question: Why does chewing gum become unchewable after a while?
comment: Chewing gum uses a food-safe polymer (a substance like plastic or rubber) as a base. When pure, that polymer is actually pretty stiff and flavorless. The gum companies add sweeterners, flavors, and softeners to the gum to make it nice and chewable. The chewing eventually pushes all those added ingredients out of the gum base, and it reverts to the original stiffness.
passages: "Does Your Chewing Gum..." has been a popular song on the Dr. Demento Show, appearing 54 times between the show's premiere and 2006 and selected for the "Dr. Demento 20th Anniversary Collection" double CD.
  
  In Ken Kesey's novel "One Flew Over the Cuckoo's Nest", the character Randle Patrick McMurphy also sings a few lines of this song when he realizes the Chief is storing used gum under his bed.
   Chewing gum is rather shelf stable because of its non-reactive nature and low moisture content. The water activity of chewing gum ranges from 0.40 to 0.65. The moisture content of chewing gum ranges from three to six percent. In fact, chewing gum retains its quality for so long that, in most countries, it is not required by law to be labeled with an expiration date. If chewing gum remains in a stable environment, over time the gum may become brittle or lose some of its flavor, but it will never be unsafe to eat. If chewing gum is exposed to moisture, over time water migration may occur, making the gum soggy. In lollipops with a gum center, water migration can lead to the end of the product's shelf life, causing the exterior hard candy shell to soften and the interior gum center to harden.
   It was referenced on "Talkin' 'Bout Your Generation". It was alluded to in the lyrics of "Ahab the Arab" by Ray Stevens, and the Buchanan and Goodman 1961 novelty number "Berlin Top Ten".
  
  It has made an appearances on children's television shows, such as "Sharon, Lois, & Bram's Elephant Show", "Kidsongs" and "Barney & Friends". The song "Does The Spearmint..." appears in one episode of HBO's series "Boardwalk Empire".
  
  Bruce Springsteen has described the song as having been one of his favorites as a child.
   The song is a cover version of "Does the Spearmint Lose Its Flavor on the Bedpost Overnight?" written by Billy Rose, Ernest Breuer, and Marty Bloom and first released in 1924 by The Happiness Boys (Ernie Hare and Billy Jones), and later a hit for Lulu Belle and Scotty and The Two Gilberts. The song is humorous in content, the verses each describing a dramatic or urgent scenario leading up to the asking of the titular question.
   Table 3: Gum Base Ingredients Approved for Use by the U.S. Food and Drug Administration (2016)
  
  Section::::Manufacturing process.
   The title and lyrics of the Donegan version were changed in the UK because "Spearmint" is a registered trademark there, and the BBC would not play songs that mentioned trademarks. Donegan's version of the song was recorded live at the New Theatre Oxford in December 1958 and was released both as a single and as a track on the album "King of Skiffle". An extended version with more banter was released on the live album "The Last Tour".
  
  Section::::Recordings.
   Does Your Chewing Gum Lose Its Flavour (On the Bedpost Overnight?)
  
  "Does Your Chewing Gum Lose Its Flavour (On the Bedpost Overnight?)" is a novelty song by Lonnie Donegan. Released as a single in 1959, it entered the UK Singles Chart on 6 February 1959 and peaked at number 3. It was also Donegan's greatest chart success in the United States, reaching number five on the "Billboard" Hot 100 chart in 1961.
   Since Donegan's version was released, it has appeared as a Smarties jingle, a performance on "The Muppet Show", and re-worked into Czech by Jiří Grossmann. Additional versions of the song were recorded by The Irish Rovers and Homer & Jethro. In 2010, Donegan's version was used as the background song for a satellite TV advertisement for Savlon antiseptic cream. It has also been recorded by Eric Nagler (on his 1982 children's album "Fiddle Up a Tune"); Ray Stevens covers the song as part of his 9-CD, 108 song box set "The Encyclopedia of Recorded Comedy Music" (2012).
  
  Section::::Popularity.
   Section::::Health effects.:Dental health.
   Studies have shown that gum flavor is perceived better in the presence of sweetener. Companies have started to create chemical systems in gum so that the sweetener and flavor release together in a controlled manner during chewing.
  
  Section::::Physical and chemical characteristics.:Cooling sensation.
   Section::::Physical and chemical characteristics.
  
  The physical and chemical properties of chewing gum impact all aspects of this product, from manufacturing to sensory perception during mastication.
  
  Section::::Physical and chemical characteristics.:Chewiness.
   Section::::Controversies.:Choking and excretion of swallowed gum.
  
  Various myths hold that swallowed gum will remain in a human's stomach for up to seven years, as it is not digestible. According to several medical opinions, there seems to be little truth behind the tale. In most cases, swallowed gum will pass through the system as quickly as any other food.
   Flavor delivery is extended throughout the mastication process by timed release of different flavor components due to the physical-chemical properties of many of chewing gum's ingredients. Entropy is a key player in the process of flavor delivery; because some gum components are more soluble in saliva than gum base and because over time flavor components desire to increase their entropy by becoming dispersed in the less ordered system of the mouth than in the more ordered system of the gum bolus, flavor delivery occurs. During the first three to four minutes of the chew, bulking agents such as sugar or sorbitol and maltitol have the highest solubility and, therefore, are chewed out first. As these components dissolve in the consumers’ saliva and slide down the esophagus, they are no longer retained in the gum base or perceived by the chewer. During the next phase of the chew in the four to six minute range, intense sweeteners and some acids are dissolved and chewed out. These components last slightly longer than the bulking agents because they have a slightly lower solubility. Next, encapsulated flavors are released during either 10-15 minute into the chew or after 30–45 minutes. Encapsulated flavors remain incorporated in the gum base longer because the molecules that they are encapsulated in are more easily held within the gum matrix. Finally, during the last phase of the chew, softeners such as corn syrup and glycerin and other textural modifiers are dissolved, resulting in a firming up of the gum and the end of the chew.
   Section::::Physical and chemical characteristics.:Stickiness.
   Section::::Controversies.
  
  Section::::Controversies.:Classification as food.
   Chewing gum is not water-soluble and unlike other confectionery is not fully consumed. There has been much effort at public education and investment aimed at encouraging responsible disposal. Despite this it is commonly found stuck underneath benches, tables, handrails and escalators. It is extremely difficult and expensive to remove once "walked in" and dried. Gum bonds strongly to asphalt and rubber shoe soles because they are all made from polymeric hydrocarbons. It also bonds strongly with concrete paving. Removal is generally achieved by steam jet and scraper but the process is slow and labour-intensive.
   Section::::Controversies.:Possible carcinogens.
   Section::::Manufacturing process.:Quality and safety.
   The polymers that make up the main component of chewing gum base are hydrophobic. This property is essential because it allows for retention of physical properties throughout the mastication process. Because the polymers of gum repel water, the water-based saliva system in a consumer's mouth will dissolve the sugars and flavorings in chewing gum, but not the gum base itself. This allows for gum to be chewed for a long period of time without breaking down in the mouth like conventional foods. Chewing gum can be classified as a product containing a liquid phase and a crystalline phase, providing gum with its characteristic balance of plastic and elastic properties.
   Section::::Physical and chemical characteristics.:Bubble-blowing capability.
   Adults have choked to death on chewing gum in rare cases. A 2012 report describes a 42-year-old woman who fell on the stairs while chewing gum. Due to the impact, the gum fell into the pharynx and was inhaled into the larynx, causing complete blockage and resulting in the woman's death by asphyxiation.
  
  Section::::Controversies.:Environmental effects.
   In modern chewing gum, if natural rubber such as chicle is used, it must pass several purity and cleanliness tests. However, most modern types of chewing gum use synthetic gum based materials. These materials allow for longer lasting flavor, a better texture, and a reduction in tackiness.
  
  Section::::History.
   Various teams of researchers have developed gum that is less adhesive and degrades within days or weeks. One example, Rev7 Gum, was briefly for sale from 2010 to 2012.
  
  Section::::Controversies.:Bans.
  
  Many schools do not allow chewing gum because students often dispose of it inappropriately (leaving it under desks and chairs, behind vending machines, etc.). The chewing may also pose a distraction to class, and the gum might carry diseases or bacteria from other students.
   Section::::Ingredient composition.
  
  Gum base composition is considered proprietary information known by select individuals within each gum-manufacturing company. Information about the other components of chewing gum are more accessible to the public and they are listed in Table 2.
  
  Table 2: Common Ingredients in the Formulation of Modern Chewing Gum
  
  Section::::Ingredient composition.:Gum base.
   Bazooka Joe gum was lampooned on "30 Rock", with Alec Baldwin's character telling a fictional story of the founder inheriting a "useless pink rock quarry" and turning it into gum by baking it. Later, a "softer version of their gum was used to make armor-piercing bullets." A fictional advertisement for the gum, starring Stacy Keach, encouraged viewers to chew Bazooka Joe gum "because life is hard," and "it's like chewing a mountain that someone shot a freeze ray into." 
  