Q: How did “heat up” replace “heat” in referring to heating food? And why has the equally awful “early on” become so popular?
A: “Heat up” hasn’t replaced “heat” in the kitchen, but the use of the phrasal verb in this sense has apparently increased in popularity in recent years while the use of the simple verb has decreased.
A search with Google’s Ngram Viewer, which compares phrases in digitized books, indicates that “heat the soup” was still more popular than “heat up the soup” as of 2008 (the latest searchable date), though the gap between them narrowed dramatically after the mid-1980s.
However, we haven’t found any standard dictionary or usage guide that considers “heat up” any less standard than “heat” in the cooking sense.
Merriam-Webster online defines the phrasal verb as “to cause (something) to become warm or hot,” and gives this example: “Could you heat up the vegetables, please?”
You seem to think that “heat up” is redundant. We disagree.
As you probably know, “up” is an adverb as well as a preposition. In the phrasal verb “heat up,” it’s an adverb that reinforces the meaning of the verb. (A phrasal verb consists of a verb plus one or more linguistic elements, usually an adverb or a preposition.)
In a 2012 post entitled “Uppity Language,” we quote the Oxford English Dictionary as saying the adverb “up” in a phrasal verb can express “to or towards a state of completion or finality,” a sense that frequently serves “to emphasize the import of the verb.”
The OED, an etymological dictionary based on historical evidence, doesn’t mention “heat up” in that sense, but it cites “eat up,” “swallow up,” “boil up,” “beat up,” “dry up,” “finish up,” “heal up,” and many other phrasal verbs in which “up” is used to express bringing something to fruition, especially for emphasis.
Our impression is that people may also feel that it’s more informal to “heat up” food than simply “heat” it, though dictionaries don’t make that distinction. The phrasal verb “hot up” is used similarly in British English as well as in the American South and South Midland, and dictionaries generally regard that usage as informal, colloquial, or slang.
We also feel that people may tend to use “heat up” for reheating food that’s already cooked, and “heat” by itself for heating food that’s prepared from scratch. An Ngram search got well over a hundred hits for “heat up the leftovers,” but none for “heat the leftovers.” However, we haven’t found any dictionaries that make this distinction either.
In addition to its food sense, “heat up” can also mean “to become more active, intense, or angry,” according to Merriam-Webster online, which cites these examples: “Their conversation started to heat up” …. “Competition between the two companies is heating up.”
And the adverb “up” can have many other meanings in phrasal verbs: from a lower level (“pick up,” “lift up”), out of the ground (“dig up,” “sprout up”), on one’s feet (“get up,” “stand up”), separate or sever (“break up,” “tear up”), and so on.
When the verb “heat” appeared in Old English (spelled hǽtan, haten, hatten, etc.), it was intransitive (without an object) and meant to become hot. The earliest citation in the Oxford English Dictionary is from a Latin-Old English entry in the Epinal Glossary, which the OED dates at sometime before 700: “Calentes, haetendae.”
The first OED citation for the verb used transitively (with an object) to mean make (something) hot is from Old English Leechdoms, a collection of medical remedies dating from around 1000: “hæt scenc fulne wines” (“heat a cup full of wine”).
As far as we can tell, the phrasal verb “heat up” appeared in the second half of the 19th century, though not in its cooking sense. The earliest example we’ve seen is from an April 9, 1878, report by the US Patent Office about an invention in which a system of pipes “is employed to heat up the feedwater of a steam-boiler.”
A lecture in London a few years later touches on cooking: “Now a Bunsen burner will roast meat very well, provided that the products of combustion are not poured straight on to whatever is being cooked; the flame must be used to heat up the walls of the roaster, and the radiant heat from the walls must roast the meat.” (The talk on the use of coal gas was given on Dec. 15, 1884, and published in the Journal of the Society of Arts, Jan. 9, 1885.)
The earliest example we’ve seen for “heat up” used in the precise sense you’re asking about is from a recipe for shrimp puree in Mrs. Roundell’s Practical Cookery Book (1898), by Mrs. Charles Roundell (Julia Anne Elizabeth Roundell):
“bring to the boil, skimming off any scum that may rise, then cool, and pass all through the sieve into another stewpan, stir in the shrimps that were reserved for garnish and heat up.”
As for the adverbial phrase “early on,” it’s been used regularly since the mid-18th century to mean “at an initial or early stage,” according to the OED. The dictionary also cites examples of the variant “earlier on” from the mid-19th century.
Oxford’s earliest example of “early on” is from a 1759 book about tropical diseases by the English physician William Hillary: “When I am called so early on in the Disease … I can strictly pursue it” (from Observations on the Changes of the Air, and the Concomitant Epidemical Diseases in the Island of Barbados).
And the first “earlier on” example is from the Manchester Guardian, April 21, 1841: “It took place earlier on in the year.”
You’re right that “early on” has grown in popularity lately, though “earlier on” has remained relatively stable, according to a comparison of the phrases in the Ngram Viewer.
However, we don’t see why the usage bothers you. The four online standard dictionaries we’ve consulted (Merriam-Webster, American Heritage, Oxford, and Longman), list it without comment—that is, as standard English.