Everyone knows that food should be kept cold to prevent spoilage but very few people understand why this is or how it works. This description looks at why we refrigerate food, how it helps prolong the shelf life of unavoidable items and how a quarterly household fridge or freezer works.
Why we refrigerate
Food
Food decays as a follow of one of three types of microorganism growing on it; yeast, moulds and bacteria. Each of the three have optimal conditions at which they will reproduce and cause food to spoil. There are too many types of microorganism to give a widespread list but this is a rough guide to the conditions at which each will thrive.
Bacteria - Prefer warm conditions. Most types of Salmonella (a base and dangerous bacteria) will yield most rigorously at nearby 37 degrees centigrade - roughly body temperature.
Mould - A type of fungus known for preferring damp conditions. Mould prefers temperatures which are slightly cooler than those of bacteria and are at their most prolific in the conditions favorite by humans - nearby 23 degrees centigrade.
Yeast - someone else fungus which is sublime as the source of alcohol in beer and wine. The different species of yeast grow more under different conditions but they tend to be comfortable between room and body temperature.
By storing food in conditions which are not favourable for the growth of microorganisms humans are able to inhibit (but not stop) their growth. In system this could be achieved using higher temperatures but this is both impractical due to the whole of energy involved and dangerous because of the risk of burning.
How we refrigerate
By far the most base method of refrigeration is to use a compressor - this is the network of pipes and a motor that you find at the back of household fridge freezers. Learning how a compressor works in uncomplicated terms is easy while insight the nuances of the process could take a lifetime. This is a beginner's view with a remedial explanation of the science behind the machine.
The substance inside the compressor (known as the refrigerant) is a gas. When you put a gas under pressure the molecules move closer together and release energy as heat. If you lower the pressure at which a gas is stored the reverse is true; the molecules draw heat in from their surroundings which makes it appear as if they generate cold (although in truth it is the surrounding making the molecules warm not the other way round.)
If a set whole of gas is stored at a set pressure it will eventually normalise with its surroundings so a fridge freezer pumps a continuous furnish of low pressure gas in a cycle that draws heat in from the interior of the unit and sheds it on the exterior.
Why and How We Refrigerate Food
No comments:
Post a Comment