or side of the machine. Chaff may also be emptied into a bagger, which puts the silage into a large plastic bag that is laid out on the ground. In North America, Australia, northwestern Europe, and New Zealand it is common for silage to be placed in large heaps on the ground, rolled by tractor to push out the air, then covered with plastic sheets that are held down by used tires or tire ring walls. In New Zealand and Northern Europe, 'clamps' made of concrete or old wooden railway ties (sleepers) and built into the side of a bank are sometimes used. The chopped grass can then be dumped in at the top, to be drawn from the bottom in winter. This requires considerable effort to compress the stack in the silo to cure it properly. Again, the pit is covered with plastic sheet and weighed down with tires. In an alternative method, the cut vegetation is formed into bales using a baler, making balage (North America) or silage bales (UK, Australia, New Zealand). The grass or other forage is cut and partly dried until it contains 30–40% moisture (much drier than bulk silage, but too damp to be stored as dry hay). It is then made into large bales which are wrapped tightly in plastic to exclude air. The plastic may wrap the whole of each cylindrical or cuboid bale, or be wrapped around only the curved sides of a cylindrical bale, leaving the ends uncovered. In this case, the bales are placed tightly end to end on the ground, making a long continuous "sausage" of silage, often at the side of a field. The wrapping may be performed by a bale wrapper, while the baled silage is handled using a bale handler or a front-loader, either impaling the bale on a flap, or by using a special grab. The flaps do not hole the bales. In the UK, baled silage is most often made in round bales about , individually wrapped with four to six layers of "bale wrap plastic" (black, white or green 25-micrometre stretch film). The percentage of dry matter can vary from about 20% dry matter upwards. The continuous "sausage" referred to above is made with a special machine which wraps the bales as they are pushed through a rotating hoop which applies the bale wrap to the outside of the bales (round or