Mini Object Lesson: When Does Bread Become Toast?

Editor’s Note: This article previously appeared in a different format as part of The Atlantic’s Notes section, retired in 2021.

Everyone knows what bread is, and everyone knows what toast is. And everyone knows that the first can be transformed into the second. Less clear: when, exactly, does the transformation take place? When does bread become toast?

The browning process we call toasting is an example of the Maillard reaction, in which amino acids and sugars interact to produce the characteristic brown color, texture, and flavor we know as toast. When heat encounters amino acids (many are present in wheat and flour) and sugars, the two rearrange and produce brown polymers (called melanoidins). The Maillard reaction is also responsible for the deep flavors of browned barley in beer, roasted coffee, seared meats, and French fries.

Toast pedants will stress that the Maillard reaction is not the same as caramelization, which is a type of thermal decomposition that chars—that’s what can happens when you toast your toast too long. Too much charring and you’re carbonizing bread, not toasting it.

That’s all well and good, but when, precisely, does bread become toast?

If you search the web, you’ll find endless threads from the tongue-in-cheek clown to the overzealous armchair chemist, all attempting to answer (or to mock) this metaphysical question. Sites leaning more toward geekery embrace scientific answers, while others use toast as an object lesson in the universe’s ultimate mystery.

Is bread toast only insofar as a human toaster perceives it to be “done?” Is bread toast when it reaches some specific level of nonenzymatic browning?

If the former, toast seems more like a performative speech act—“I dub thee toast!” than it is a physical configuration of bread and heat. Toast was first produced with a hand-iron over an open flame, after all, rather than an enclosure called a toaster that enshrouds the process in unnecessary and pregnant secrecy.

If the latter, the epistemological question doesn’t go away, as no toaster I know of can measure and evaluate all the varied configurations of amino acids, sugars, water, and heat. (Please, do not attempt a Kickstarter for such a device.) There are even some who might prefer their toast more on the caramelized or even charred side. Who’s to say that those rare (if not rarified) tastes should preclude the label “toast?”

Perhaps it’s such a welcome and common question because “when does bread become toast” demands that you engage in a fairly complex metaphysical debate on relatively ordinary terms. This isn’t God or nature we’re talking about, but browned bread. And yet, all the frothy urgency and spectacle of more serious matters still pervades such an ordinary substance. This is the ultimate payload of the puzzle: not to find an answer, but to admire that the question can spread so much complexity on to such a modest surface.