Friday, August 21, 2009
Stir fry method of cooking is very healthy. It uses less oil and leaves the food crisp and not overly cooked, and thus not stripping out all the nutrients and vitamins from raw food especially vegetables. Stir frying only takes a matter of minutes if you follow these few easy steps.1. Well equippedFirstly, a wok is a must, not pan, a big round wok. A round-based one works well using gas burner while a flat based one works well on electric stoves. A good wok is heavy usually made of cast iron or carbonated steel, easily available is departmental store and Asian hardware shops. Teflon based just doesn't give you the same rich flavor. When first purchased, the iron wok must be seasoned, heat the wok until smoke start rises from the wok, and then pour in a table spoon of peanut oil. Wipe the oil around the wok surface and throw away excessive oil. This way, all dirt will be removed from the wok surface. Secondly, a ladle is a must. Choose one with strong handle. 2. Prepare your ingredientsAll raw meat and vegetable must be cut uniformly in thickness and size in advance. This is to ensure the food is evenly cooked. Once the wok is heated, there is not enough time to cut anymore. Rice and noodles need to be pre-cook, rice to be steamed while noodles to be boiled to soft.3. Seasoning a must. Before cooking the main ingredients, Asian usually put in chopped garlic or shallots to enhance the taste of stir fry dishes. When the wok is heated, oil is put in, then garlic or shallots are put in to fry until golden brown. Only then the main ingredients are put in.4. Meat first, vegetables secondFor stir frying, this is can be considered the golden rule. Always cook meat first, vegetables second. Meat is harder to cook compared to vegetables. If both are cook together, the vegetables tend to overcook. Meat or seafood must be marinated with a pinch of salt first. Always toss the ingredients for even cooking. When stir frying rice or noodles, the goldren rule still applies, always meat first.5. Sauce and seasoningLastly, add sauce to your stir fry dish. Sauces, such as oyster sauce, or sweet and sour, thin and thick black soy sauce are added into the wok to complete the stir fry dish. Oyster sauce, thin and soya sauce is the most common, packaged in bottles and easily bought from the supermarket shelves. Sweet and sour is popular unique but it's just simply tomato sauce and sugar. Simply put in the sauce after the meat and vegetables are cook in the wok, sauté for a while, and the dish is ready to serve.
In the summertime, have you ever gotten out of a swimming pool and then felt very cold standing in the sun? That's because the water on your skin is evaporating. The air carries off the water vapor, and with it some of the heat is being taken away from your skin. This is similar to what happens inside older refrigerators. Instead of water, though, the refrigerator uses chemicals to do the cooling. There are two things that need to be known for refrigeration. 1. A gas cools on expansion. 2. When you have two things that are different temperatures that touch or are near each other, the hotter surface cools and the colder surface warms up. This is a law of physics called the Second Law of Thermodynamics. Old Refrigerators If you look at the back or bottom of an older refrigerator, you'll see a long thin tube that loops back and forth. This tube is connected to a pump, which is powered by an electric motor. Inside the tube is Freon, a type of gas. Freon is the brand name of the gas. This gas, chemically is called Chloro-Flouro-Carbon or CFC. This gas was found to hurt the environment if it leaks from refrigerators. So now, other chemicals are used in a slightly different process (see next section below). CFC starts out as a liquid. The pump pushes the CFC through a lot of coils in the freezer area. There the chemical turns to a vapor. When it does, it soaks up some of the heat that may be in the freezer compartment. As it does this, the coils get colder and the freezer begins to get colder. In the regular part of your refrigerator, there are fewer coils and a larger space. So, less heat is soaked up by the coils and the CFC vapor. The pump then sucks the CFC as a vapor and forces it through thinner pipes which are on the outside of the refrigerator. By compressing it, the CFC turns back into a liquid and heat is given off and is absorbed by the air around it. That's why it might be a little warmer behind or under your refrigerator. Once the CFC passes through the outside coils, the liquid is ready to go back through the freezer and refrigerator over and over. Today's Refrigerators Modern refrigerators don't use CFC. Instead they use ammonia gas. Ammonia gas turns into a liquid when it is cooled to -27 degrees Fahrenheit (-6.5 degrees Celsius). A motor and compressor squeezes the ammonia gas. When it is compressed, a gas heats up as it is pressurized. When you pass the compressed gas through the coils on the back or bottom of a modern refrigerator, the hot ammonia gas can lose its heat to the air in the room.Remember the law of thermodynamics. As it cools, the ammonia gas can change into ammonia liquid because it is under a high pressure. The ammonia liquid flows through what's called an expansion valve, a tiny small hole that the liquid has to squeeze through. Between the valve and the compressor, there is a low-pressure area because the compressor is pulling the ammonia gas out of that side. When the liquid ammonia hits a low pressure area it boils and changes into a gas. This is called vaporizing. The coils then go through the freezer and regular part of the refrigerator where the colder ammonia in the coil pulls the heat out of the compartments. This makes the inside of the freezer and entire refrigerator cold. The compressor sucks up the cold ammonia gas, and the gas goes back through the same process over and over. How Does the Temperature Stay the Same Inside? A device called a thermocouple (it's basically a thermometer) can sense when the temperature in the refrigerator is as cold as you want it to be. When it reaches that temperature, the device shuts off the electricity to the compressor. But the refrigerator is not completely sealed. There are places, like around the doors and where the pipes go through, that can leak a little bit. So when the cold from inside the refrigerator starts to leak out and the heat leaks in, the thermocouple turns the compressor back on to cool the refrigerator off again. That's why you'll hear your refrigerator compressor motor coming on, running for a little while and then turning itself off. Today's refrigerators, however, are very energy efficient. Ones sold today use about one-tenth the amount of electricity of ones that were built 20 years ago. So, if you have an old, old refrigerator, it's better to buy a new one because you'll save money (and energy) over a long period of time. For more information go to: • Argone National Laboratory - Ask A Scientist (http://newton.dep.anl.gov/newton/askasci/1993/eng/ENG30.HTM)• Mr. Hand's 8th Grade Science Site (www.mansfieldct.org/schools/mms/staff/hand/heatrefrig.htm)• How Stuff Works - Refrigerator (www.howstuffworks.com/refrigerator.htm)• Science Treasure Trove - refrigerator page (www.education.eth.net/acads/treasure_trove/refrigerator.htm)
Packing houses serve as a collection centre for fruits and vegetables prior to distribution and marketing. The houses can be simple packing sheds with a limited equipment and minimal operations or a large complex that is well equipped and with facilities for specialized operations. The types of operation carried out vary with different commodities and market requirements. Produce that are destined for export or supermarket outlets are often subjected to elaborate operations compared to local markets. Some of the operations are as follows: Sorting and TrimmingFreshly harvested fruits and vegetables are sorted for uniformity in size, shape and varietal characteristics. Damaged, discoloured and decayed parts are removed to make the produce more attractive and prevent infection from the diseased parts.WashingWashing is necessary to remove extraneous materials from the field such as dirts, chemicals and latex. This is usually done before storage or immediate retailing of the produce. In order to r educe the incident of decay, chlorine is often added to the wash water. DryingDrying is done to remove excessive moisture from the surface of the produce. Excessive drying should be avoided to prevent wilting, shrinking and water loss.WaxingWaxing is done on certain types of fruits and vegetables such as ginger, tomato, citrus and melons to reduce water loss, thereby reducing shriveling. In addition to that, the application of edible wax will enhance the appearance of the produce.CuringInjured and bruised surfaces of root, rhizome and tuberous crops are allowed to heal by holding them at ambient temperatures for a few days. Curing initiates the formation of periderm layers at wound areas, thereby reducing moisture loss and microbial infection. Sufficiently cured vegetables can be stored for a longer period.Chemical TreatmentsFungicides and growth regulators are commonly used to reduce decay and undesirable growth respectively. The use of chemicals should be closely supervised and within the recommended levels for human consumption.GradingFresh fruits and vegetables are classified into groups according to a set of recognized criteria of quality and size, with each bearing an accepted name and size grouping.PackagingProduce are packed in suitable containers to provide protection against mechanical and biological damages during transportation and subsequent handling operations. Packaging materials should be of accepted standards with regard to strength, ruggedness and resistance to pressure. Packages should have adequate ventilation so that produce will not warm up as a result of heat arising from respiration. Excessive ventilation, however, may result in wilting.Pre-coolingPre-cooling is an essential step prior to storage at low temperatures. It is the rapid removal of field heat from the produce to reduce the rate of respiration, microbial activity and refrigeration load. Pre-cooling can be done with chilled water, ice or cool air (forced air cooling), whereby the produce is cooled to the half cooling temperature.StorageStorage at low temperatures has been an effective mean of extending the shelf-life of fresh fruits and vegetables. It also enables orderly marketing and distribution of produce in time of peak production. Temperature requirements for different produce may vary depending on variety, location, stage of maturity and other factors. It is important to note that cool storage is a tool used to maintain quality but not to improve it.TransportationProper handling of the produce during transportation is essential to reduce losses to a minimum and to maintain their quality from the farm to the packing house and from packing house to market. The used of refrigerated trucks to transport highly perishable and high value produce will maintain their quality over an extended duration. In non ventilated vans, temperature of the fruits or vegetables rises quickly, increasing respiration and decay.