question: Why does food (bread, chips, etc.) go stale (much faster) when exposed to outside air for long enough but not from the air already inside the container/bag the food is stored in?
comment: The air inside has a finite amount of humidity. Whether pulling moisture from the food or providing it, the interaction is pretty short-lived. When left open, the air is relatively endless, and with it the ability to pull or provide moisture.
passages: Dust-laden gas or air enters the baghouse through hoppers and is directed into the baghouse compartment. The gas is drawn through the bags, either on the inside or the outside depending on cleaning method, and a layer of dust accumulates on the filter media surface until air can no longer move through it. When a sufficient pressure drop (ΔP) occurs, the cleaning process begins. Cleaning can take place while the baghouse is online (filtering) or is offline (in isolation). When the compartment is clean, normal filtering resumes.
   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.
   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).
   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.
   Sous vide, French for "under vacuum", implies that food should be sealed in a plastic bag with all the air removed. An alternative method is to place the food in an open-sided plastic bag and partially submerge the bag into the water, forcing out the air. This method involves clipping the open side of the bag to the side of the pot to keep water from leaking into the opening. The goal is to have the food completely in contact with the hot water to assure even cooking while reducing off-flavors from oxidation.
   Section::::Aseptic packaging.
  
  BiB is also used extensively in the packaging of processed fruit and dairy products in aseptic processes. Using aseptic packaging equipment, products can be packed in aseptic packaging. Pasteurised or UHT treated products packed into this format can be "shelf stable", requiring no refrigeration. Some products can have a shelf life of up to 2 years, depending on the type of bag that is used.
   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.
   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.
   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.
   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.
   BULLET::::- Barrier protection – A barrier to oxygen, water vapor, dust, etc., is often required. Permeation is a critical factor in design. Some packages contain desiccants or oxygen absorbers to help extend shelf life. Modified atmospheres or controlled atmospheres are also maintained in some food packages. Keeping the contents clean, fresh, sterile and safe for the duration of the intended shelf life is a primary function. A barrier is also implemented in cases where segregation of two materials prior to end use is required, as in the case of special paints, glues, medical fluids, etc.
   The perhaps best example is studies of the amount of oxygen in food packages. Oxygen is naturally present in most food and food packages as it is a major component in air. However, oxygen is also one of the great causes or needs for aging of biological substances, due to its source for increase of chemical and microbiological activity. Today, methods like [Modified atmosphere] (MAP) and [Controlled atmosphere] packaging (CAP) are implemented to reduce and control the oxygen content in food packages to prolong [shelf life] and ensure safe food. To assure the effectiveness of these methods it is important to regularly measure the concentration of oxygen (and other gases) inside these packages. GASMAS provides the possibility of doing this non-intrusively, without destroying any food or packages. The two main advantages of measuring the gas-composition in packages without perforation is that no food is wasted in the controlling process and that the same package can be controlled repeatedly during an extended time period to monitor any time-dependence of the gas composition. The studies can be used to guarantee the tightness of packages but also to study food deterioration processes.
   Solvents are a major source of contamination in chemical reactions. Although traditional drying techniques involve distillation from an aggressive desiccant, molecular sieves are far superior. 
   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.
   Packaging and package labeling have several objectives
  
  BULLET::::- Physical protection - The food enclosed in the package may require protection from, among , shock, vibration, compression, temperature, bacteria, etc.
  
  BULLET::::- Barrier protection - A barrier from oxygen, water vapor, dust, etc., is often required. Permeation is a critical factor in design. Some packages contain desiccants or oxygen absorbers to help extend shelf life. Modified atmospheres or controlled atmospheres are also maintained in some food packages. Keeping the contents clean, fresh, and safe for the intended shelf life is a primary function.
   Graham experimentally proved the dependency of gas diffusion on molecular weight, which is now known as Graham's law.
  
  Section::::History.:Richard Barrer (1910–1996).
  
  Barrer developed the modern Barrer measurement technique, and first used scientific methods for measuring permeation rates.
  
  Section::::Permeation in everyday life.
  
  BULLET::::- Packaging: The permeability of the package (materials, seals, closures, etc.) needs to be matched with the sensitivity of the package contents and the specified shelf life. Some packages must have nearly hermetic seals while others can (and sometimes must) be selectively permeable. Knowledge about the exact permeation rates is therefore essential.
   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.
   BULLET::::- Flow rate of air: This is in part related to the concentration points above. If "fresh" air (i.e., air which is neither already saturated with the substance nor with other substances) is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with time, thus encouraging faster evaporation. This is the result of the boundary layer at the evaporation surface decreasing with flow velocity, decreasing the diffusion distance in the stagnant layer.
  
  BULLET::::- The amount of minerals dissolved in the liquid
   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.
   The most common management practice for grains and legumes is the use of aeration systems. Air is pushed through the storage bins at low flow rates, which removes excess moisture and heat. Regulation of air flow allows the moisture content in harvested products to remain at a constant level and decreases the temperature within the bins. Temperature levels can decrease enough so insects and mites are dormant, which reduces rapid growth of the pathogen.
   Secondly there a "diffusion" process. The air arriving in the alveoli has a higher concentration of oxygen than the “stale” air in the alveoli. The increase in oxygen concentration creates a concentration gradient for oxygen between the air in the alveoli and the blood in the capillaries that surround the alveoli. Oxygen then moves by diffusion, down the concentration gradient, into the blood. The other consequence of the air arriving in alveoli is that the concentration of carbon dioxide in the alveoli decreases. This creates a concentration gradient for carbon dioxide to diffuse from the blood into the alveoli, as fresh air has a very low concentration of carbon dioxide compared to the blood in the body.
   Pre-made filters have two sides. One with loose holes, and the other with tight holes. Flow goes from the side with loose holes to the side with the tight holes, with the intent that large particles get stuck in the large holes while leaving enough room around the particles and filter medium for smaller particles to go through and get stuck in tighter holes.
  
  Sheets are sold in nominal ratings, and typically 90% of particles larger than the nominal rating are caught by the sheet.
  
  BULLET::::- Kieselguhr filters
   Cooling the food product to a temperature just above freezing in a refrigerator is generally required to slow the growth of these organisms. This cooling can permit foods to remain safely edible for up to two weeks after opening.
  
  Simply loosening the lid of a vacuum-packed food product to break the seal is enough to permit the bacteria and mold growth to resume. The amount of air inhaled into the container when the seal is broken is small, but sufficient to permit slow growth of contaminating and decomposing organisms.
   Carbon dioxide concentrations in closed or confined rooms can increase to 1,000 ppm within 45 minutes of enclosure. For example, in a sized office, atmospheric carbon dioxide increased from 500 ppm to over 1,000 ppm within 45 minutes of ventilation cessation and closure of windows and doors
  
  Section::::Common pollutants.:Ozone.
  
  Ozone is produced by ultraviolet light from the Sun hitting the Earth's atmosphere (especially in the ozone layer), lightning, certain high-voltage electric devices (such as air ionizers), and as a by-product of other types of pollution.
   Mix well or shake the bag. Empty the bag into top of container and close the lid. It must be able to be sealed and not let air enter or escape. Only the top vent should allow a controlled flow of steam to escape. Too much and most of the beneficial heat will escape and too little and the steam turns to streams of water in the inside and drops the internal temperature which in turn lowers the rate of decomposition.
  
  Section::::How it works.
  
presuppositions: Food should go stale from the air already inside the container/bag the food is stored in.
corrections: Air inside a container has a finite amount of humidity, compared to open air which can pull as much moisture as it wants.
raw_presuppositions: Food should go stale from the air already inside the container/bag the food is stored in. Food should go stale from the air already inside the container/bag the food is stored in.
raw_corrections: Air inside a container has a finite amount of humidity, compared to open air which can pull as much moisture as it wants. Air inside a container has a finite amount of humidity, compared to open air which can pull as much moisture as it wants.