods, since the lack of water prevents microorganisms from reproducing. The oldest and simplest method is air drying. Food in canning jars or metal cans is preserved through the use of heat, which destroys all of the microorganisms within the food.
However, the longer a food is heated, and the higher the temperature used, the more the quality of the food will suffer. Accordingly, gentler techniques have been developed, such as pasteurization (see milestones).
With refrigeration and freezing, the growth of bacteria and other organisms is sharply reduced, while many frozen foods remain quite similar to the fresh product after thawing. Microorganisms can also be destroyed with ionizing radiation (irradiation).
Biological, chemical, and other techniques
In some foods, the natural changes caused by microorganisms are considered desirable. For example, if fresh milk is left out in the open, certain types of bacteria will feed on its sugars, producing lactic acid and suppressing the growth of other unwanted microorganisms (and converting the milk to yogurt).
In alcoholic fermentation, yeast populations expand and give off alcohol, which has a preservative effect. Chemical preservatives can also be used to prevent bacterial growth. The use of nitrites to preserve meat products is wide- spread. Other well-known chemical preservatives include benzoic acid and sorbic acid. Food can also be preserved by smoking or salting it, or by adding sugar.
PASTEURIZATION
Louis Pasteur discovered that most food-borne micro-organisms can be destroyed by briefly heating the food to 140-158°F (60-70°C) This method, which became known as pasteurization, is still commonly used to preserve liquid foods.
For instance, milk is heated to about 161-167°F (72-77°C) for 15 to 40 seconds. Yet the results are not completely sterile, and consequently, they remain fresh only for a limited time.
BASICS
FOOD PRESERVATION TECHNIQUES PHYSICAL methods: water removal (drying), heating, refrigeration, freezing, irradiation
BIOLOGICAL methods: fermentation (e.g., alcoholic)
CHEMICAL methods: addition of chemical preservatives
OTHER methods: smoking, salting, addition of sugar