question: How does coffee become decaffeinated? Is it healthy for you, or is the coffee equivalent of diet sodas?
comment: The method I'm aware of is that they basically wash the beans with liquid Co2, and make "Co2 coffee" with it until they have removed at least half the caffeine. I'm sure there are other methods, but this in particular wouldn't make it toxic or anything. Just weaker since it's been used already.
passages: In the case of decaffeinated coffee, eliminating caffeine can cause a sharp decline in the natural taste of the coffee bean. During the process of decaffeination, the largest coffee producers in the world use a variety of ways to remove caffeine from coffee, often by means of chemical manipulation and the use of potentially harmful chemical components, such as methylene chloride or ethyl acetate. One process that does not use solvents is the patented Swiss Water Process, which relies on soaking beans in a bath which is essentially brewed coffee from unroasted green beans. The caffeine permeates into the bath at a much higher rate than most of the flavor elements. While the process is certified organic, the water solubility of coffee flavor compounds assures that some of the coffee flavor is lost or changed by the bath. The process is more costly than solvent methods, and is performed commercially by only one plant in British Columbia, Canada. Therefore, only a small percentage of decaffeinated coffee available on the market uses this method.
   BULLET::::- Extraction by organic solvents: Certain organic solvents such as ethyl acetate present much less health and environmental hazard than chlorinated and aromatic organic solvents used formerly. Another method is to use triglyceride oils obtained from spent coffee grounds.
  
  "Decaffeinated" coffees do in fact contain caffeine in many cases – some commercially available decaffeinated coffee products contain considerable levels. One study found that decaffeinated coffee contained 10 mg of caffeine per cup, compared to approximately 85 mg of caffeine per cup for regular coffee.
  
  Section::::Chemistry.:Detection in body fluids.
   Decaffeination is the process of extracting caffeine from green coffee beans prior to roasting. The most common decaffeination process used in the United States is supercritical carbon dioxide (CO) extraction. In this process, moistened green coffee beans are contacted with large quantities of supercritical CO (CO maintained at a pressure of about 4,000 pounds force per square inch (28 MPa) and temperatures between ), which removes about 97% of the caffeine from the beans. The caffeine is then recovered from the CO, typically using an activated carbon adsorption system.
   A controlled study of ten samples of prepared decaffeinated coffee from coffee shops showed that some caffeine remained. Fourteen to twenty cups of such decaffeinated coffee would contain as much caffeine as one cup of regular coffee. The 473 ml (16 ounce) cups of coffee samples contained caffeine in the range of 8.6 mg to 13.9 mg. In another study of popular brands of decaf coffees, the caffeine content varied from 3 mg to 32 mg. A 237 ml (8 ounce) cup of regular coffee contains 95–200 mg of caffeine, and a 355 ml (12 ounce) serving of Coca-Cola contains 36 mg.
   Both of these studies tested the caffeine content of store-brewed coffee, suggesting that the caffeine may be residual from the normal coffee served rather than poorly decaffeinated coffee.
  
  Section::::Decaffito.
  
  As of 2009, progress toward growing coffee beans that do not contain caffeine was still continuing. The term "Decaffito" has been coined to describe this type of decaffeinated coffee, and trademarked in Brazil.
   Green coffee beans are soaked in a hot water/coffee solution to draw the caffeine to the surface of the beans. Next, the beans are transferred to another container and immersed in coffee oils that were obtained from spent coffee grounds and left to soak.
  
  After several hours of high temperatures, the triglycerides in the oils remove the caffeine, but not the flavor elements, from the beans. The beans are separated from the oils and dried. The caffeine is removed from the oils, which are reused to decaffeinate another batch of beans. This is a direct-contact method of decaffeination.
  
  Section::::Decaffeinated coffee.
   In the case of coffee, various methods can be used for decaffeination. These methods take place prior to roasting and may use organic solvents such as methylene dichloride or ethyl acetate, supercritical CO, or water to extract caffeine from the beans while leaving flavour precursors in as close to their original state as possible.
  
  Section::::Decaffeination processes for coffee.:Organic solvent processes.
  
  Section::::Decaffeination processes for coffee.:Organic solvent processes.:Direct method.
   A decaffeination process removes caffeine from coffee beans to lower their caffeine content. Four main methods are used to extract caffeine from coffee beans:
  
  BULLET::::- The so-called "Swiss" water method, so called from allegedly having been developed in Switzerland, where the beans are soaked in water;
  
  BULLET::::- the ethyl acetate method, where the beans are washed in a solution of water and ethyl acetate;
  
  BULLET::::- the carbon dioxide method, where either liquid or "supercritical" (between liquid and gas) carbon dioxide is applied to the beans at high pressure; or
   Decaffeination
  
  Decaffeination is the removal of caffeine from coffee beans, cocoa, tea leaves, and other caffeine-containing materials. While soft drinks which do not use caffeine as an ingredient are sometimes described as "decaffeinated", they are better termed "non-caffeinated" because decaffeinated implies that there was caffeine present at one point in time. Decaffeinated drinks contain typically 1–2% of the original caffeine content, and sometimes as much as 20%. Decaffeinated products are commonly termed decaf.
  
  Section::::History.
  
  Section::::History.:Coffee.
   Section::::Decaffeination processes for coffee.:Supercritical CO process.
  
  In this process, green coffee beans are steamed and then added to a high pressure vessel. A mixture of water and liquid CO is circulated through the vessel at 300 atm and 65 ºC (150°F). Caffeine dissolves into the CO; compounds contributing to the flavour of the brewed coffee are largely insoluble in CO and remain in the bean. In a separate vessel, caffeine is scrubbed from the CO with additional water. The CO is then recirculated to the pressure vessel.
  
  Section::::Decaffeination processes for coffee.:Swiss Water process.
   Most recently, food scientists have turned to supercritical carbon dioxide as a means of decaffeination. Developed by Kurt Zosel, a scientist of the Max Planck Institute, it uses CO, heated and pressurized above its critical point, to extract caffeine and could be useful going forward because it circumvents the use of other solvents and their possible effects entirely.
  
  Section::::Decaffeination processes for coffee.
   The prospect for Decaffito-type coffees was shown by the discovery of the naturally caffeine-free "Coffea charrieriana", reported in 2004. It has a deficient caffeine synthase gene, leading it to accumulate theobromine instead of converting it to caffeine. Either this trait could be bred into other coffee plants by crossing them with "C. charrieriana", or an equivalent effect could be achieved by knocking out the gene for caffeine synthase in normal coffee plants.
  
  Section::::Decaffeinated tea.
   In the direct organic solvent process, unroasted (green) beans are first steamed and then rinsed with a solvent (e.g. methylene dichloride or ethyl acetate). The solvent extracts the caffeine while leaving other constituents largely unaffected. The process is repeated from 8 to 12 times until the caffeine content meets the required standard (97% of caffeine removed according to the US standard, or 99.9% caffeine-free by mass per the EU standard). 
  
  Section::::Decaffeination processes for coffee.:Organic solvent processes.:Indirect method.
   Decaffeination of coffee seeds is done while the seeds are still green. Many methods can remove caffeine from coffee, but all involve either soaking the green seeds in hot water (often called the "Swiss water process") or steaming them, then using a solvent to dissolve caffeine-containing oils. Decaffeination is often done by processing companies, and the extracted caffeine is usually sold to the pharmaceutical industry.
  
  Section::::Processing.:Storage.
   Section::::Decaffeinated coffee.:Caffeine content of decaffeinated coffee.
   Another commonly used method is solvent extraction, typically using oil (extracted from roasted coffee) or ethyl acetate as a solvent. In this process, solvent is added to moistened green coffee beans to extract most of the caffeine from the beans. After the beans are removed from the solvent, they are steam-stripped to remove any residual solvent. The caffeine is then recovered from the solvent, and the solvent is re-used. The Swiss Water Process is also used for decaffeination. Decaffeinated coffee beans have a residual caffeine content of about 0.1% on a dry basis. Not all facilities have decaffeination operations, and decaffeinated green coffee beans are purchased by many facilities that produce decaffeinated coffee.
   Once the GCE is rich with caffeine it is then percolated through carbon absorbers which attract the caffeine molecule from the GCE while leaving other green coffee elements intact in the GCE. When the GCE is once again lean of caffeine it is then used to remove additional caffeine from the green coffee. This is a continuous batch process that takes 8–10 hours to meet the final residual decaffeinated target.
  
  Section::::Decaffeination processes for coffee.:Triglyceride process.
   BULLET::::- the dichloromethane method, where dichloromethane, a solvent, is used to dissolve the caffeine.
  
  Decaffeinated coffee grew in popularity over the last half of the 20th century, mainly due to health concerns that arose regarding the over-consumption of caffeine. Decaffeinated coffee, sometimes known as "decaf," may be drunk as regular brewed coffee, instant, espresso, or as a mix of regular caffeine beans and decaffeinated beans.
  
  Section::::Other.
  
  BULLET::::- Affogato
   Another process, known as the Swiss Water Method, uses solely water and osmosis to decaffeinate beans. The use of water as the solvent to decaffeinate coffee was originally pioneered in Switzerland in 1933 and developed as a commercially viable method of decaffeination by Coffex S.A. in 1980. In 1988, the Swiss Water Method was introduced by The Swiss Water Decaffeinated Coffee Company of Burnaby, British Columbia, Canada. Noted food engineer Torunn Atteraas Garin also developed a process to remove caffeine from coffee.
   Another variation of Roselius' method is the indirect organic solvent method. This is very similar to the process described above, only instead of treating the beans directly, water resulting from the soaking of beans is treated with solvents and the process goes on until equilibrium is reached without caffeine in the beans. This method was first mentioned in 1941, and people have made great efforts to make the process more "natural" and a true water-based process by finding ways to process the caffeine out of the water in ways that circumvents the use of organic solvents.
   Low caffeine coffee
  
  Low caffeine coffee is a term that is used by coffee producers to describe coffee that has not been subjected to a process of decaffeination, but is substantially lower in caffeine than average coffee. Samples of coffee vary widely in caffeine levels due to many factors, some well documented (such as genetics) and some not fully understood, such as the action of soil, water levels and sunlight. Low caffeine coffees are typically created by assaying caffeine levels of different bean lots and selecting the best flavor profile from the lots that are naturally lowest in caffeine.
  
  Section::::Decaffeination.
   The first commercially successful decaffeination process was invented by German merchant Ludwig Roselius and co-workers in 1903 and patented in 1906. In 1903, Ludwig accidentally stumbled upon this method when his freight of coffee beans was soaked in sea water and lost much of its caffeine without losing much taste. This original decaffeination process involved steaming coffee beans with various acids or bases, then using benzene as a solvent to remove the caffeine. Coffee decaffeinated this way was sold as Kaffee HAG after the company name "Kaffee Handels-Aktien-Gesellschaft" (Coffee Trading Company) in most of Europe, as "Café Sanka" in France and later as Sanka brand coffee in the US. Café HAG and Sanka are now worldwide brands of Kraft Foods. Because of health concerns regarding benzene (which is recognised today as a carcinogen), benzene is no longer used as a solvent commercially.
   In the indirect method, beans are first soaked in hot water for several hours, in essence making a strong pot of coffee. Then the beans are removed and either dichloromethane or ethyl acetate is used to extract the caffeine from the water. As in other methods, the caffeine can then be separated from the organic solvent by simple evaporation. The same water is recycled through this two-step process with new batches of beans. An equilibrium is reached after several cycles, wherein the water and the beans have a similar composition except for the caffeine. After this point, the caffeine is the only material removed from the beans, so no coffee strength or other flavorings are lost. Because water is used in the initial phase of this process, indirect method decaffeination is sometimes referred to as "water-processed".
   A small amount of chaff is produced during roasting from the skin left on the seed after processing. Chaff is usually removed from the seeds by air movement, though a small amount is added to dark roast coffees to soak up oils on the seeds.
  
  Section::::Processing.:Decaffeination.
   Certain processes during normal production might help to decrease the caffeine content directly, or simply lower the rate at which it is released throughout each infusion. Several instances in China where this is evident is in many cooked pu-erh teas, as well as more heavily fired Wuyi Mountain oolongs; commonly referred to as 'zhonghuo' (mid-fired) or 'zuhuo' (high-fired).
  
  A generally accepted statistic is that a cup of normal black (or red) tea contains 40–50 mg of caffeine, roughly half the content of a cup of coffee.
  