See 'Bottle sizes'
Instituto dos Vinhos do Douro e Porto
Originally known as the Instituto do Vinho do Porto (Port Wine Institute), the IVDP was created in 1933 to control the quality and volume of Port production. It is Port's certifying body and is responsible for upholding its reputation and good name. In 2007 its responsibilities extended to the supervision of all wines produced in the Douro Demarcated Region, including table wines, at it was renamed the Instituto dos Vinhos do Douro e Porto (Douro and Port Wine Institute). Although part of the Ministry of Agriculture, the Institute is funded by a levy paid by the Port companies and calculated on the volume of wine sold. The IVDP issues the numbered garantee seals which are placed over the necks of Port bottles to certify their authenticity.