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Store bought casing usually will come packaged in brine or salt. Thoroughly rinse the casing in lukewarm water to remove traces of the salt. If the casing is too long to work with easily, cut off a manageable length. Tie a double knot at this end. When it's filled, remove the funnel and tie a double knot at the end of the rope of sausage. At each interval, twist the rope several times. You can also use cooking twine to tie the ends. This will help prevent the sausages from bursting while cooking later.

Summary:
Prepare the casing. Ease the casing onto the nozzle of a funnel, leaving 2 inches (5.1 cm). Scoop the meat mixture, a small amount at a time, into the funnel and gently pack into the casing. Create small, individual sausages by pinching the rope at even intervals. Using a toothpick or fork, gently prick a few holes into the skin of each sausage. Dry the sausages in the refrigerator before cooking or freezing.