The science behind golden brown bread and extra-crispy croissants

You may have caught a recent Facebook post of ours that featured an article by Andrew Janjigian on how to turn any home oven into a pizza oven. While the article itself was praised by many as helpful (thanks, Andrew!), the image we used roused some rather — how can we put this lightly? — passionate responses.  

Our comments section rang out with critical declarations of “That's burnt!” and “I’d send it back!” as well as supportive retorts like “That's how it should look!”    

At the risk — or benefit — of continuing that discussion, here is the “offending” image:  

Rick Holbrook

While we pause to consider which side of the great “King Arthur Facebook Pizza” debate we fall on, let’s also take this opportunity to chat about what’s going on in this photo. Rather than argue whether this pizza is burnt or not (don’t ask us, we’re Switzerland), what we can — and should — discuss is how what’s happening here, on a chemical level at least, plays an essential part in baking success. 

What’s happening here is called the Maillard reaction.  

From fried eggs and marshmallows to meat, vegetables, and yes, pizza, the Maillard reaction is, in essence, why foods brown when heat is applied. But more than that, the Maillard reaction gives our food flavor. Ever wonder why we’re so drawn to the “toasted popcorn” taste of a freshly baked baguette or, well, toasted popcorn? That’s the Maillard reaction: A curious outcome of what happens when proteins and sugars get all hot and bothered, and why, oftentimes, “browned” foods just taste better.  

From a baking perspective, understanding the various ways the Maillard reaction affects our bakes can elevate them from “pretty good” to “exceptional.” Because it’s one thing to know why our crust crackles and tastes good, and a totally different thing to know how to manipulate the science to make it happen.  

With that in mind, let’s begin this (very) short introduction at the beginning, with Maillard himself. 

That’s pronounced “my-ard” not “mallard”  

The Maillard reaction is named for Louis Camille Maillard, a French chemist who first published his discovery in 1912. While conducting research on protein synthesis, Maillard found that when combining amino acids (organic molecules that combine to make proteins) with sugar alcohol in a tube filled with water, and then heating it, the liquid took on a yellow hue. The longer and higher he heated it, the darker the color until it finally turned dark brown.

At its most basic level, the Maillard reaction is quite simple. When our food is heated to a temperature of at least 280°F, a chemical reaction occurs between amino acids (proteins) and carbohydrates (sugars) that causes it to brown. So essentially: protein + sugar + heat = browning.

What this also does is add unique flavors. As they begin to interact with heat, the amino acid proteins produce nitrogen and sulfur atoms that then bond to the existent carbon, hydrogen, and oxygen in the chemical makeup of what we’re heating. The result is a far more complex flavor profile than with other types of browning, like caramelization, which merely involves the chemical breakdown of sugar until it liquifies and turns yellow and then brown. The result: the Maillard reaction produces more attractive and flavorful food.

Raymond Prado

When we want Maillard in baking … and when we don’t 

Making sense of Maillard reactions — and how to manipulate them — can be essential to baking success. Especially when it comes to unwanted flavors. When taken too far, the bitter taste of burnt food can be unpleasant; on the other end of the spectrum, a weak Maillard reaction can lead to an equally disappointing blandness.    

Think of it this way: Who here has baked a loaf of bread that turned out bland and pale? Us too. Among other things, one common culprit is overproofing. During the proofing stage, yeast eats the carbohydrates (sugar) in the dough, which in turn creates carbon dioxide gas. In overproofed dough, the yeast eats up too much of those carbohydrates, so when we bake our overproofed dough, the amino acid proteins in there don’t have as much sugar to interact with. And since sugar + protein + heat = browning, we get a lackluster Maillard reaction and a sad crust.  

Baker's tip: The same acidity that gives sourdough bread its distinct flavor will also hinder Maillard reactions, since acidic conditions will slow the browning process. The next time you find yourself disappointed by the pallid color of your sourdough, keep in mind that it’s sometimes supposed to look like that.  

Frankie Gaw

But this isn’t always a bad thing. Sometimes, we want to prevent Maillard in our bakes. Like when making steamed buns. Cooking dough with steam keeps the temperature lower than the 280°F at which Maillard reactions occur (steam is produced at around 212°F), and what's more, the Maillard reaction can’t occur in the presence of water. This means that rather than developing a deep golden and crackling crust (like a loaf of sourdough), our buns remain soft, fluffy, and perfectly pale — the preferred outcome when we want our fillings to take center stage.  

And this Maillard manipulation can be applied in other ways. Have you ever wondered why we put baking soda or lye in the water bath for pretzels? They're alkaline substances, which means they alter pH levels (how acidic something is). When we quickly boil our pretzel dough in an alkaline bath, the alkali in the water modifies the proteins on the surface of the dough. Or, as one of our Baking School experts, Jess Meyers, tells her pretzel class: “In essence, that simple water bath alters the pH level in the dough, giving the Maillard reaction an accelerated boost, resulting in deep brown, glossy pretzels with classic surface cracks.”

Kristin Teig

You’ve seen this science elsewhere. You know that flaky, crispy, irresistible exterior of a croissant? Same principle, different application. Just before we bake our croissants, we give the dough a quick egg wash (like we do with our new Recipe of the Year Ultimate Sandwich Bagels). The additional proteins in both the yolk and egg white give the Maillard reaction the same boost the alkaline bath gave our pretzels, helping those laminated layers brown up. (What’s more, while the yolk adds additional fat and pigment, the white gives them a glossy shine — yet another way manipulating the science of baking can work in our favor!) Bake them without the egg wash, and the lesser Maillard reaction will leave croissants and other bakes wan.  

That’s where the flavor comes from

So, there we have it. A (very) short introduction to the Maillard reaction, and how manipulating it can elevate our baking from pale to perfection — as long as that’s what we’re going for. Which brings us back to our original pizza image and the inciting question: Is it burnt?  

Rick Holbrook

Certainly, there’s some heavy browning going on, plus something darker: those famous “leopard spots” pizza aficionados rave about. But would we say it’s beyond repair? Inedible? Worth sending back? Or is this the way it should be?  

Maybe now that we know a bit more, perhaps the better question would be: Is it a good example of the Maillard reaction? After all, dark hues like this are evidence of a healthy thermal interaction between amino acids and carbohydrates. Which also means the baker has done a good job manipulating Maillard in their favor. So, if we were truly dead set on determining if this pizza was a success, by looks alone, the answer would be “yes.” And let’s not also forget, when it comes to Maillard reactions and baking, that is where the flavor comes from. 

The Maillard reaction helps your breads get dark, but you may be wondering how dark, exactly, they should be. For baking advice, see our previous post, Ask the Bread Coach: Just how dark should I be baking my bread?.

Cover photo of Honey-Beer Miche by Rick Holbrook.