A while ago I bought a blend of decaffeinated natural Brazilian coffees from the Region of Sul de Minas (700 - 1100m above sea level). The supercritical CO2 process was used.
Food scientists have also turned to supercritical carbon dioxide as a means of decaffeination. Developed by Kurt Zosel, a scientist of the Max Planck Institute, it uses CO2, heated and pressurised above its critical point, to extract caffeine. In this process, green coffee beans are steamed and then added to a high pressure vessel. A mixture of water and carbon dioxide (CO2) is circulated through the vessel at 300 atm and 65 ºC (150°F). At this temperature and pressure CO2 is a supercritical fluid, with properties midway between a gas and a liquid. Caffeine dissolves into the CO2; compounds contributing to the flavour of the brewed coffee are largely insoluble in CO2 and remain in the bean. In a separate vessel, caffeine is scrubbed from the CO2 with additional water. The CO2 is then recirculated to the pressure vessel.
It was supposed to taste of malt, molasses, nuts and chocolate but when I opened the bag, the coffee smelled like petrol, and pretty agressively so. It smelled a little like caramel but the smell of petrol was just overwhelming. While brewing, especially during the bloom, the grounds smelled of tobacco. The coffee was pretty sour, tasted of tobacco, tar, and petrol. I tried adjusting the grind size but to no avail. I also tried waiting a week, two weeks, 4 weeks, 6 weeks and 8 weeks - the coffee smelled and tasted exactly the same.
Now keep in mind these beans were by no means roasted dark, it was a medium roast, definitely not roasted much beyond the first crack.
Are these tastes considered defects? How do these tastes end up in the coffee? Were the green beans bad, did it happen during the decaffeination or did the roasters screw up?
I have had many decaffeinated coffees so far but none tasted of tobacco and petrol - many just tasted like sour chocolate and a little hollow.