Kulfi Science: How Maillard reaction gives Kulfi its light brown colour?

The reaction that makes Kulfi a unique flavourful feast

Every year during summers, I, like my mother, and her mother before her, used to wait for the Kulfiwala (Kulfi Seller) to arrive in our street in the evening and the moment we heard him shouting his arrival, we would step out of our home to greet him and buy kulfis to treat our sweet tooth. There’s no denying its power to tempt and make people fall in love with it. For those of you who are not familiar with this term, ‘kulfi’ is a popular Indian frozen dessert made from simple ingredients such as milk, table sugar and cardamom seeds (elaichi). You can also add nuts (and other ingredients) to the recipe. 

But have you ever wondered why traditional Kulfi, which is made from milk that is white in colour, is light brown or cream in colour? And why does kulfi tastes so much better than milk?

The most common method to make kulfi is a batch cooking process.  In this process, you heat the milk up to the boiling point (around 100.5°C) and then let it simmer for hours to evaporate the water molecules from the milk and make the milk thicker. The water content in milk can range from 83 to 91 percent (depending upon the animal from which the milk has been sourced). Since water is such a major constituent of milk, this process of heating and evaporating milk can last for hours. You can add table sugar, cardamom seeds and any other ingredients as per the requirements of the recipe. Once the process is complete, this mix is cooled, frozen and ta-dah! you have a bowl of deliciousness ready to be served.

This kulfi making process may seem very simple but it is actually complex on the molecular level. The light brown colour and unique flavour of Kulfi is a result of a series of chemical reactions that begins with the heating of milk. Food scientists call it the Maillard Reaction.

So what is Maillard Reaction?

Maillard Reaction, first reported by Louis-Camille Maillard in 1912, is a complex series of simultaneous reactions which occur between protein and sugar molecules in the presence of heat, that results in browning of the food and development of new aromatic and flavouring compounds.

Sugar is one of the main participants in this reaction, but not every kind of sugar works. Some sugars like sucrose (a.k.a table sugar) are too complex to react with protein molecules. This kind of reaction requires ‘reducing sugars’. Reducing sugars are simple sugars which can act as reducing agents in such biochemical processes because they have free aldehyde or ketone group.

To decipher this scientific jargon, consider that Sugars are like humans and just like every other human, they live according to the rules of our society. ‘Non-Reducing Sugar’ is a human that is in a relationship and is not free to pursue anyone else. ‘Reducing Sugar’ on the other hand is someone who is single and not tied down by any relationship. They are free to attract ‘Proteins’.

In the Maillard reaction, when you apply heat to the food, it creates a perfect environment for these ‘reducing sugars’ and ‘proteins’ to get together and bond and mix with each other. As a result, these molecules change, evolve and lead to the development of new flavourful, colourful molecules that are responsible for the brown colour and a unique aroma.

How Maillard Reaction affects the colour of Kulfi?

Milk, the major ingredient of Kulfi, already has two main elements that participate in the Maillard reaction, protein and reducing sugar called lactose, naturally present within itself. So when you apply heat for a long duration to the milk, the water molecules start to evaporate and milk starts to concentrate. Concentrating of milk brings these protein and sugar molecules together and starts the series of reactions between them. After a few hours, the result is a fragrant, light brown liquid - a clear indicator that Maillard reaction has occurred.

Even though the Maillard reaction is the main phenomenon that occurs in the kulfi making process, it is important to note that it is not the only reaction that can take place during the heating of the mix.  Sucrose (a.k.a table sugar) being a non-reducing sugar may not be able to participate in Maillard reaction  but it is involved in caramelization reaction. [Caramelization is another process involving sugar molecules that leads to browning of the food.] It depends on how much table sugar (a.k.a sucrose) you add to the mix and when you add it that will determine the degree to which kulfi experiences caramelization reactions.