Decaffeinated coffee, or "decaf," is similar in taste and appearance to regular coffee but contains very little caffeine. There is no evidence to suggest that drinking decaf is bad for a person's health, and it may even share some of the health benefits of regular coffee.
According to a 2017 research review, decaf coffee is similar in composition to regular coffee but contains little or no caffeine. To remove the caffeine, manufacturers soak or steam unroasted coffee beans using a combination of water and other chemicals, such as: activated charcoal, supercritical carbon dioxide, methylene chloride and ethyl acetate. Manufacturers use water because caffeine is a water-soluble substance. However, using water by itself may remove other compounds, such as proteins and sugar, from the coffee beans. Using additional chemicals speeds up the decaffeination process, which minimizes the loss of noncaffeine compounds and helps preserve the distinct coffee flavor.
One 2-17 study reviewed 201 meta-analyses of observational research into coffee consumption. Its authors concluded that decaf coffee does not appear to have any harmful health effects. However, the use of methylene chloride in the decaffeination process has raised some concern among members of the coffee community as well as some consumers.
Inhaling even small amounts of methylene chloride — around 200 parts per million (ppm) in the air — can temporarily slow down the central nervous system and affect a person's attention and hand-eye coordination. Mild exposure can also lead to symptoms such as: headache, drowsiness, lightheadedness, irritability, coughing or wheezing
The FDA has approved the use of methylene chloride in the caffeine extraction process as long as the final product contains no more than 10 ppm, or 0.001%, of residual methylene chloride.
Despite its name, decaf coffee does still contain some caffeine.
According to the United States Department of Agriculture (USDA), a typical 8 ounce (oz) cup of decaf coffee contains 2mg of caffeine. However, the caffeine content can vary by brand, with some decaf coffees containing up to 15mg per 8 oz cup. According to the FDA, an 8 oz cup of regular coffee typically contains 80–100 mg of caffeine.
Green and black teas also contain more caffeine than decaf coffee. A regular 8 oz cup of green or black tea usually contains about 30-50mg of caffeine.
A growing body of scientific research suggests that coffee contains several compounds that are beneficial to human health. For example, a large 2017 review suggests that drinking coffee can lower a person's risk of developing certain cancers. However, much of the research looked at the health benefits of regular coffee, with few studies focusing on decaf coffee specifically. So, it is not clear whether the health benefits of regular coffee extend to decaf.
That said, the authors of the 2017 review did find a link between drinking decaf and a reduced risk all-cause mortality and death from cardiovascular causes. The researchers observed the greatest risk reduction in people who drank two to four cups per day.
Methylene chloride is also used in paint strippers and has been deemed responsible for the deaths associated with the use of these products. Ethyl acetate is used in nail polish. As an organic solvent, it is what makes the odor from nail polish so strong. Besides being extremely flame able, it is toxic when ingested or inhaled.
Avoid decaf coffee unless it is naturally decaffeinated using the Swiss water process. This process soaks the beans in carbon dioxide, removing 97% of the caffeine.
Source: June 18, 2019 NIH