Caffeine was isolated from the coffee samples and measured by gas chromatography. Every serving but one - instant decaffeinated Folgers Coffee Crystals - contained caffeine, ranging from 8.6 milligrams to 13.9 milligrams. In comparison, an 8-ounce cup of drip-brewed coffee typically contains 85 milligrams of caffeine. In the study's second phase, scientists analyzed 12 samples of Starbucks decaffeinated espresso and brewed decaffeinated coffee taken from a single store.