Processing Pulses: From Raw Legumes to Edible Delights

Pulses are among the most important food crops in the world, providing essential protein and nutrients to billions of people. However, raw pulses are rarely consumed directly-they must undergo various processing steps to become edible, digestible, and nutritionally optimized. Understanding how pulses are transformed from raw legumes to the diverse range of products we enjoy daily reveals a fascinating intersection of traditional knowledge and modern food science.

What is pulse processing? 🔗

Pulse processing refers to the series of operations that convert raw pulse grains into consumable forms. Pulses are often consumed after dehusking and splitting, typically as dehusked splits known as dal, which improves their culinary properties and reduces antinutritional factors. The presence of gummy substances between the seed coat and cotyledons makes husk removal challenging, requiring various pre-milling treatments to loosen the seed coat before milling.

The processing journey involves three distinct levels: primary processing (cleaning and grading), secondary processing (dehusking and splitting), and tertiary processing (creating value-added products). Each stage serves specific purposes in enhancing edibility, improving nutritional value, and extending shelf life.

Primary processing: cleaning and grading 🔗

The first stage in pulse processing focuses on preparing raw pulses for further operations. This step is crucial because unprocessed pulses contain various impurities that must be removed before consumption or subsequent processing.

Cleaning operations 🔗

Cleaning removes dust, chaff, dirt, stones, damaged seeds, weed seeds, and immature grains from the pulse lot. Modern processing plants use multiple cleaning stages including pre-cleaners, destoner separators, and gravity separators to achieve thorough purification. Air-screen separators, vibratory sifters, and optical color sorters help detect and remove discolored, split, or damaged pulses.

Grading operations 🔗

After cleaning, pulses are graded according to size using reel-type or rotating sieve-type cleaners. Grading ensures uniform processing in subsequent steps and helps achieve consistent quality in the final product. Indented cylinder separators classify pulses based on length and size, while gravity separators ensure precise separation based on density.

Secondary processing: dehusking and splitting 🔗

Secondary processing transforms whole pulses into the dehusked splits (dal) that form the basis of countless dishes. This stage involves several interconnected operations that require careful handling to maximize yield.

Pre-milling treatments 🔗

Before dehusking can occur, the husk must be loosened from the cotyledon. Various processing techniques such as heating, milling, dehulling, soaking, sprouting, fermentation, and cooking are employed for this purpose. Two primary methods exist:

Wet milling method: Cleaned pulses are soaked in water for 4-12 hours, then mixed with red earth for 12-16 hours before sun drying to achieve approximately 10-12% moisture content. The red earth imparts a yellow colour to the final product and helps remove small patches of adhering husk through its mild abrasive quality.

Dry milling method: Pulses are passed through roller dehuskers where scratches, dents, and cracks form on the outer seed coat. Oil is then applied to the surface (typically 150-250g per 100kg of pulses), and the pulses are stored for one to three days to allow oil penetration between husk and cotyledon.

Dehusking and splitting process 🔗

For dehusking conditioned pulses, carborundum-coated emery rollers are used. In a single pass, approximately 50% of pulses are dehusked and split into two parts. The dehusked splits are separated by sieving while the husk is removed through aspiration. Unsplit dehusked pulses undergo repeated processing until complete dehusking and splitting is achieved-typically requiring two to three cycles.

Traditional mills achieve yields of only 65-75% compared to the potential yield of 82-85% due to losses from excessive abrasive force that creates brokens and powder. Modern processing methods have improved this to 78-80% yield with fewer broken pieces.

Polishing 🔗

The final step in secondary processing involves polishing the dehusked splits with small quantities of oil and/or water. This enhances the appearance and surface quality of the dal, making it more appealing to consumers.

Tertiary processing: value-added products 🔗

Tertiary processing transforms basic dal into a wide variety of products that cater to diverse culinary applications. These processes not only create versatile ingredients but often improve nutritional quality by reducing antinutritional factors.

Besan (gram flour) 🔗

Besan or gram flour is a pulse flour made from chana dal or split Bengal gram. It contains a high proportion of carbohydrates, higher fiber relative to other flours, no gluten, and a higher proportion of protein than other flours. This versatile flour is a staple in South Asian cuisines, used for making pakoras, chilla (pancakes), laddu, and numerous other dishes. In Mediterranean cuisines, similar chickpea flour is used for farinata in Italy and socca in France.

The production of besan involves grinding dehusked pulses into fine powder using plate mills, roller mills, or hammer mills. The process removes the outer hull while preserving the nutrient-rich cotyledon, resulting in a flour that serves as an excellent binding agent, thickener, and primary ingredient in both savory and sweet preparations.

Roasted and puffed products 🔗

Processing pulses through puffing, flaking, and milling into flour can improve their nutritive value by reducing anti-nutritional factors. Puffing exposes grains to high steam pressure which causes them to burst open and expand in size. Flaking involves partially cooking grains through steaming then pressing them into thin crispy flakes. These techniques increase protein, fiber, and mineral content while decreasing compounds responsible for flatulence.

Fermented products: dosa and idli 🔗

Among the most celebrated pulse-based products are the fermented foods idli and dosa, which represent an ingenious combination of cereals and legumes. Idli is a traditional fermented rice and black gram based food prepared by soaking rice and decorticated black gram, grinding them separately, mixing the batters with salt, and allowing fermentation overnight.

Traditional fermented foods like idli and dosa deliver a balanced diet of both carbohydrates and proteins. Lactic acid bacteria and yeasts facilitate the fermentation process, which enhances nutritional value and shelf life. The combination of rice and black gram creates a complete protein containing all essential amino acids.

Nutritional improvements through processing 🔗

Processing does more than make pulses edible-it significantly enhances their nutritional profile. During fermentation of idli batter, vitamins B and C increase while phytate is hydrolyzed by almost 50%. The vitamin content of fermented idli batter reaches approximately 0.59 mg riboflavin, 0.59 mg thiamine, and 0.76 mg folic acid per 100 grams.

Reduction of antinutritional factors 🔗

Raw pulses contain several compounds that can interfere with nutrient absorption, including trypsin inhibitors, phytates, lectins, and tannins. Pulses must be pretreated using process combinations such as soaking, dehulling, cooking, fermentation, germination, and extrusion to reduce these antinutritional factors.

Dehulling effectively reduces tannins, saponins, and total phenolics. However, it may increase the relative concentration of phytic acid and enzyme inhibitors since these compounds are more concentrated in the cotyledon than the hull. Therefore, combining dehulling with other treatments like soaking, cooking, or fermentation provides optimal results.

Improved digestibility 🔗

Processing breaks down complex proteins and starches, making them more accessible to digestive enzymes. Fermentation produces beneficial probiotics that help maintain a healthy balance of gut bacteria. These probiotics improve digestion, enhance nutrient absorption, and support the body’s immune defenses. The proteins from black gram in fermented products become easily digestible, providing building blocks for tissue repair and enzyme production.

Common pulse products and their applications 🔗

The processing of pulses yields numerous products integral to global cuisines:

Dals: Dehusked and split pulses form the foundation of countless dishes. Arhar dal (split pigeon peas), moong dal (split green gram), urad dal (split black gram), and masoor dal (split red lentils) each offer distinct flavors and cooking properties.

Besan-based preparations: From savory snacks like bhujia and sev to sweet treats like besan laddu, gram flour demonstrates remarkable versatility. It serves as a binding agent in vegetable fritters, a coating for fried foods, and a thickening agent in curries.

Fermented breakfast items: Idli and dosa remain staples in South Indian cuisine, consumed by millions daily. Their light texture, easy digestibility, and nutritional completeness make them suitable for people of all ages, including infants and those recovering from illness.

Extruded snacks: Modern extrusion technology creates pulse-based snacks with improved texture and extended shelf life. These products combine the nutritional benefits of pulses with the convenience and appeal of ready-to-eat snacks.

The science behind traditional processing wisdom 🔗

Many traditional pulse processing methods have been validated by modern science. The practice of soaking pulses before cooking, for instance, activates enzymes that break down antinutritional factors. Similarly, fermenting rice and pulse batters creates conditions where beneficial bacteria thrive, producing organic acids that further enhance nutritional bioavailability.

The combination of cereals and pulses in dishes like idli represents nutritional complementation-cereals provide amino acids that pulses lack, and vice versa, resulting in a complete protein profile. This traditional knowledge, developed over centuries, aligns perfectly with modern nutritional understanding.

What do you think? How might modern food technology further improve traditional pulse processing methods while preserving their nutritional and cultural significance? What role could pulse-based products play in addressing global protein needs sustainably?

References

1. https://www.sciencedirect.com/science/article/abs/pii/B978044318965400011X
2. https://www.frontiersin.org/journals/sustainable-food-systems/articles/10.3389/fsufs.2021.681662/full
3. https://onlinelibrary.wiley.com/doi/full/10.1002/leg3.111
4. https://en.wikipedia.org/wiki/Gram_flour
5. https://www.slideshare.net/slideshow/antinutritional-factors-in-pulses/246413104
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC3551127/
7. https://www.taylorfrancis.com/chapters/edit/10.1201/9780429274787-12/nutritional-health-benefits-idli-dosa-srinivasan-ramalingam-sujatha-kandasamy-ashutosh-bahuguna-myunghee-kim
8. https://pubmed.ncbi.nlm.nih.gov/34324249/
9. https://continentalhospitals.com/blog/can-idlis-and-dosas-improve-your-gut-health/