Hot and Cold Food Preservation
Introduction to Hot and Cold Food Preservation Methods
Fruits and vegetables are perishable commodities. If not stored at recommended temperatures after harvesting, they rot in a short time by chemical reactions, bacterial attack, or water loss. Improperly stored fruits and vegetables lose nutrition value over a period of time. Changed physical appearance or taste also affects their consumer appeal. Refrigeration helps in preserving fruits and vegetables by storing at low temperatures to slow down decay and natural metabolic processes.
Meat, fish products, and precooked foods also have limited life because of enzyme activities, bacteria attack, and ageing. Low temperature is very effective in limiting these reactions.
Similarly, ice cream, other dairy products, bakery products, and beverages need to be stored at low temperatures for long-term use.
Food preservation was present in every culture throughout history. For survival, ancient civilisations had to harness nature in the absence of modern day refrigeration units. In frozen climates, meats were frozen on ice and in hot climates; foods were laid out and dried in the hot sun.
Food begins to spoil from the moment it is harvested. By developing food preservation techniques, it enabled communities to settle in one place as the kill or harvest did not have to be consumed immediately but could preserve for later use. Consequently, a daily hunting or foraging expedition and nomadic living searching for food was not necessary.
Drying is one of the oldest methods of preservation and sun and wind would have naturally dried foods. Evidence shows that food drying was active as long ago as 12,000 BC. All cultures would have their own methods of drying for fish, game, and domestic animals. Vegetables and fruits are dried today such as sun-dried tomatoes, raisins, currants, apricots, cherries and so forth. Drying techniques have moved on but it is still possible to buy naturally sun-dried produce. The Romans were particularly fond of any dried fruit they could make. In the Middle Ages purpose built sheds were designed to dry fruits, vegetables and herbs in areas that did not have enough sunlight for drying. A fire created the essential heat to dry foods and some produce was smoked.
Freezing was an obvious preservation method in the appropriate climates. Any geographic area that had freezing temperatures for even part of a year made use of the sub-zero temperature to preserve food. Other cooling methods using cellars, caves and cool rivers and streams were used when the temperatures rose above freezing.
Icehouses were used to store ice throughout the year, commonly used prior to the invention of the refrigerator. Some were underground chambers, usually man-made, close to natural sources of winter ice such as freshwater lakes, but many were buildings with various types of insulation. During the winter, ice and snow would be taken into the icehouse and packed with insulation, often sawdust, or straw. The ice would remain frozen for many months, often until the following winter, and was used as a source of ice during summer months.
Many large estates had icehouses until the 1800’s when mechanical refrigeration was invented. In the late 1800’s Clarence Birdseye discovered quick freezing at very low temperatures made meat and vegetables taste better, perfected his quick freeze process, and revolutionised food preservation.
Today refrigeration engineers are highly qualified and accredited to handle the complex refrigerants used in air conditioning and refrigeration units. Unlike the refrigeration engineers of yesteryear who used a pick to gather ice chunks for the icehouse, today’s experts are likely to have computers and sophisticated knowledge of chemistry.