From an Atlantic piece by Wayne Curtis about flaming cocktails:
At Booker and Dax, part of the Momofuku empire in Manhattan, “red-hot poker” drinks are made with electrically charged rods modeled after the colonial-era loggerhead, a tool used to keep tar pliable. The modern version heats up to 1,500 degrees, and when it’s plunged into a drink, it caramelizes the sugars, giving the beverage a slightly butterscotchy flavor and a toasted top note.I’ve known the word loggerhead only as part of the idiom at loggerheads, which describes two parties or sides stubbornly disagreeing. The idiom makes me think of two logs butting heads, so to speak, and of a logjam, an impasse.
The Oxford English Dictionary gives the earliest meaning of the word: “A thick-headed or stupid person; a blockhead” (1595). And shortly thereafter: “A head out of proportion to the body; a large or ‘thick’ head” (1598). So my folk etymology seems (to me anyway) plausible. But here is “sense 3”: “An iron instrument with a long handle and a ball or bulb at the end used, when heated in the fire, for melting pitch and for heating liquids” (1687).
The OED ’s speculation about the idiom has nothing to do with blockheads: “The use is of obscure origin; perhaps the instrument described in sense 3, or something similar, may have been used as a weapon.” And now I’m confused, as the idiom (dated to 1671) predates “sense 3” (1687). But I’m not at loggerheads with the OED. Perhaps the tool was known as a loggerhead for some time before the word entered the written record.
Check Wikipedia for loggerhead and you’ll find a photograph of Wayne Curtis himself, in colonial regalia, standing before a table that holds a pineapple, a pitcher, a propane torch, several bottles, and a loggerhead. Try a Google Image search for a loggerhead though, and it's turtles all the way down, at least since 1657.
A tenuously related post
Little Baby Turtle (pehaps a loggerhead)