The Maillard Reaction: A Practical Guide

The Maillard reaction is responsible for creating hundreds of aroma and flavor compounds in roasted coffee and by manipulating the roast profile we can exert some control over the flavor of the coffee we roast. What I hope to achieve here is to provide enough practical information to 1) help you immediately improve your roasts and 2) generate interest in the Maillard reaction so that you can dig deeper into its underpinnings.

Phases of the roast profile

Let's start by talking about roast phases. We break concepts down in order to better understand complex ideas and a roast profile is definitely a complex idea. There are no hard-and-fast rules as to how to segment a roast profile when analyzing it but there is general consensus that the three phases are the drying phase, the Maillard phase, and finally the roast development phase. Are the beans only drying in the first phase? No. Is the Maillard reaction only active during the second phase? No. Is the roast only developed in the final phase? No. The names of the phases follow the dominant aspect of that phase and until we get a new consensus on the terminology, we'll have to accept what we have so that at a minimum, we can effectively communicate with each other about our roasts.

For the purpose of this discussion, I call the drying phase as everything before 300°F measured at the bean temp (BT) probe. The Maillard phase happens after 300° and until first crack, which is the beginning of the roast development phase.

Maillard reaction defined

Whether you prefer to produce dark or light roasts, you are leveraging the Maillard reaction. What is the Maillard reaction? In a nutshell, it's the process of combining of sugars with amino acids (protein components) to form melanoidins. What are melanoidins? They're what give roasted coffee it's brown color; they're brown polymers that have a high molecular weight, which for coffee means "body."

So far, this is what our "Maillard phase cheatsheet" reads:

  1. The Maillard phase consumes sugars and amino acids
  2. to produce melanoidins, which contribute to brownness of the roasted beans as well as the body of brewed coff

Feeling the heat

Now let's talk about heat. The rate of heat application is a primary method of affecting the reaction rate; the more aggressive our heat application, the faster the reaction and the more byproducts created in a shorter amount of time. Leveraging this, we can experiment with a faster, but shorter Maillard phase or a slower and shorter Maillard phase to see what these changes do to a target coffee. Which is better? Only experimentation can tell you. This is one of the things about roasting that frustrates newcomers (it certainly frustrated me); no one can honestly tell you that your roast profile should have a 3.5 min drying phase, a 5-minute Maillard phase, and a 5-minute roast development time. The state of the art isn't there yet and frankly, if it were, it would likely be a lot less interesting to a lot of craft roasters.

Okay, let's update our cheatsheet:

  1. The Maillard phase consumes sugars and amino acids
  2. to produce melanoidins, which contribute to brownness of the roasted beans as well as the body of brewed coffee
  3. A higher rate of heat application increases the reaction rate.

What does it taste like?

Now that we've talked about the nuts and bolts of the reaction, let's talk a bit about the dominant flavors it produces. The Maillard reaction produces a lot of nutty, caramelly, chocolatey, malty flavors; flavors that I always interpret as heavy or dark as opposed to floral or fruity flavors, which I perceive as light in weight and light in color (yes, I often visualize or conceptualize tastes as colors).

Our cheat sheet now looks like this:

  1. The Maillard phase consumes sugars and amino acids
  2. to produce melanoidins, which contribute to brownness of the roasted beans as well as the body of brewed coffee
  3. A higher rate of heat application increases the reaction rate
  4. The dominate flavors produced by the reaction are nutty, caramelly, chocolatey, malty flavors

Complexity or clarity?

The Maillard reaction is responsible for creating hundreds of flavor and aroma compounds. Therefore, it may be the single most consequential event in determining the sensorial aspects of the final product, be it a brewed coffee, an espresso, etc.

Because the reaction creates so many different aroma and flavor components, it is also useful in manipulating a coffee's complexity. When looking at two roasts with the same rate of heat application; the longer the reaction proceeds, the more byproducts it creates and the more complex the coffee. Conversely; a shorter reaction time produces a coffee with more clarity. If you have a coffee that has a very dominant floral or fruity character that you would like to showcase, then you want to experiment with shortening or slowing your Maillard phase.

Maillard Reaction Cheat-sheet

So our final cheat sheet for the practical application of the Maillard reaction is this:

  1. The Maillard phase consumes sugars and amino acids
  2. to produce melanoidins, which contribute to brownness of the roasted beans as well as the body of brewed or extracted coffee
  3. A higher rate of heat application increases the reaction rate.
  4. The dominate flavors produced by the reaction are nutty, caramelly, chocolatey, malty flavors
  5. If temps are equal, a longer reaction time = greater number of byproducts = higher complexity + higher body

Exploring the Maillard reaction

While maintaining the same or very similar drying and roast development phases, change the Maillard phase, first by stretching it out by about 30 seconds in time. Do several roasts in the one experiment, and with each roast, make another 30-second change. The next day, cup all of your coffees blindly and compare the results to see not only what the effects are of extending the time of the Maillard phase, but also to see which coffee you like the best.

Repeat the experiment by changing the rate of heat application while keeping the same time in each of the roasts. For example, in roast #1, if the length of the Maillard phase is 4:30, each experimental roast should be the same 4:30 length, but with different rates of heat application, changing each one by 2 - 5°F (hat tip to Rob Hoos).

The key is in exploring by changing only one aspect of the roast at a time and cupping the results.
Hopefully I have given you enough information to first-and-foremost get you roasting a little bit better, regardless of your preferred roast, and hopefully, you are more curious about the Maillard reaction to take a deeper look into its complexities.

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Michael C. Wright

Michael is an American expat living in Singapore where he writes about many things coffee-related. A roaster by trade, Michael is also a licensed Q Grader and an Authorized SCA Trainer (AST).

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