In a small bowl, stir together sugar, oregano, ginger, pepper, salt, and curing salt until evenly combined; set aside. Mix together garlic, ground pork, and ground pork fat in a large bowl until combined. Sprinkle with spice mixture, pour in white vinegar, and mix thoroughly.
Rinse the sausage casings very well until all of the salt or brine is gone; tie a knot at one end of the casing, then thread the other end onto a sausage stuffing tube. Stuff the casing with the sausage mixture, twisting the filled casing every 2 1/2 to 4 inches to form links. Once all of the sausage mixture has been used, tie the end of the last link.
Using fine cotton kitchen twine, tie the ends of each sausage link tightly, then cut between each link to separate. Place into a glass or plastic container, cover, and allow to mature in the refrigerator for 4 days, after which point they may be frozen.
To cook the longanisa, fill a skillet with 1/2 to 3/4 inches of water and add thawed sausages. Simmer over medium-high heat until the water evaporates, about 20 minutes. Uncover, and allow the sausages to fry in their own oil until golden brown, about 8 minutes more.