Since the beginning of civilization people have searched for ways to safely store food. All kinds of preserving processes have been used including drying, salt curing, and canning. All of these processes greatly alter the taste and nutritional value of foods hence does not fully serve the purpose of storing food.
Before the invention of the refrigerator, icehouses were used to provide cool storage for most of the year. They would be placed near freshwater lakes or packed with snow and ice during the winter, and were once very common. Natural means are still used to cool foods today. On mountainsides, runoff from melting snow is a convenient way to cool drinks, and during the winter one can keep milk fresh much longer just by keeping it outdoors.
By the mid-1800's scientists discovered that storing food at a low temperature inhibited growth of bacteria and fungus without altering the food itself too much, and the idea of the modern refrigerator was born. The refrigerator is one of the miracles of modern living that totally changed lifestyles, and leftovers could be saved for another meal without wastage!
The first known artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in 1748. In 1834 American inventor Jacob Perkins created the cooling compression system that made in-home refrigeration possible. Unfortunately, Perkins' system used poisonous gasses to create the cooling process and many consumers died as a result of accidentally inhaling these gasses. In 1857, Australian James Harrison developed the world’s first practical ice making machine and refrigeration system. Ferdinand Carré of France developed a somewhat more complex system in 1859. Unlike earlier machines, which used air as a coolant, Carré's equipment used rapidly expanding ammonia. By 1920 there were more than two hundred different models of refrigerators available.
The introduction of Freon (this is a compound which combines several nontoxic chlorofluorocarbons ) in the 1920s expanded the refrigerator market during the 1930s and provided a safer, low-toxicity alternative to previously used refrigerants. Separate freezers became common during the 1940’s, which was known as the "deep freeze”. These devices did not go into mass production for use in the home until after World War II. In 1947 General Electric introduced the two-door refrigerator/freezer combination that is the standard design for all modern refrigerators.
The 1950s and 1960s saw technical advances like automatic defrosting and automatic ice making. More efficient refrigerators were developed in the 1970s and 1980s, even though environmental issues led to the banning of very effective (Freon) refrigerants.
In today's world the refrigerator is more environmentally friendly and uses tetrafluoroethane, or HFC as a refrigerant. Newer refrigerants are being used too; the main refrigerant now used is R-600a, or Isobutane. This refrigerant is naturally occurring and therefore has a smaller effect on the atmosphere, if released, hence more environment friendly.
With a refrigerator at home, visits to the grocer or butcher have reduced as people have started to store their requirements for a week or so. Refrigerators address very diverse demands, and are now available in hundreds of different sizes and styles, in varying prices too.
A vintage refrigerator [Image source]
The process of refrigeration requires two important factors: the fact that a gas cools as it expands and the Second Law of Thermodynamics, which states that when two objects are near each other, the warmer one cools and the cooler one warms up.
Thermodynamics: A motor and compressor are used to constrict the gas HFC, as a result this heats up. The gas is then sent through coils in the refrigerator which allow the heat of the gas to escape and the HFC to change into a liquid. The liquid travels through an expansion valve and then continues through the coils and draws heat from the compartments, then flows into a low pressure area, which allows it to boil and return to a gas.
The process then begins again and the cycle continues.
Refrigerator Parts: The refrigerator contains six important components which are vital to the completion of the process.
The refrigerant, or the HFC, is the first vital component and without this gas, the process would be non-existent.
The evaporator is the component that absorbs heat in the refrigerator using the refrigerant.
The heat changing pipes or coils transfer the refrigerant throughout the refrigerator.
The compressor is made of metal and is powered by a motor. It is used to increase pressure and therefore temperature for the refrigerant.
The condenser is also very important component. It exerts pressure on the refrigerant, causing it to change into a liquid and therefore cool down.
The expansion valve, which is made of thin copper wire, is used to reduce pressure on the refrigerant.
Therefore the process of refrigeration depends more on the extraction of warm air from the area surrounding an object and on evaporation than on a process that lowers the temperature of the object that is being cooled. A refrigerator is an example of a closed system, which means that nothing is gained or lost during the process of refrigeration. Instead, all gas is contained to be used by the system again.
Earlier refrigerators had latched doors. More modern units use a magnetic door gasket which holds the door sealed.
Average Food Life in Refrigerator
Proper home storage can extend the shelf life of most foods, and prevent the growth of bacteria that can cause food-borne diseases. The refrigerator should always be kept below 40 degrees (F), with the freezer set to 0 degrees (F). Individual foods have different requirements for storage, but in most cases any change in colour or texture, or an appearance of slime indicates spoilage.
Fresh vegetables can be stored up to five days at 35-40 degrees (F) in moisture-proof bags. The crisper drawer is the best place for vegetables because the humidity is regulated for optimum storage. Root vegetables (onions, potatoes, etc) should be kept at in a cool, well-ventilated place at 50-60(F) degrees (not in the refrigerator). Tomatoes continue to ripen after they are picked, so they should be stored at room temperature.
Fresh fruit can be kept up to five days at 35-40(F) degrees, except strawberries, which are only good for three days. Citrus fruits can be stored for up to two weeks, and apples can be kept in the refrigerator for up to one month. Bananas turn brown when refrigerated, so they are best kept at room temperature.
Dairy Products should be stored between 34-38(F) degrees. Milk can be kept for up to eight days, and cheese can be kept until moldy. All cheese should be tightly wrapped in plastic to prevent moisture loss.
Meat, eggs, and fish should be stored between 33-36(F) degrees. Fresh meat should be used within three days, while cured meats can be stored for up to a week.
Poultry should also be used or frozen within 24 hours, while eggs can be stored for 3-5 weeks from the "pack date" on the carton. Always keep eggs in their original carton - this protects them from odours, breakage, and contamination by other foods.
Fish and shellfish must be used or frozen within two days. Live shellfish (clams, mussels, etc.) should be stored in an open container and covered with a damp cloth, while fish should always be tightly wrapped in plastic.
Types of Refrigerators
Domestic refrigerators and freezers for food storage are made in a range of sizes. Fridges and freezers may be free-standing, or built into a kitchen. Some models for small households fit under kitchen work surfaces. Fridges may be combined with freezers, either stacked with fridge or freezer above, below, or side by side. A fridge without a frozen food storage compartment may have a small section just to make ice cubes. Freezers may have drawers to store food in, or they may have no divisions (chest freezers).
Newer refrigerators may include:
There are many types of refrigerators too depending on the type of heat source they use.
Some examples are: Compressor type, absorption type, refrigerators that run on oil, gas (natural gas or propane), solar refrigerators and thermal mass refrigerators (these are designed to reduce consumption of electricity), magnetic refrigerators that work on magneto caloric effect, acoustic refrigerators that use resonant linear reciprocating motors/alternators to generate a sound which is then converted to heat and cold using compressed helium gas.
Refrigerators in India
Refrigerators in India are designed keeping in mind the tropical climate of India. More than 8 months of the year, 90% India faces hot humid weather. And hence, refrigerators are used in almost all households. Sale of refrigerators in India has touched new high in the recent few years as the living standards of the people have improved and refrigerator prices are now more affordable. Refrigerators for home as well as industrial use can be bought in budget starting from less than 20,000 rupees to over 1,10,000 Rupees. Refrigerators with/without freezers and separate freezers are also available with the retail stores.
A voltage stabiliser is used along with a refrigerator in most parts of India. This is to take care of the voltage fluctuations that are common in the power supplied. If these kinds of precautions are not taken the refrigerators will break down.
The types of refrigerators available in the Indian market are:
Different capacities of refrigerators may range from 300 to 650 litres. One can store large amount of food in these refrigerators.
The Indian buyers seek complete information about the refrigerators before purchasing. They prefer the best deals that give them complete value for money. Comparisons between refrigerators are made on the basis of the utility features like:
and additional features like:
Refrigerators in India are also given an “Energy Star” rating which indicates their energy efficiency.
Some examples are presented below:
This 180 litres, 1 door refrigerator shown above has a 30 litres freezer capacity has a semi automatic defrost system. It has 8 shelves and boxes, which are adjustable and has a door lock with door open alarm. It has feature of moisture and humidity control and deodoriser. It comes with Utility Drawer which is situated the bottom where one can store vegetables like potatoes and onions, which do not require refrigeration and so one can find all vegetables at one place.
The above example of a refrigerator has “6th Sense Fast Forward Ice System”, which gives superior cooling that helps make ice super fast. It also has roomy trays and shelves and separate section for different food items along with many features.
A small double door refrigerator [Image source]
A triple door refrigerator [Image source]
Multi door refrigerator with water dispenser feature
Refregerators in Rural India
India hosts the world’s largest population deprived of electricity. Ninety two percent of this population lives in rural India, equalling about 380 million people or 71.7 million households. The quality and quantity of power these people have access to is very poor and there is very little development happening in rural areas.
The power situation in rural India cannot be fixed overnight and until that time, products are needed to make people's lives a little better. Effective refrigeration in rural areas can help people extend their access to not only food, but also essential drugs. The price barrier is what prevents refrigerators from becoming a household item in rural India. So a number of companies and individuals are trying to overcome these limitations and bring in solutions. It helps to come up with grass root solutions for rural products created with local ingenuity.
1. Voltas India Ltd. has launched a 65-L, direct-cool refrigerator that is specially designed to cater to rural needs - it can store heavy utensils, has tough insulation, and has built-in stabilizers to cope with high-voltage fluctuations. Also it comes at a very low price of Rs 5,000.
2. Indian conglomerate Godrej and Boyce has introduced, ChotuKool another example of a cheap refrigerator. This portable, top-opening unit weighs only 7.8kg, uses high-end insulation to stay cool for hours without power and consumes half the energy used by regular refrigerators. This is a product that has crossed several technological barriers and several social barriers as well.
The ChotuKool doesn't use a compressor, instead runs on a cooling chip and a fan similar to those used in computers, so like computers it can run on batteries. It’s engineering credentials are further boosted by the fact that it has only 20 parts, as opposed to more than 200 parts in a normal refrigerator.
The ChotuKool was co-designed with village women to assure its acceptability, and is distributed by members of a micro-finance group.
ChotuKool [Image source]
ChotuKool being taken for field testing in rural India [Image source]
3.Mansukhbhai Prajapati comes from a family of potters; he developed Mitticool another example of a rural refrigerator.His efforts were noticed by the Honey Bee network, which has done an amazing job of connecting grassroots innovators in India. Through their partner organization GIAN (Grassroots Innovation Augmentation Network) he was put in touch with designers at the National Institute of Design.
Together, they came up with the present form of Mitticool, which is a juxtaposition of the traditional and the modern. It has a clay exterior, with a plastic tap and shelves to hold the food items. The rural innovator and urban designers have come up with an object that looks like it will be very happy to be hawked at any village market, because it manages to exactly capture the tastes of today’s rural Indian.
Mitticool refrigerator [Image source]
4. Another experiment intends to make cheap refrigerators using solar-power in India. Most commercial fridges run on diesel generators, but this new concept intends to make a refrigerator from commonly used car parts so it can be easily repaired in rural areas.
The concept was created by the Solar Turbine Group (STG), a non-profit organisation formed by students from the Massachusetts Institute of Technology. STG has already built some of its solar turbines in the African country of Lesotho, which are used for creating hot water and electricity.
The solar refrigeration system uses parabolic troughs to generate the heat from sunlight to heat a liquid, which creates steam to turn a turbine to make electricity. The goal is to make a system that is also able to work by burning natural gas or biomass, which can be readily available in rural areas.