Grana Padano is a Protected Designation Origin cheese since 1996, which means it can be produced only by selected cheese factories only in Po Valley. Grana Padano is characterised by its aging, which can last until 24 months and thickens the crust but leaves the cheese inside crumbly and grainy. Cistercian monks are believed to be the first to produce Grana Padano to stock the overflowed milk into a long-life product.