If they are, they must not know the meaning of sumptuous. English-speaking cooks who use unctuous to describe pork roasts are referring to taste, texture, and juiciness. The word sumptuous, although often used to describe a meal, has nothing to do with the taste of food.
The word sumptuous derives from the Latin verb sūmĕre, “to take, consume, spend.” From the verb comes the Latin adjective sumptuosus, “costly, expensive.”
At different periods of history, governments passed what were called “sumptuary laws,” laws that criminalized overspending by certain social classes.
The expression “born to the purple,” meaning, “born into the royal family,” comes from sumptuary laws that restricted the use of an expensive dye called Tyrian purple. In ancient Rome, for example, only the emperor could wear a Tyrian purple cape trimmed in golden thread. Only senators were permitted to decorate their togas with a Tyrian purple stripe.
European sumptuary laws were enacted throughout the Middle Ages and the Renaissance and even found their way to the New World. The Massachusetts Bay Colony passed a sumptuary law to limit the wearing of lace, gold buttons, ruffles, capes, and other expensive items to citizens with a net worth of 200 pounds or more.
A sumptuous meal is an expensive meal. It will have numerous courses made up of a wide variety of dishes and drinks.
Here’s a description of a sumptuous dinner offered at the cost of $99,300 by a caterer to the rich and famous:
The dinner includes ritzy ingredients such as duck eggs and truffles, as well as a dish of Wagyu beef touched with silver leaf that’s served on a bed of dry ice. Each dish in the eight-course meal is combined with a fine wine, such as the $27,680 bottle of La Romanee-Conti, Domaine de la Romanee-Conti, 1990. The price tag also includes a harpist, a poet and doves, as well as chef Adam Simmonds, who earned a Michelin star in 2006.
One can probably assume that such an expensive and lavishly produced meal would include well prepared, tasty food, but not necessarily. It would be possible for a sumptuous meal to be lacking in palate-pleasing food.
Another reader suggests that unctuous may be a mistake for scrumptious; an interesting thought, as scrumptious is a colloquial coinage thought to be an altered form of sumptuous.
Initially, expensive or luxurious things were described as scrumptious, for example, “a scrumptious house.” Then, scrumptious became a general term of enthusiastic praise like wizard or smashing, for example, “That portrait of Thomas More is really scrumptious!” Finally, because it must have often been applied to food, scrumptious came to mean delicious.
Another comment points to a possible explanation for the trending use of unctuous with English-speaking cooks: onctuex (feminine, onctueuse) is used by French cooks to describe food that is creamy. However, I can’t think that a word meaning creamy is exactly the right one to describe a pork roast.
English has enough adjectives to describe things that taste good without resorting to unctuous or scrumptious. Here are a few: