In the 1930’s, an approach to the treatment of coffee was discovered that helped to reduce the level of stomach irritants in coffee. It involved the treatment of raw coffee beans with water and saturated steam to remove unwanted components such as wax or carboxylic acids of 5-hydroxy-tryptamide from the bean. Since these low irritant coffees keep their full caffeine content, this approach has become an alternative for coffee drinkers with sensitive stomachs.
Several companies have developed different methods to steam raw coffee before roasting. Depending on the process parameters, the effect on the taste of the coffee varies. Usually the first step is to loosen the silver skins by a mild warm steam treatment and to remove them from the beans by applying a circulating airflow. Following this, the raw beans are steamed with different degrees of pressure, temperature and moisture levels, leading to a change in the coffee beans components, especially carbohydrates and proteins, which results in the reduction of acidity and the removal of other irritant components.
In the 1980’s, an almost similar process was developed to reduce unwanted taste components in robusta coffees, mainly by increasing the pressure in the vessel. This high pressure steaming makes it possible to use more robusta coffees in the blends.