Ernest Cockburn remarked in the early 20th century that ‘the first duty of port is to be red’. Nevertheless a significant proportion of white grapes grow in vineyards in the Douro and all shippers produce a small amount of white port, even if very few give it serious attention. White port is made in much the same way as red except that maceration during fermentation is much shorter, or non-existent. Most white ports have a certain amount of residual sugar, even those labelled ‘dry’ or ‘extra dry’. Intensely sweet wines, made mainly for the domestic market, are labelled lagrima (tears) because of their viscosity (see also málaga). Another, drier style of white port, described as leve seco (light dry) is made by some shippers. These are wines with an alcoholic strength of around 16.5 or 17%, rather than the usual 19 to 20%. Most commercial white ports are aged for no more than 18 months, generally in tanks made of cement or stainless steel. Wood ageing lends character to white port, turning it gold in colour and giving the wine an incisive, dry, nutty tang. Superior white ports may also be bottled with a designation of age: 10, 20, 30, 40 Years Old. White port is sometimes used by shippers for blending cheaper tawnies.