question: Why does exposure to air make food go stale?
comment: Moisture evaporates out of the food when it's exposed to air for to long. Moisture is what makes the food squishy and easily chewable. If you put the food in the microwave and put a damper paper towel near it, this helps a lot
passages: This process subjects the surface of food to a "flame" of ionized gas molecules, such as helium or nitrogen. This causes micro-organisms to die off on the surface.
  
  Section::::Modern industrial techniques.:High-pressure food preservation.
   Irradiation can also alter the nutritional content and flavor of foods, much like cooking. The scale of these chemical changes is not unique. Cooking, smoking, salting, and other less novel techniques, cause the food to be altered so drastically that its original nature is almost unrecognizable, and must be called by a different name. Storage of food also causes dramatic chemical changes, ones that eventually lead to deterioration and spoilage.
  
  Section::::Impact.:Immediate effects.:Misconceptions.
   Refers to the process in which air is absorbed into the food item. It refers to the lightness of cakes and bread, as measured by the type of pores they contain, and the color and texture of some sauces which have incorporated air bubbles.
  
  In wine tasting, a variety of methods are used to aerate wine and bring out the aromas including swirl wine in the glass, use of a decanter to increase exposure to air, or a specialized wine aerator.
   Directly following the heat treatment, vegetables/fruits are quickly chilled by cold water. A common alternative to cooling with cold water is cooling with cold air. This method of cooling prevents the leaching of water-soluble nutrients; however, the air causes evaporation and lowers the mass of the vegetable—a monetary disadvantage for industry.
  
  Emerging technologies include ohmic, infrared, microwave, and radio frequency blanching.
  
  Section::::Time and temperature.
   Steam blanching systems inject hot air (~100 °C) onto food as it passes through the blanching system on a conveyor belt. This method greatly reduces the leaching of water-soluble compounds from the product and is the preferred technique for smaller foods and those with cut surfaces. Steam blanching is more energy efficient, and the ability for quick heating allows for shorter processing times. This reduced heat exposure preserves color, flavor, and overall quality of the food; however, evaporation may occur leading to lower masses and product yields.
   Aging (food)
  
  Aging (American English) or ageing (British English), in the context of food or beverages, is the leaving of a product over an extended period of time (often months or years) to aid in improving the flavor of the product. Aging can be done under a number of conditions, and for a number of reasons:
  
  Section::::Drying.
   Various food preservation and packaging techniques are used to extend a food's shelf life. Decreasing the amount of available water in a product, increasing its acidity, or irradiating or otherwise sterilizing the food and then sealing it in an air-tight container are all ways of depriving bacteria of suitable conditions in which to thrive. All of these approaches can all extend a food's shelf life without unacceptably changing its taste or texture.
   Harvested foods decompose from the moment they are harvested due to attacks from enzymes, oxidation and microorganisms. These include bacteria, mold, yeast, moisture, temperature and chemical reaction. 
  
  Section::::Reasons.:Bacteria.
  
  Bacteria are responsible for the spoilage of food. When bacteria breaks down the food, acids and other waste products are created in the process. While the bacteria itself may or may not be harmful, the waste products may be unpleasant to taste or may even be harmful to one's health.
   Once opened for consumption, the product is immediately exposed to atmospheric oxygen and floating dust particles containing bacteria and mold spores, and all protections from the preservation process are immediately lost. At room temperature, mold and bacteria growth resumes almost immediately, and warmer temperatures can lead to an explosion of growth that rapidly degrades the food product. This organism growth can result in the accumulation of poisonous bacterial substances in the food product such as botulin, that lead to food poisoning, sickness, or death.
   During contact with the food, molecules can migrate from the food contact material to the food, for example via blooming. Because of this, in many countries regulations are made to ensure food safety.
  
  Section::::Food safe symbol.
   Approximately 500,000 tons of food items are irradiated per year worldwide in over 40 countries. These are mainly spices and condiments, with an increasing segment of fresh fruit irradiated for fruit fly quarantine.
  
  Section::::Modern industrial techniques.:Pulsed electric field electroporation.
   Drying of foods by leaving them in a low-humidity environment has been used as a food preservation technique for millennia. Air-dried meat such as jerky may have been some of the first preserved foods ever eaten by man. Drying also concentrates flavors in foods by removing water from them.
  
  Section::::Fermentation.
  
  Foods may be aged to allow fermentation to occur, such as in the making of alcoholic beverages, in cheesemaking, in pickling, such as kimchi, and in meat or fish products such as fermented sausage or surströmming.
  
  Section::::Culturing.
   Burial of food can preserve it due to a variety of factors: lack of light, lack of oxygen, cool temperatures, pH level, or desiccants in the soil. Burial may be combined with other methods such as salting or fermentation. Most foods can be preserved in soil that is very dry and salty (thus a desiccant) such as sand, or soil that is frozen.
   The earliest form of curing was dehydration or drying, used as early as 12,000 BC. Smoking and salting techniques improve on the drying process and add antimicrobial agents that aid in preservation. Smoke deposits a number of pyrolysis products onto the food, including the phenols syringol, guaiacol and catechol. Salt accelerates the drying process using osmosis and also inhibits the growth of several common strains of bacteria. More recently nitrites have been used to cure meat, contributing a characteristic pink colour.
  
  Section::::Traditional techniques.:Cooling.
   Section::::Traditional techniques.:Jellying.
   After use, organic matter that is still in the food packaging needs to be separated from the packaging. This may also require rinsing of the food packaging.
   Changing the Way – and what- we eat. Why is it hard to resist certain foods? is an interview by Lisa Meyers for NBC Nightly News with Brian Williams, where Civille gave details about how the consumer demands are forcing food companies to change the way they engineer food and how food panelists using descriptive analysis help to decode what the consumer really wants.
  
  Section::::Books.
   Section::::Uses.
  
  Blanching is a process used in the home kitchen as well as used as a pre-treatment in the food industry. In both cases, its main purpose is to inactivate enzymes that cause browning as well as textural changes and off-flavors. Enzymes that cause deterioration in fruits and vegetables include lipoxygenase, polyphenoloxidase, polygalacturonase, and chlorophyllase. Catalase and peroxidase are commonly used to determine blanching success, since they are the most thermal-resistant enzymes of concern. These enzymes are responsible for the loss of flavor, color, texture and nutritional qualities during product storage.
   Refrigerate after opening
  
  The term refrigerate after opening is an instruction on commercial preserved food products to cool the container after it has been opened and the contents exposed to open air.
  
  Moist foods are commonly preserved using canning and vacuum sealing to kill off any bacteria and molds, and to prevent further growth by removing oxygen. Dry-product containers are often preserved with heating and filling the empty container spaces with an inert nonreactive gas such as nitrogen.
   Section::::Formation.:Dehydration.
  
  Drying (dehydrating) is one of the oldest and easiest methods of food preservation. Dehydration is the process of removing water or moisture from a food product by heating at right temperature as well as containing air movement and dry air to absorb and carry the released moisture away. Reducing the moisture content of food prevents the growth of microorganisms such as bacteria, yeast and molds and slows down enzymatic reactions that take place within food. The combination of these events helps to prevent spoilage in dried food.
   Section::::Concerns.
   Blanching preserves the flavors found in fruits and vegetables by inactivating enzymes responsible for off-flavor development. The most common enzyme responsible for off-flavors is lipoxygenase (LOX) and is found in several vegetables.
  
  The blanching process expels air trapped inside plant tissues, which is a vital step before canning. Blanching prevents the expansion of air during processing, which reduces strain on the containers and the risk of cans having faulty seams. Moreover, removing gas from foods like pears results in better texture and reduces oxidation of the product. Also, the intercellular gases removed results in better color retention.
   Because of the non-reactive properties of inert gases they are often useful to prevent undesirable chemical reactions from taking place. Food is packed in inert gas to remove oxygen gas. This prevents bacteria from growing. It also prevents chemical oxidation by oxygen in normal air. An example is the rancidification (caused by oxidation) of edible oils. In food packaging, inert gases are used as a passive preservative, in contrast to active preservatives like sodium benzoate (an antimicrobial) or BHT (an antioxidant).
   A limitation to hot water blanching is the leaching of water-soluble nutrients and the degradation of thermal sensitive compounds. Vitamins, minerals, and other water-soluble compounds, such as proteins, sugars, and flavor compounds, diffuse out of the food and into the water, lowering the overall quality of the food. The degree to which compounds diffuse out of food depends on the food's composition and characteristics, the water to food ratio, the blanching temperature, and other variables. Ascorbic acid, thiamin, and many aromatic compounds are heat-sensitive.
   Section::::Nucleic acid denaturation.:Denaturation due to chemical agents.:Denaturation due to air.
  