Methylene chloride, also known as dichloromethane, is a solvent that, compared to water, can do a better job at dissolving certain substances such as grease, paint and caffeine. The so-called non polar solvent is mass-produced. It’s used by the fracking and plastic industry and in the production of HFC-32, a widely used replacement for CFCs that wreck the ozone, But there’s a catch. Once considered too short-lived as a molecule to act as a catalyst to break down ozone, dichloromethane, according to atmospheric model simulations, is causing damage that is not only negligible but becoming increasingly significant.
Then there’s the fact that IARC also considers it a probable human carcinogen, a classification based on several cohort studies of occupational exposure to the solvent’s vapors.
In the 1970s, dichloromethane was detected as a residual compound in decaffeinated coffee and tea. The levels ranged from < 0.05 to 4.04 mg/kg(ppm) in coffee, and < 0.05 to 15.9 mg/kg in tea. Because of concern over residues, most producers no longer use dichloromethane. Some people argue that no evidence links low levels of consumption to the kind of elevated risk for cancer experienced by workers who are exposed to much higher concentrations. But without implementing precautions, dichloromethane remains part of a much larger soup of invasive and potentially dangerous compounds.
Besides, there is a much more clever and innocuous method of extracting caffeine known as the Swiss Water Method.
First green (unroasted) coffee beans are soaked in hot water. This not only extracts a lot of caffeine but also aromatic and flavorful oils, and carbohydrates. But the Swiss method uses the problem as part of the solution, pun-intended! After soaking, the aqueous-solution from the first extraction is passed through a charcoal filter to remove caffeine. The charcoal is made in some countries from the discarded shells of coconuts. The caffeine molecules get trapped in the filter while its more desirable compounds, for the most part, pass through and stay in solution, a mixture known as “green coffee extract”. All other green beans that have to be decaffeinated are then soaked, not in hot water again, but in the green coffee extract. Because the solution is already saturated with the compounds that should remain in the coffee beans, for every non-caffeine molecule that leaves the beans, there is one that returns at the same rate, with the net result that the beans keep their flavor. But since the charcoal had removed the caffeine, the solution is not saturated with caffeine and these new beans still lose their caffeine to the extract. The extract is then passed through the filter again to remove the newly dissolved caffeine, and the process is repeated with yet another batch of beans to be decaffeinated.
Given all this, I was surprised to see that Costco’s Kirkland brand of decaffeinated coffee still uses methylene chloride. I promptly wrote to Costco. Oddly, they passed the complaint to the specific warehouse we shop at, which of course is not responsible for selecting the method of extraction. Perhaps coincidentally, and ever since my letter, I have not been able to see the product on their shelves. Another coincidence is that the product is currently unavailable at Amazon. Furthermore, the Costco website itself only offers an organic brand that uses the Swiss Water Method!
At the Canadian grocery chain, Loblaws, their name brand of decaffeinated coffee advertises the Swiss Water Method on its label, but their no-name brand does not specify. I called them yesterday, and I am happy to report that it too does not rely on methylene chloride. Its caffeine is extracted exactly the way its more expensive counterpart does it.
A friend asked me, “Please forgive me for asking but…what’s the point of decaf coffee? “. My response: I mix it with real coffee so I could drink 6 cups a day instead of 3!
The increasing threat to stratospheric ozone from dichloromethane. Nature Communications, DOI: 10.1038/ncomms15962