question: why tea stains my cup but not coffee?
comment: Tea contains tannins, or tannic acid, that leaves stains. Coffee doesn’t have tannins. Red wine would stain a ceramic mug for the same reason.
passages: Section::::Materials.
  
  Section::::Materials.:Porcelain.
  
  Porcelain allows for heat retention and crema preservation. However, porcelain cools down quickly due to air bubbles in the cup. Crema is the coffee foam at the top of a shot of espresso. Preserving it in cups allows for latte art to occur in milk based espresso drinks.
  
  Section::::Materials.:Ceramic.
   Tea contains small amounts of theobromine and slightly higher levels of theophylline than coffee. Preparation and many other factors have a significant impact on tea, and color is a very poor indicator of caffeine content. Teas like the pale Japanese green tea, "gyokuro", for example, contain far more caffeine than much darker teas like "lapsang souchong", which has very little.
  
  Section::::Products.:Beverages.:Soft drinks and energy drinks.
   Brewing with a paper filter produces clear, light-bodied coffee. While free of sediments, such coffee is lacking in some of coffee's oils and essences; they have been trapped in the paper filter. Metal filters do not remove these components.
   Section::::Brewing.:Filtration methods.
   A subtler issue is "which" solubles are dissolved – this depends on solubility of different substances at different temperatures, changes over the course of extraction (different substances are extracted during the first 1% of extraction than in the period from 19% extraction to 20% extraction), and is primarily affected by "temperature."
   Alternating voltage electrowetting may suppress coffee stains without the need to add surface-active materials. Reverse particle motion may also reduce the coffee-ring effect because of the capillary force near the contact line. The reversal takes place when the capillary force prevails over the outward coffee-ring flow by the geometric constraints.
  
  Section::::Determinants of size and pattern.
   Coffee ring effect
  
  In physics, a "coffee ring" is a pattern left by a puddle of particle-laden liquid after it evaporates. The phenomenon is named for the characteristic ring-like deposit along the perimeter of a spill of coffee. It is also commonly seen after spilling red wine. The mechanism behind the formation of these and similar rings is known as the coffee ring effect or in some instances, the coffee stain effect, or simply ring stain.
  
  Section::::Flow mechanism.
   The silicone of which most brands of cups are produced is naturally colorless and translucent. Several brands offer colored cups as well as, or instead of the colorless ones. Translucent cups lose their initial appearance faster than colored – they tend to get yellowish stains with use. The shade of a colored cup may change over time, though stains are often not as obvious as on colored cups. Stains on any color of cup can often be removed or at least lightened by soaking the cup in diluted hydrogen peroxide and/or leaving it out in the sun for a few hours.
   Originally, paper cups for hot drinks were glued together and made waterproof by dropping a small amount of clay in the bottom of the cup, and then spinning at high speed so that clay would travel up the walls of the cup, making the paper water-resistant. However, this resulted in drinks smelling and tasting of cardboard.
   Other methods of printing have been used for short runs such as offset printing, which can vary from anything from 10,000 to 100,000 cups. Offset printing inks have also been developed and although in the past these were solvent based, the latest soya-based inks have reduced the danger of cups smelling. The latest development is Direct-printing, which allows printing on very small quantities, typically from 1,000 cups, and is used by companies including Brendos ltd offering small quantities in short lead times. Rotogravure can also be used, but this is extremely expensive and is normally only utilised for items requiring extremely high quality printing like ice cream containers.
   BULLET::::- Caramel – This aroma descriptor is reminiscent of the odour and flavour produced when caramelizing sugar without burning it. Tasters should be cautioned not to use this attribute to describe a burning note.
   BULLET::::- Coffee sample trays – Traditionally coffee sample trays are set out on the coffee tasting table behind the cup being tasted. There will be a tray for the green coffee, a tray for the whole roasted coffee beans, and one for the fresh ground coffee; so that the coffee taster can inspect the color, and aroma of all three states that the coffee comes in. The coffee taster will run his/her finger through the coffee in the tray, then run his/her nose through the coffee in the tray.
   Section::::Brewing coffee.
  
  Coffee is brewed by first folding the paper filter into shape and placing it and the ground coffee into the neck of the flask. Hot water (93-96 °C/195-205 °F) is then poured through the coffee and filter, depositing brewed coffee into the flask.
  
  Section::::In popular culture.
  
  In the 1954 romance movie "Sabrina", a Chemex Coffeemaker can be seen in the corner of Linus's bar in his office. 
   Section::::Composition.:Lipids.
   Section::::Composition.:Volatile compounds.
   Jay Isais, Coffee Bean's senior director of coffee, oversees the quality of the blending and roasting of all the company's beans. A founding member of the Roasters' Guild, he joined Coffee Bean in 2000. He is one of approximately 400 licensed Q graders worldwide, passing an exam of sensory tests administered by the Specialty Coffee Association of America's CQI division.
  
  Section::::Products.:Teas.
   Section::::Aromas.
  
  Various descriptions are used to note coffee aroma.
  
  BULLET::::- Animal-like – This odour descriptor is somewhat reminiscent of the smell of animals. It is not a fragrant aroma like musk but has the characteristic odour of wet fur, sweat, leather, hides or urine. It is not necessarily considered as a negative attribute but is generally used to describe strong notes.
   Section::::Composition.:Nonvolatile chlorogenic acids.
   This is an optional process in which any silver skin that remains on the beans after hulling is removed in a polishing machine. This is done to improve the appearance of green coffee beans and eliminate a byproduct of roasting called chaff. It is described by some to be detrimental to the taste. By raising the temperature of the bean through friction which changes the chemical makeup of the bean.
  
  Section::::Milling.:Cleaning and sorting.
   Thermochromic paints use liquid crystals or leuco dye technology. After absorbing a certain amount of light or heat, the crystallic or molecular structure of the pigment reversibly changes in such a way that it absorbs and emits light at a different wavelength than at lower temperatures. Thermochromic paints are seen quite often as a coating on coffee mugs, whereby once hot coffee is poured into the mugs, the thermochromic paint absorbs the heat and becomes colored or transparent, therefore changing the appearance of the mug.
  
  Section::::Organic materials.:Leuco dyes.:Papers.
   The name is derived from the word "percolate" which means "to cause (a solvent) to pass through a permeable substance especially for extracting a soluble constituent". In the case of coffee-brewing the solvent is water, the permeable substance is the coffee grounds, and the soluble constituents are the chemical compounds that give coffee its color, taste, aroma, and stimulating properties.
   Some Romanian methods require that the sediments be swirled around until they cover the majority of the cup's inside surface. Other traditions, such as Turkish and Middle Eastern, do not require this swirling but do require that the cup be turned towards the querent in revealing the fortune. The coffee grounds are given time to dry against the cup before a reading begins.
   Chris Difford stated, "[t]he lyric was inspired by my picking up my notebook one day and seeing a coffee stain on it, which inspired the first line. It was a very vivid image for me and inspired this song of loss and regret." Difford also said that "lyrically it was attractive to [a country] kind of metre. The fact that Glenn put a soul melody to it shows the unique quality of our writing."
   Names for different types of cups vary regionally and may overlap. Any transparent cup, regardless of actual composition, is likely to be called a "glass"; therefore, while a cup made of paper is a "paper cup", a transparent one for drinking shots is called a "shot glass", instead.
  
  Section::::Types.:Cups for hot beverages.
  
  While in theory, most cups are well suited to hold drinkable liquids, hot drinks like tea are generally served in either insulated cups or porcelain teacups. 
  
  BULLET::::- Coffee cup
  
  BULLET::::- Mazagran
  
  BULLET::::- Mug
  
  BULLET::::- Teacup
  
  BULLET::::- Thermos
  
  BULLET::::- Travel mug
  
  Section::::Types.:Disposable cups.
   Finally having had enough of being bullied by the thug, Bean decides to get revenge by replacing the man's softener with a cup of black coffee from the vending machine. This works, as the man does not realise that he is pouring the coffee into the machine instead of his detergent. However, when the thug gets suspicious after sniffing the cup, Bean drinks the softener to make it look as if he is drinking coffee. Later, the thug blames the launderette's manager as his martial arts gear comes out of the machine, all severely stained from the coffee.
  