The Lagare is an open shallow concrete vat, perhaps one metre deep and several metres square. After the grapes are picked during the day, they are spread across the bottom of the Lagare until they reach a depth of about knee-height. Each Lagare contains a large drain connected directly to the fermentation vats and all are filled with the grapes every harvest day. Treading is taken very seriously as it is this process which lends Quinta de la Rosa wine a very special quality.
The local pickers, many of whom spent the day hauling the same grapes up and down the mountainside, bare footed and bare legged, clad in T-shirts and shorts, climb carefully into the open vat of freshly picked grapes. The individuals in each team link or place arms around each other's shoulders, thus, forming a continuous treading line. One designated individual quite loudly begins to call the treading rhythm, as he does so the left and then right leg of each of the individuals rises and falls in unison compressing the fruit with the bare soles of their feet.
The team continue relentlessly on for two full hours without a break. Once this first stage known as the 'Military' is completed, a further one hour of 'free' treading follows, this usually occurs at night, and often to the accompanied by music.
The end result (other than a number of purple workers) resembles nothing more than a port-filled stone tub. The naked human foot is actually ideal in that it applies just enough pressure to crush the grapes, but at the same time is soft enough to avoid shattering any of the grape seeds, releasing bitter flavours into the juice (a common flaw of mechanical presses).
While foot-treading is unusual, it is the fermentation process - or more accurately the practice of what might be called 'fermentus interruptus' - that makes port unique. This unnatural technique dates back nearly 300 years.
Though not unique to Quinta de la Rosa only a handful of properties in the Douro maintain this labour intensive tradition.