Though it is incorrectly translated as Istrian soup, this unusual combination of ingredients does not have much in common with the traditional concept of what constitutes a classic soup. The dish is prepared in a clay jug called bukaleta and combines spices, olive oil, and warmed red wine, preferably the local teran variety.

Supa is completed with the addition of grilled slices of bread that are left to soak in the flavorful base. When served, the wine is slowly sipped, while the bread is usually eaten with a spoon. Once a popular dish that was mainly used as a way to warm up during winter, istarska supa is nowadays considered one of the authentic delicacies of the area.

The word supa in the name stems from the verb supati, referring to the practice of dunking the bread in the jug.