Plain or not? That was the question of people in the Middle Ages. Spices were an important part of the people’s diet. Spices added flavor to the daily meal; the product disguised the taste of bad meat as no refrigeration was available. Traders from the Far East and the Middle East brought a variety of spices to Europe while others were available locally.
The most important additive was salt. During some parts of history, salt or sodium chloride, was worth as much or more than gold. The chemical has been used to preserve meats & fish and enhance recipes since 6000 B.C. Salt was obtained in many of the same methods we use today: mining or evaporating water. It was also used in the dying process and in the making of soap (among others).
Pepper was obtained from India and the Mediterranean. In addition to cooking, pepper was used in medicine. Cinnamon, cloves, ginger, mace, mustard, galanga (a root similar to ginger), cardamom, cumin, coriander, turmeric, anise, caraway, and nutmeg were important parts of cooking. These could be expensive due to the costs of trade expeditions to obtain them. Saffron was used in the dye process.