It's packed with so much garlic and vinegar that the acidity itself was traditionally relied on to help preserve the sausage in the days before refrigeration was common.
Coarsely chopped pork is mixed heavy-handed with garlic, vinegar, and salt, stuffed into casings, and left to cure before frying in its own rendered fat. Vigan's market vendors and breakfast stalls sell it grilled or pan-fried alongside garlic rice and a fried egg.