Volatile aroma compounds and acids were recovered in a short time period from roasted and ground coffee by steaming in a continuous counter-current apparatus. It was found that the recovery of volatiles depended upon the temperature of coffee steamed rather than the residence time of the coffee in the equipment. The total acid recovered both in the aroma condensate and in the aqueous extract from the steamed coffee with 5 minutes residence time was almost the same as that in a non-steamed coffee control. The generation of excess acids during steaming could therefore be minimized by short steaming times, compared with the traditional method of steaming a static coffee bed in a percolation column.
As steam flow rate was increased to obtain more condensate, the amount of total organic volatile compounds recovered in the condensate did not increase proportionally. Recovery of sulfur-containing compounds, however, significantly increased with the increase of steam flow rate.
Organoleptic evaluation of the coffee to which steam aroma was added suggested that sulfur-containing compounds were a key facter in obtaining regular brewed coffee flavor in a cup of soluble coffee.
The flavor of the steamed coffee deteriorated rapidly upon discharge from the equipment to the atmosphere. By organoleptic evaluation, a significant deteriorated note was perceived in the extract prepared from steamed coffee after 30 minutes hold-up. Acid generation in the steamed coffee increased rapidly after 90 minutes hold-up.