The Maillard reaction: the science behind flavour and colour in foods and beverages 

Sugar is primarily used as a sweetener, but its role extends far beyond that. It is a functional ingredient that plays a critical part in the Maillard reaction, a complex chemical process that occurs when reducing sugars and amino acids interact under heat. This reaction creates the distinctive flavours and appealing colours that we associate with a wide variety of foods, from cookies and cakes to barbecue sauces.  

In this article, we explore the science behind the Maillard reaction, its significance for food and beverage producers, and its applications in everyday industrial products that use sugar.

The Maillard reaction is a chemical process that occurs when reducing sugars and amino acids react under heat. Reducing sugars, such as glucose and fructose, are simple carbohydrates with a free carbonyl group (C=O), which allows them to interact easily with other molecules. Amino acids, the building blocks of proteins, contain both an amino group (NH₂) and a carboxyl group (COOH), enabling them to form bonds with sugars during cooking. This reaction, named after the French chemist Louis Camille Maillard, is responsible for the browning of food and the development of distinct flavours. 

Typically occurring at temperatures above 140°C (284°F), the Maillard reaction plays a key role in cooking methods like roasting, baking and grilling. When heated, sugars such as those in black treacle on glazed gammon or demerara sugar on carrots, interact with amino acids to produce a variety of rich flavours and brown pigments known as melanoidins. These reactions intensify the aroma, colour and taste, enhancing everything from the glossy crust on meats to the toasty-sweet notes in roasted vegetables. 

In baking, the Maillard reaction develops the flavours and enticing aromas of cookies, cakes, and pastries. When crystalline sugars or a sugar syrup like black treacle interact with amino acids in the batter, they create golden surfaces and complex flavour profiles. In cakes, the reaction helps achieve a moist, tender crumb and golden-brown colour. The resulting melanoidins deepen the flavour and colour of these baked goods, making them irresistible to consumers. 

The Maillard reaction enhances flavour, colour, aroma, texture, appearance and stability in some foods and beverage – attributes that underpin consumer acceptance and product shelf life. Below, we explore these attributes in more detail.  

Flavour enhancement: The Maillard reaction creates a variety of flavour compounds that contribute to the savoury, nutty and caramel notes found in various foods, including roasted meats, baked goods and even coffee. For example, the distinctive flavour profile of a black treacle coated gammon is a direct result of the Maillard reaction occurring at high temperatures, where amino acids and reducing sugars react to form hundreds of different compounds, or in products like barbecue sauces, where sugars such as those found in molasses interact with amino acids to develop deep, savoury flavours that consumers crave. This reaction not only enhances taste but also makes food more appealing to consumers, as they often associate rich, complex flavours with quality. 

Colour and appearance: Colour intensity in baked goods and roasted foods is primarily due to the Maillard reaction. This browning effect is a result of the formation of melanoidins, which are responsible for the colour and certain flavour properties of the food. The presence of a rich, brown crust signals to consumers that the food is flavourful and well-prepared. 

Texture and aroma: The Maillard reaction creates attractive textures in various foods. For example, it contributes to the crispy crust of a baguette and the chewiness of a chocolate chip cookie. The complex aromas generated during the reaction are not only inviting but also stimulate appetite, enhancing the appeal of baked goods, drawing consumers in and encouraging them to indulge. 

Food quality and safety: The Maillard reaction enhances the stability and shelf life of food products, which is important for consumer safety and confidence. The browning that occurs in processed meats inhibits microbial growth and extends shelf life. The compounds generated through the Maillard reaction can also possess antioxidant properties, enhancing nutritional value.  

The Maillard reaction is not just a chemical process; it is a fundamental element of food science. By understanding how it impacts food, manufacturers can develop products that meet consumer expectations for flavour, appearance and quality. 

The Maillard reaction is not a single reaction but rather a series of intricate chemical transformations between amino acids and reducing sugars, which mainly occur during the heating of food. By understanding the stages of the Maillard reaction, we can gain insights into how these changes enhance the sensory attributes of food, and how we can use sugar to influence flavour, colour, texture and mouthfeel.  

The Maillard reaction begins with a condensation reaction between a reducing sugar, such as glucose (C₆H₁₂O₆) or fructose (C₆H₁₂O₆), and an amino group (-NH₂) from an amino acid or protein. A condensation reaction is a chemical process in which two molecules combine to form a larger molecule while releasing a small molecule, usually water (H₂O). In this context, the reaction occurs when the carbonyl group of the sugar reacts with the amino group of the amino acid, resulting in the formation of a Schiff’s base (an imine, R₂C=NR’, where R and R’ represent organic groups). 

The Schiff base is an unstable intermediate that quickly rearranges to create a glycosylamine (R₁C(=O)NR₂, where R₁ is derived from the sugar and R₂ is the amino group). The process is facilitated by heat, often starting at temperatures above 140°C (284°F). The glycosylamine is also unstable and quickly rearranges to form an Amadori compound, which is a more stable intermediate denoted by the general structure of R₁C(=O)NR₂R₃, where R₁ is derived from the sugar and R₂ and R₃ represent the amino acid side chains. The Amadori compound serves as a precursor for subsequent reactions in the Maillard reaction, leading to the development of complex flavours and brown pigments in cooked foods. 

As the reaction progresses, the Amadori compound undergoes further transformations, including dehydration and fragmentation. This process generates a variety of reactive carbonyl compounds, such as hydroxymethylfurfural (HMF), pyruvaldehyde and diacetyl. As the sugars and amino acids degrade, this leaves a slightly yellow colour and a rich, complex flavour and aroma. 

In the final stages of the Maillard reaction, intermediate compounds continue to react and undergo a process called aldol condensation. This reaction occurs when aldehydes or ketones – types of organic compounds containing carbonyl groups, formed during earlier stages of the Maillard reaction – react with each other. 

In an aldol reaction, a carbonyl compound (represented as RCHO for aldehydes or R₂C=O for ketones) that has at least one alpha-hydrogen (–CH₂–) acts as a nucleophile—this means it can donate a pair of electrons to form a chemical bond. This nucleophile attacks the carbonyl carbon of another aldehyde or ketone, resulting in the formation of a β-hydroxy aldehyde (R₁R₂C(OH)CHO) or ketone (R₁R₂C(OH)R₃C=O) as an intermediate compound. 

As the reaction proceeds, the β-hydroxy compound can undergo dehydration, which means it loses a molecule of water (H₂O). This step leads to the formation of a conjugated enone (a compound with alternating double bonds, R₁R₂C=CHR₃) or enal (a compound with an aldehyde and a double bond, R₁R₂C=CHCHO). This step is significant in the Maillard reaction because it leads to the formation of larger, more complex compounds that contribute to the development of flavour and colour in cooked foods. 

These reactions result in the formation of melanoidins, which are large, brown compounds responsible for the characteristic colour of cooked foods. Melanoidins also have antioxidant properties, which help improve the shelf life of the final product. 

The efficiency and outcomes of the Maillard reaction are influenced by several key factors:

Temperature: Higher temperatures accelerate the reaction rate, resulting in more pronounced browning and flavour development. For example, in baking, the Maillard reaction is essential for achieving the rich flavours and golden crust of chocolate chip cookies, where sugars and proteins interact during the baking process. 

pH Level:  The reaction thrives in slightly alkaline conditions, enhancing the formation of reactive species. This is why bakers often add bicarbonate of soda (baking soda) to recipes, as the elevated pH promotes browning and flavour development, particularly in cookies and cakes. 

Water activity:  Controlling moisture levels is an important factor, as excess water can hinder the interaction between amino acids and sugars. For example, in meringues, bakers aim for low moisture to ensure crispness and maximise the Maillard reaction, resulting in a delicate texture. 

Type of sugar and amino acid: Different sugars and amino acids can yield distinct flavour profiles and browning characteristics. For example, soft brown light sugar, which contains molasses, adds moisture and enhances the flavour of treats like gingerbread. The additional compounds in molasses contribute to a deeper colour and richer taste, demonstrating how ingredient selection influences the final product. 

Reaction time: Longer cooking times can lead to more pronounced flavours but may also result in bitterness if overcooked. This is especially important in slow-roasting meats, where the Maillard reaction develops complex flavours, requiring careful monitoring to avoid charring. 

Understanding these factors enables food scientists and manufacturers to manipulate cooking conditions and ingredient choices to optimise the sensory attributes of their products, creating a more appealing culinary experience for consumers. 

As we know, the Maillard reaction develops rich, complex flavours in brownies, creating a fudgy texture and glossy finish. Caramelisation and dextrinisation are also distinct browning processes. Each contributes unique flavours, colours and textures to various foods. In industrial baking, these reactions enhance any sugar-rich product. 

Caramelisation enriches the sweetness and colour of pastries, providing that irresistible golden crust. Dextrinisation enhances the crispness and browning in products like crackers and biscuits, contributing to their satisfying crunch. Although different, these reactions often overlap to create delicious treats that elevate the sensory appeal of baked goods for consumers. 

Dextrinisation occurs at lower temperatures of around 120°C (248°F). During this reaction, starches begin to break down into shorter dextrins, which are carbohydrates produced by the hydrolysis of starch. This process imparts a mildly sweet, toasty flavour and adds additional browning, especially in starchy foods like bread and crackers.  

Caramelisation takes place at higher temperatures, generally starting at 160°C (320°F), and only involves sugars. This reaction produces caramel-coloured compounds such as caramelans (C₂₄H₃₆O₁₈), caramelens (C₃₆H₅₀O₂₅), and caramelins (C₁₂₅H₁₈₈O₈₀) which add sweet, nutty, and slightly bitter notes to foods. 

All three reactions can occur simultaneously in foods that contain both proteins and starches, such as bread, pastries, biscuits, cakes, and some sauces and marinades. Together, these processes create a layered sensory profile, enabling food scientists and manufacturers to optimise flavour, colour and texture in their products.

The Maillard reaction has many applications. Some of these we outline below.  

The Maillard reaction is essential for developing the colour and flavour of baked goods, enhancing both texture and aroma. By manipulating sugar content and baking conditions, manufacturers can achieve a diverse range of flavour profiles and textures in products like cookies, biscuits, and crackers, highlighting the significance of Maillard chemistry in their production. 

Sucrose is commonly used in industrial baking due to its stability, which prevents it from readily participating in the Maillard reaction at lower temperatures or in the presence of moisture. This characteristic helps avoid unwanted browning or flavour development during the early stages of food preparation. Since the Maillard reaction occurs at higher temperatures, bakers and chefs can control its timing, allowing them to intentionally initiate browning when desired, such as during the baking of cookies to achieve that perfect golden finish. 

The Maillard reaction underpins crust formation and flavour development. When bread dough is baked, the high temperatures facilitate the Maillard reaction, resulting in a golden-brown crust that contrasts with the soft, tender crumb inside. 

As the sugars and proteins interact, they create complex flavours often described as nutty or caramel-like. This interaction also generates a range of volatile organic compounds (VOCs), such as furans, pyrazines and aldehydes, which contribute to the desirable aromas that attract consumers.  Additionally, the reaction can influence the nutritional profile of the bread by producing antioxidants, providing additional health benefits. 

Different types of bread, such as sourdough and wholegrains, may exhibit varying Maillard reaction characteristics based on their ingredient composition and baking conditions. For instance, the higher acidity in sourdough can impact the reaction’s efficiency, leading to unique flavours and crust colours. 

In confectionery, sugar serves as the primary ingredient, providing structure and bulk and acting as a preservative. In chocolate production, the Maillard reaction generates the rich, complex flavours characteristic of high-quality chocolates. As cocoa beans are roasted, the reaction produces aromatic compounds that deepen the overall taste profile, creating the nuanced flavours that chocolate lovers seek, including fruity, nutty and floral notes. 

The Maillard reaction occurs in the brewing process, particularly during malting and kilning, where sugars and amino acids combine to form melanoidins. These compounds contribute to the rich amber and dark hues of various beer styles, especially stouts and porters, while adding a roasted, caramel flavour. 

In the malting process, grains are soaked and germinated, activating enzymes that convert starches to sugars. Kilning initiates the Maillard reaction, producing melanoidins and other flavour compounds. By adjusting malting temperatures and times, brewers can control these flavours and aromas, crafting complex beer profiles. 

The Maillard reaction also produces pyrazines, furans, and thiazoles, which enhance toasty, malt-forward aromas. By mastering this reaction and adjusting malting temperatures and times, brewers can craft a diverse range of beer styles, from light lagers to robust ales. 

In coffee production, roasting coffee beans initiates the Maillard reaction, forming the melanoidins and complex compounds that give roasted coffee its rich colour and distinctive flavour. The roasting temperature and duration are critical, influencing flavour development, light roasts retain the bean’s natural acidity and fruity notes, while darker roasts yield deeper flavours with chocolatey or smoky undertones. Additionally, the Maillard reaction contributes to the volatile, aromatic compounds that create the inviting smell of freshly brewed coffee. By understanding these nuances, roasters can tailor their processes to create unique flavour profiles that appeal to consumers. 

The Maillard reaction shapes the rich flavours, colours and enticing aromas that characterise some of our favourite sugar-rich foods and drinks, transforming simple ingredients into complex taste experiences. For food and beverage manufacturers, understanding the nuances of the Maillard reaction is essential for developing products that satisfy consumer cravings and elevate quality.  

Ragus manufactures pure sugar syrup and crystalline sugar functional ingredients that enable industrial food and beverage brands to create target flavours, colours and textures. Contact our Customer Services Team to learn more, continue browsing SUGARTALK and follow Ragus on LinkedIn.