The prickly lettuce of Bergamo differs from the other varieties on the market for the particular whitening process the inner leaves are subject to. Sown only in open fields from the end of July, at the end of October each head gets tied up so that the inner leaves are not exposed to the light. A unique ripening process then begins. When the cold season comes, the small plants are moved to the ancient cellars of Città Alta where market gardeners, which have been handing down this technique since generations, unfold them in the darkness. In this way, the inner leaves ripen but do not acquire any color.