To stuff sausage meat into casings, you will need either the sausage horn attachment for a meat grinder or a pastry bag fitted with a plain tip. You will need about 8 feet of medium hog casings, available from specialty butchers or by mail-order (see note). Soak the casings, which come packed in salts, in warm water in a large bowl for 30 minutes to 1 hour. Then put one end of a casing over the end of a faucet and wash the inside with warm water. Change the water in the bowl and soak the casing again.
If you're using a grinder,
remove the plate and knife and fit it with the sausage horn. Pull the entire length of soaked casing over the tip of the horn, gathering it up and leaving a little bit dangling. Tie a knot in the dangling end. Fill the bowl of the grinder with chilled sausage meat and crank the meat through the grinder to fill the casing. Continue to feed the meat through the grinder into the casing until all the meat is used up. Use a skewer, pin, or needle to prick any air bubbles that form as the casing fills. The casing should be full, but not too tightly packed, or it will burst when you form the links. Remove the casing from the horn.
If you're using a pastry bag,
pull the entire length of casing over the end of the tip, gathering it up and leaving a little bit dangling. Tie a knot in the dangling end of the casing and fill the pastry bag with chilled sausage meat. Squeeze the bag with one hand to push the meat into the casing while you use your other hand to hold the casing on the metal tip. Fill the casing with all the meat, as described above. When it is filled, remove it from the pastry bag.
To form the links,
begin at the knotted end and pinch the casing between your fingers about 5 inches from the end; you may vary the length if you wish. Move down the casing another 5 inches and pinch again, about 10 inches from the knot. Twist the second 5-inch section with your fingers to make the first two links (twisting the link will twist both ends and seal both links). Proceed down the casing, twisting every other pinch to make links. When you reach the end, tie another knot.
To separate the chain into links,
use a sharp knife to cut through the twisted casing to make individual sausages. Refrigerate them right away and use within 2 to 3 days. Or wrap them in plastic wrap or foil and freeze for up to 3 months.