Sardines are one of the best available sources of vitamin B12, which is important for supporting cardiovascular health. They are also rich in selenium, phosphorus, omega-3 fatty acids, protein, and vitamin D (which facilitates normal immune system function). In addition, they contain significant amounts of calcium, vitamin B3, vitamin B2, copper, and choline.
Ortiz buy their sardines at auction houses (lonjas) on the north coast of Spain. The fish are carefully beheaded and gutted by hand before being washed and prepared for cooking.
They are briefly fried in oil before being tinned in olive oil, "a la antigua" describes this process which leaves the silver skin on the fish.