South African wine has a history dating back to 1659 with Constantia, a vineyard near Cape Town, being considered one of the greatest wines in the world. Access to international markets has unleashed a burst of new energy and new investment. Production is concentrated around Cape Town, with major vineyard and production centres at Paarl, Stellenbosch and Worcester. There are about 60 appellations within the Wine of Origin (WO) system, which was implemented in 1973 with a hierarchy of designated production regions, districts and wards. WO wines must be made 100% from grapes from the designated area. "Single vineyard" wines must come from a defined area of less than 5 hectares. An "Estate Wine" can come from adjacent farms, as long as they are farmed together and wine is produced on site.