Red Port is blended together using a number of grape varieties. The precise identity of these, and the proportion each represents in the final blend, may not be known even to the winemaker. For some growers in the 
Douro region of Portugal, the ambiguity over what is in their fortified wines is not an attempt to protect some proprietary secret, but rather a matter of reality: they simply don’t know for sure what they have growing in their vineyards.