This study tested the hypothesis that differences in the processing of raw coffee beans can account for some of the variability in gastric effects of coffee drinking. Coffees were selected to represent several ways that green coffee beans are treated, ie, processing variables. These included instant and ground coffee processing, decaffeination method (ethyl acetate or methylene chloride extraction), instant coffee processing temperature (112 degrees F or 300 degrees F), and steam treatment. Lower esophageal sphincter pressure, acid secretion, and blood gastrin was measured in eight human subjects after they consumed each of the different coffees. Consumption of coffee was followed by a sustained decrease in lower esophageal sphincter pressure (P less than 0.05) except for three of the four coffees treated with ethyl acetate regardless of whether or not they contained caffeine. Caffeinated ground coffee stimulated more acid secretion that did decaf ground coffees (P less than 0.05), but not more than a steam-treated caffeinated coffee. Instant coffees did not differ in acid-stimulating ability. Ground caffeinated coffee resulted in higher blood gastrin levels than other ground coffees (P less than 0.05). Freeze-dried instant coffee also tended toward higher gastrin stimulation. It is concluded that some of the observed variability in gastric response to coffee consumption can be traced to differences in how green coffee beans are processed.