Kashrut
Among the numerous laws that form "kashrut" are prohibitions on the consumption of certain animals (such as pork and shellfish), mixtures of meat and milk, and the commandment to slaughter mammals and birds according to a process known as "shechita". There are also laws regarding agricultural produce that might impact the suitability of food for consumption.
Portuguese cuisine
Alentejo is a vast agricultural province with only one sizeable fishing port, Sines; and in the past, shellfish would not have been available in the inland areas. On the other hand, all points in the Algarve are relatively close to the coast and pigs used to be fed with fish, so clams were added to the fried pork to disguise the fishy taste of the meat. Nowadays, however, nobody would dream of calling it "carne de porco à Algarvia". Legend also says that the dish was developed to test Jewish converts' new Christian faith; consisting of pork and shellfish (two non-kosher items), "Marranos" were expected to eat the dish in public in order to prove their complete detachment from the Jewish faith.