The Science Behind Manufacturing Khoa, Rabri, and Basundi

Khoa, Rabri, and Basundi are three of India’s most cherished heat-desiccated dairy products. They share a common foundation – the controlled evaporation of moisture from milk through continuous boiling – yet each one has a distinct manufacturing approach that gives it a unique texture, flavour, and culinary identity. Together, they form the backbone of India’s traditional sweet-making industry, with approximately 1.5 million tonnes of khoa alone produced annually in India. Let’s break down the science and process behind how each of these products is made.

What is milk desiccation and why does it matter? 🔗

At its core, the manufacture of Khoa, Rabri, and Basundi relies on a single principle: milk desiccation. This means removing water from milk by applying heat, which concentrates the milk solids – fat, protein, lactose, and minerals – into a thicker, richer product.

Fresh milk contains about 87% water. Through continuous boiling and evaporation, this water is driven off until the desired level of total solids is reached. For Khoa, the target is typically 65-72% total solids. For Rabri and Basundi, the concentration is less intense, resulting in products that retain more moisture and have a flowing or semi-liquid consistency.

During this concentration process, important chemical changes occur. The Maillard reaction – a series of reactions between milk proteins and lactose – produces the characteristic light brown colour and caramelised flavour found in these products. Proteins also denature and form new bonds, contributing to the body and texture of the final product.

Principle of Khoa manufacture 🔗

Khoa (also known as Khoya, Mawa, or Kava) is the most concentrated of the three products. It is a partially dehydrated milk product that serves as the base ingredient for dozens of Indian sweets, including burfi, peda, gulabjamun, and kalakand.

The traditional method 🔗

Traditionally, Khoa is prepared by boiling 2-3 kg of milk in an open, wide-mouthed iron pan called a karahi, placed over a non-smoky fire. The milk is stirred continuously in a circular motion using a flat-ended iron stirrer (khunti). Throughout the operation, all surfaces of the pan that come in contact with milk are lightly scraped to prevent milk solids from sticking and burning.

As moisture evaporates progressively, the milk thickens. At a certain stage, the mass shows an abrupt change of colour – this indicates heat coagulation of milk proteins. Vigorous stirring and desiccation continue until the product reaches a pasty consistency and begins to leave the sides of the pan. The final Khoa pat is shaped after removing the pan from the fire.

Three types of Khoa 🔗

Khoa is classified into three varieties – Pindi, Danedar, and Dhap – each with specific characteristics and end uses:

Pindi Khoa has the highest total solids content (minimum 65%) among all variants. It has a smooth, homogeneous body and is shaped into circular balls or hemispherical pats. Pindi is the preferred base for sweets like burfi and peda, where a firm, smooth texture is essential. During its final stage, the product is vigorously worked against the walls of the pan using a wooden ladle to achieve that smooth consistency.

Danedar Khoa has a distinctly granular texture. This granularity is achieved by adding a small amount of acidulant – usually citric acid at around 0.02% – during the initial boiling stage. The acid triggers early coagulation of milk proteins, forming grains that grow in size as the milk concentrates. This type is ideal for products like kalakand and milk cake, where a grainy texture is valued.

Dhap Khoa (also called Kaccha Mawa) retains the highest moisture content of the three types. It has a loose, sticky body and smooth texture. This extra moisture makes it easy to mix with other ingredients, which is why Dhap is the preferred variety for making gulabjamun, kalajamun, and carrot halwa.

As per Food Safety and Standards Regulations (FSSAI, 2011), Khoa must contain a minimum of 30% milk fat on a dry weight basis and must be free from added starch, sugar, and artificial colouring. Up to 0.1% citric acid is permitted (primarily for the Danedar variety).

Principle of Rabri manufacture 🔗

Rabri is a sweetened, concentrated whole milk product characterised by several layers of clotted cream (malai) dispersed in thickened, sweetened milk. It is one of the most popular milk desserts in northern and eastern India, especially during festivals.

How Rabri differs from Khoa 🔗

While Khoa involves continuous stirring throughout the boiling process, Rabri production takes the opposite approach in its early stages. The milk is heated to simmering temperature (85-90°C) and maintained there with controlled, gentle heat – without stirring. This allows a skin or pellicle (malai) to form on the surface of the milk.

Step-by-step process 🔗

Buffalo milk is normally used for Rabri due to its higher total solids and superior taste in the final product. The milk is poured into a wide-mouthed karahi and brought to a simmer. As the surface heats, fat and protein rise and form a thin film. This film is gently pushed to the cooler sides of the karahi using a khunti (flat scraper), where it solidifies into a cream layer.

This process of film formation and collection is repeated multiple times – roughly every 10 minutes – until no more skin forms. Meanwhile, the milk continues to evaporate and concentrate. Once the milk has reduced sufficiently, sugar (about 6% of the original milk weight) is added and dissolved. The collected malai layers are then folded back into the concentrated milk and mixed gently. Flavouring agents like cardamom, saffron, or nuts may be added at this stage.

The result is a rich dessert with approximately 30% moisture, 20% fat, 10% protein, and 20% added sugar. Because Rabri contains all the milk solids in roughly a five-fold concentration plus sugar, its nutritive value is very high.

The critical skill in Rabri-making lies in managing the heat so that the milk simmers without vigorous boiling. If the temperature is too high, the skin won’t form properly; if too low, the process takes excessively long, increasing the risk of microbial contamination.

Principle of Basundi manufacture 🔗

Basundi is a heat-desiccated, thickened milk dessert popular in western and southern India, particularly in Maharashtra, Gujarat, Karnataka, and Tamil Nadu. It has a white to light caramel colour, creamy consistency with soft-textured flakes suspended throughout.

How Basundi differs from Rabri 🔗

Basundi and Rabri are often confused, but there are key differences. Rabri has distinct, hard flaky layers of clotted cream, whereas Basundi is generally more homogeneous with very fine, soft flakes. Basundi is concentrated to about two-fold (approximately 49-57% total solids), while Rabri achieves a higher concentration. Basundi also tends to have a more pronounced caramel flavour due to its slightly longer, gentler heating process.

The manufacturing process 🔗

Buffalo milk is preferred for Basundi as well, owing to its high total solids. The milk is heated in a shallow karahi over gentle fire. Unlike Rabri, the milk in Basundi preparation undergoes occasional scraping at the bottom while being thickened through evaporative heating. A thin skin forms on the surface periodically, and this is removed using a khunti and set on the cooler sides at the top of the karahi.

As boiling continues, more skin forms and is collected. When the milk reaches a consistency similar to condensed milk, sugar (about 15-17% of the concentrated milk) is stirred in until fully dissolved. The karahi is then removed from the fire, and flavouring materials – powdered cardamom, saffron, and sometimes edible camphor (each at about 0.02% of concentrated milk) – are added and mixed.

The finished product has a pleasant caramelised flavour and thick, pourable consistency. It is typically served chilled. The total annual production of Basundi in India is estimated at around 25,000 tonnes, and it remains largely a cottage-scale product.

Role of heat source in product quality 🔗

The choice of fuel significantly affects the final product’s flavour and texture. Traditionally, wood and coal were the primary heat sources. Wood-fired heating lends a subtle smoky character to the product that many consumers associate with authentic taste. However, these fuels demand constant monitoring to maintain even temperature, and using smoky fuel is a common cause of off-flavour defects in Khoa.

In modern production settings, LPG (liquefied petroleum gas) and steam have largely replaced solid fuels. LPG offers clean, adjustable heat that reduces the risk of scorching. Steam-jacketed kettles provide the most precise temperature control and are standard equipment in organised dairy plants. This consistency is especially important in commercial-scale production, where uniform product quality across batches is essential.

The role of agitation and scraping 🔗

Proper stirring and surface scraping serve multiple critical functions during manufacture. First, scraping prevents milk solids from depositing on the heated pan surface and charring, which would introduce burnt particles and off-flavours. Second, stirring ensures uniform heat distribution throughout the milk, so all portions of the liquid concentrate evenly. Third, the mechanical action of scraping ruptures fat globule membranes, releasing free fat – khoa typically contains about 60% of its total fat as free fat, which contributes significantly to its rich mouthfeel and smooth texture.

The intensity and pattern of stirring also determine the type of product. Continuous vigorous stirring yields the smooth Pindi Khoa. Intermittent or no stirring (as in Rabri) allows cream layers to form. Occasional gentle scraping (as in Basundi) produces soft flakes. This is why the same basic principle – milk desiccation – yields three quite different products.

Mechanised and modern approaches 🔗

While traditional methods remain widespread, mechanised systems have been developed for large-scale production. The National Dairy Development Board (NDDB) at Anand, Gujarat developed the Inclined Scraped Surface Heat Exchanger (ISSHE) for continuous Khoa manufacture. The National Dairy Research Institute (NDRI) at Karnal developed the Thin Film Scraped Surface Heat Exchanger (TSSHE), which arranges two heat exchangers in a cascade – the first concentrates milk to 40-45% total solids, and the second finishes the desiccation.

These machines can produce around 50 kg of Khoa per hour and have been adopted by many organised dairies. Membrane technologies like reverse osmosis (RO) have also been explored, where milk is first pre-concentrated (2.5-fold for cow milk, 1.5-fold for buffalo milk) before being desiccated in a conventional system. This reduces boiling time and energy consumption.

For Rabri and Basundi, mechanised approaches typically involve steam-jacketed stainless-steel kettles with controlled heating zones. Some modern processes use vacuum evaporation for milk concentration followed by skin formation in conventional vessels, combining efficiency with traditional product characteristics.

Key factors that affect product quality 🔗

Several variables influence the quality of the finished product:

Type of milk: Buffalo milk is generally preferred for all three products because of its higher fat and total solids content, which yields a richer, creamier product. Cow milk produces lighter-coloured products with a softer body.

Fat content: Higher fat levels contribute to better flavour, texture, and shelf life. Milk with inadequate fat produces Khoa with a hard, dry body.

Acidity of milk: Fresh, sweet milk with low acidity is essential for Pindi Khoa. For Danedar Khoa, slightly acidic milk or controlled acid addition produces the desired granularity. Excessively acidic milk causes sourness in the final product.

Temperature control: Overheating causes scorching and browning defects, while insufficient heat prolongs the process and may compromise safety. Consistent moderate heat is ideal.

Hygiene and storage: Traditional Khoa has a shelf life of only about 5 days at 30°C. Proper handling, packaging, and cold storage are essential to prevent spoilage from yeast and mould growth.

What do you think? How do you see the balance between preserving the artisanal character of these traditional dairy products and adopting mechanised methods for consistency and scale? Is it possible to maintain authentic flavour and texture in an industrial setting?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC10020399/
2. https://www.irjmets.com/uploadedfiles/paper/volume_3/issue_11_november_2021/17211/final/fin_irjmets1637745886.pdf
3. https://www.slideshare.net/slideshow/heat-desiccated-milk-products-process-uses/269845636
4. https://onlinelibrary.wiley.com/doi/10.1111/1471-0307.12266
5. https://www.agrimoon.com/wp-content/uploads/TRADITIONAL-DAIRY-PRODUCTS-1.0.pdf
6. http://ecoursesonline.iasri.res.in/mod/page/view.php?id=148065