As twilight descends on the wide Douro river, the roof mounted lettering on the tops of buildings on the opposite bank light up to reveal Company names advertising their famous wares. Some of them are familiar – Sandemans, Cockburn’s, Taylor’s, Dow’s – others less so, but regardless of whether we know them or not, they are all big names in the business which is literally synonymous with this city. Porto isn’t just cheerful, it’s also full of cheer, contributing significantly to our and every other visitor’s alcoholic intake with its proud history of wine production relentlessly pushed at every corner. Reds, whites and vinho verde from the Douro Valley, port…