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Guimaraens and his family greatly expanded Fonseca's commercial interest in the Port wine industry as well as its vineyard holdings in the Douro. In 1948, the large Port wine corporation of Taylor, Fladgate and Yeatman purchased the house but allowed Fonseca to remain its own separate entity. The Guimaraens family has been intimately involved in the winemaking production with nearly every single vintage label Port from 1896 being made by Frank Guimaraens, his great nephew Bruce Guimaraens and now Bruce's son David Guimaraens. One notable exception is the 1955 vintage which was made by Frank's daughter Dorothy after her father died and before Bruce was ready.