Coffee Roasting Basics: What Is The Maillard Reaction?

Matteo Pavoni
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April 29, 2021
maillard reaction coffee roasting

Roasting is a fundamental stage in a coffee’s journey from seed to cup. Not only does it unlock the potential of green beans by releasing thousands of aromatic compounds, it also makes them brittle and porous enough to effectively grind and brew.

During roasting, several complex chemical reactions occur that have a significant impact on a coffee’s final flavour. One of the important is the Maillard reaction, also known as the “browning phase”, which occurs when sugars and proteins are subjected to heat.

For specialty roasters, understanding the Maillard reaction is vital to bringing out the best flavours and achieving the desired roast profile of each coffee.

To find out more about this crucial stage in the development of coffee and how to control it, I spoke with WBC-certified judge and WCE representative, Danilo Lodi.

See also: Coffee Roasting Basics: A Short Guide To Sample Roasts

maillard reaction

What Are The Different Phases Of Coffee Roasting?

The term “coffee roasting” encompasses a number of different phases that occur from the moment green coffee is charged into the drum to the very end of the roast.

During each phase, countless chemical reactions take place that have an impact on the final flavour of the coffee. These reactions help transform dull-tasting green beans into an aromatic and flavourful product that’s ready to grind and brew.

According to most coffee roasting experts, a typical roast can be divided into three key phases. They are as follows:

Drying phase

When green beans are charged into a roaster, a sharp drop in temperature is recorded as the cool beans come into contact with the hot drum. After a short time, the beans and the drum reach a “turning point”, in which the temperatures of both are the same, before they start to rise in parallel.

The main transformational changes that occur in this phase are an increase in bean volume and internal pressure (due to the transformation of water into steam), loss of mass and density, and a colour change from green to yellow.

According to coffee consultant Rob Hoos, the length of time and the temperature of the drum during the drying phase are critical to the overall development of a roast. Generally, it should be around 40% of the entire duration. 

Caramelisation

The caramelisation phase is generally considered to be the time between the beans turning yellow and “first crack” (when pressure inside the beans causes them to burst open). Its name refers to the breakdown, or caramelisation, of many of the sugars inside the coffee beans.

The most important of these caramelisation reactions is known as the Maillard reaction, a non-enzymatic reaction between amino acids and reducing sugars that causes coffee beans to “brown”. The reaction also produces an abundance of flavour and aromatic compounds in the coffee, which contributes to its distinct taste.

Danilo has worked in the coffee industry for more than 17 years and has considerable experience of coffee roasting. He tells me that controlling the length of the Maillard reaction and the rate at which it occurs is crucial to achieving desired flavour and roast profiles.

“It’s important to make a note of precisely when the Maillard reaction starts, how long it took to get it, and how long it lasts,” he says.

Maillard reactions tend to produce savoury, floral, chocolatey, earthy, and roasted aromas, among others.

First crack & development phase

The third phase starts at first crack and finishes at the end of the roast cycle, with the final temperature dependent on the desired roast profile. 

As first crack, numerous chemical reactions occur very quickly, with the rate at which they occur largely defined by the momentum set by decisions made earlier in the roast. 

Along with the coffee’s final temperature, these reactions most clearly modulate a coffee’s sweetness and acidity. Generally, the shorter a coffee spends in development and the lower its final temperature, the more it will express sweetness and acidity. 

On the other hand, the longer it spends in development and the higher its final temperature, the more it will express caramelised or roasted character with lower acidity. This is also the phase of a roast when the darkness of a roast is determined: the longer the development time, the darker the roast.

flavour profiles

How Does The Maillard Reaction Affect The Flavour Of Coffee?

According to coffee roasting expert Rob Hoos, manipulating the Maillard reaction can have a significant impact on a coffee’s characteristics. 

For example, roasters can raise the complexity of the sugar browning, as well as increasing texture and mouthfeel by lengthening the Maillard reaction. Conversely, a shorter reaction tends to soften body and mouthfeel, while reducing complexity in sweetness and flavours.

“Generally speaking, if you reach the Maillard reaction too quickly, you’re going to leave too many organic acids in the cup, which will be unpleasant,” Danilo explains. “But if you take too long in this phase, then you’re going to dissolve too many solubles in the coffee, which could produce more body but with dirty, earthy tones.”

Part of the reason for these differences is down to melanoidins. Melanoidins are brown nitrogen-containing polymers that form in roasted coffee during the Maillard reaction. As well as flavour, they have a considerable impact on the viscosity of coffee when brewed.

The longer the Maillard reaction, the more melanoidins are produced and the higher the molecular weight of the beans. This is why characteristics such as mouthfeel and body differ across different roast profiles from the same batch of coffee.

sustainable coffee packaging

Do Different Roast Profiles Require Different Packaging?

For specialty roasters, it can be difficult to learn how to manipulate the Maillard reaction to bring out specific characteristics of a coffee. However, once they’ve mastered it, they need to make sure customers know what qualities to expect by using packaging.

To highlight qualities such as acidity and sweetness, roasters can leverage colour and shape psychology to influence customer perceptions. For example, research shows that green and angular labels on coffee packaging can be used to denote higher acidity, while pink and round labels suggest sweetness.

However, it’s not just the characteristics produced by the Maillard reaction that might encourage roasters to choose different packaging. According to Danilo, its impact on the level of CO2 inside the coffee beans means that rates of degassing also need to be considered.

“Normally a longer Maillard reaction will lead to a higher weight loss compared to other coffees, creating more gas and therefore more expansion in the closed bag during the first few days after roasting,” he says. “That being said, I don’t think you necessarily need different packaging. Rather, keep in mind how much coffee you put into the bag at once and make sure to leave enough space for proper degassing.”

As an additional measure, roasters should include degassing valves on their packaging, particularly for coffee with darker roast profiles. Degassing valves are one-way vents that allow built-up CO2 to escape without letting oxygen enter.

compostable coffee bags

The Maillard reaction is essential to the development of a coffee’s characteristics, affecting everything from flavour notes and bitterness, to body and mouthfeel. Therefore, it’s vital for specialty roasters to understand how to manipulate the Maillard reaction to unlock the full potential of their coffee and achieve the desired roast profile.

At MTPak Coffee, we offer a range of sustainable packaging options that will protect your coffee and preserve its freshness. Our BPA-free degassing valves are 100% recyclable, while our design services can help you showcase your coffee’s distinct characteristics.

For more information on our sustainable coffee packaging, contact our team here.

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Coffee Roasting Basics: What Is The Maillard Reaction?
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