autovinification, method of vinification designed to extract maximum colour from red grapes and used primarily in the production of red port. Autovinification, a process involving automatic pumping over, was developed in algeria in the 1960s, where it was known as the Ducellier system. Faced with a shortage of labour in the 1960s, port producers were forced to abandon the traditional practice of treading grapes by foot in lagares. Many isolated quintas had no electricity and so shippers built central wineries. The power supply was erratic and too weak for sophisticated pumps or presses so the shippers installed autovinification tanks in order to extract sufficient colour and tannins in the short fermentation period prior to fortification. Autovinification is a self-perpetuating process induced by the build-up of pressure; no external power source is needed.
Crushed and partially destemmed grapes are pumped into specially constructed autovinification vats (see diagram overleaf) which are filled to within about 75 cm (29 in) of the top. The vat is closed and the autovinification unit (a) is screwed into place. As the fermentation begins, carbon dioxide is given off and pressure builds up inside the vat. This drives the fermenting must up an escape valve (b) which spills out into an open reservoir (1) on top of the vat. Eventually the pressure will also force the water out of a second valve (c) into a smaller, separate reservoir (2). When the water has been expelled, the carbon dioxide that has built up in the vat escapes with explosive force through valve (c). The fermenting must in reservoir (1) falls back into the vat down the central autovinification unit (a), spraying the floating cap of grape skins, so extracting colour and tannin. At the same moment, the water in reservoir (2) returns to valve (c), again sealing in the carbon dioxide, and the process repeats itself. The cycle continues until the winemaker judges that sufficient grape sugar has been fermented to alcohol, and sufficient colour has been extracted, at which time the wine is run off and fortified just as described in port, winemaking.
At the start of fermentation, when a small amount of carbon dioxide is given off, the autovinification cycle is slow. But when the fermentation is in full swing, the pressure build-up is such that the cycle takes only 10–15 minutes to complete.
Originally autovinification vats were built from concrete and lined with resin-painted concrete. However, significant modifications have accompanied improvements in both winemaking technology and the power supply to the douro valley, where port is produced. Modern autovinification tanks are made from stainless steel and are equipped with refrigeration units to prevent the must from overheating. Some shippers have resorted to traditional pumping over, or remontage, although this generally provides insufficient extraction for better-quality port. Other shippers have successfully combined pumping over with autovinification, thereby giving the winemaker greater control over port fermentation than ever before, although lagares are preferred by many for top-quality ports.
