The production of Pecorino cheese aged under ash is strictly linked to the method of cheese preservation dating back to the Etrurians. Raw ewe’s milk is filtered and gently heated to 37°C (99°F); this step may take up to 40 minutes. Once heated, liquid calf rennet is added and coagulation takes place in 30 minutes. The curd is cut to walnut-sized grains pieces and, after 5 minutes, placed in moulds. The cheese is left in the mould for minimum 12 hours and turned several times; it is then dry salted. The cheese is aged on wooden boards in a tufa cave, where humidity, temperature and ventilation are practically constant during the whole year. After 10 days, the cheese is placed in terracotta pots and covered with apple and mastic tree.