A melt is converted into pieces by being converted to individual quantities that are dropped onto a cooling surface. Disposed above the cooling surface is a hood having a suction outlet for conducting waste air to a cleaner. Disposed in the hood upstream of the suction outlet is an arrangement of surfaces defining a serpentine flow path for the waste air so that a vaporous component of the waste air crystallizes on the surfaces. The surfaces are formed by plates mounted on a common transport carrier which periodically moves the plates against a scraper for scraping off the crystallized material. Alternately, the surfaces can be defined by endless belts which move against scrapers.