If you are going to ground your pork, remove the skin and leave the fatty layer. Grind the pork finely using a meat grinder or food processor. To make the achuete oil, soak 2 Tbsp. achuete seeds in 2 Tbsp. cooking oil for an hour. Remove the seeds and set aside the achuete oil.
In a mixing bowl combine pork, vinegar, garlic, sugar, pepper, salt and achuete oil. Mix all the ingredients until well combined. Chill the mixture for at least 5 hours or overnight.
Form the meat mixture into logs about and inch in diameter and 3 to 4 inches long. You can use wax paper to make the logs and cut it about 6 inches by 4 inches. Form the mixture into logs and roll in wax paper.
Put longganisa in a baking sheet and put in a freezer until frozen. Transfer to plastic bags or plastic containers and put back in the freezer for storing.
To cook the longganisa, you can fry it directly in cooking oil in low heat until brown to prevent burning the longganisa and still raw inside. You can also put some water in the pan and boil the longganisa until the liquid evaporates. Then put some cooking oil and fry it until cooked.