The use of large, pressure-locked stainless steel or concrete tanks (called autovinificators) during the FERMENTATION of PORT. The naturally produced gases create enough pressure to force open the locks, pumping the juice up and over the CAP (seed, skins, stems, etc.) and thereby extracting TANNINS, color, and full fruit flavors. This technique replaces the traditional method of using long poles to push the cap down into the juice.