The climate is seriously continental, hot and dry in summer, but with very cold, long winters. In the summer and autumn heat, alcohol levels can shoot up before tannins are fully ripened, but with care and skill, good, balanced wines can be made. Ripening is easier in the southern sub-region, Cova da Beira, whose exclusive local white grape, Fonte Cal, can make rich, honeyed wines with steely acidity. Other white varieties include Arinto, Malvasia Fina, Rabo de Ovelha and Síria. The main red varieties are Bastardo, Marufo, Rufete, Tinta Roriz and Touriga Nacional. Many vines are old – a plus for quality, meaning small yields and potentially greater concentration in the grapes.