A Primer on Parboiling

Just about all rice-eating states will distinguish raw from parboiled rice, with some regions and some communities expressing strong preferences for one or other. But was this always so? This essay on the then-and-now of parboiling has been prepared by Sweta Biswal, with editing, photographic and other inputs by Pratiba Bhat, Sayantani Mahapatra and Deepa Reddy.

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What is Parboiling? | The Process | Beaten rice & Parboiling Origins |
Typing Rice by Parboiling | The Virtues of Each | Improved nutrition & other benefits |
Ayurvedic Thinking on Parboiled Rice | When did Parboiling divide and conquer us? |
Sources & further reading

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What is parboiling?

Parboiling refers to the practice of partially cooking paddy prior to milling. The process is a conditioning technique; it partially gelatinizes the crystalline starch structure of the rice endosperm, making the kernel somewhat hardened and the grain appear translucent. This is an ancient practice of processing the paddy that probably originated in India and then spread through other rice-eating communities, though the precise details of origin and technology dispersal are difficult to trace.

Parboiling as such is not a rice-specific processing technique, nor is its origin exclusive to India. Archeological evidence points to the practice of parboiling wheat to obtain some form of bulgur in Northern Greece towards the end of 3^rd millennium BCE. It is a practice that has merely gained traction with time such that almost a quarter of the paddy produced in the world today is subjected to parboiling. For much of the rice-eating population in South Asia, rice falls into two categories: parboiled being often the choice for everyday cooking, and raw. Interestingly, the word ‘parboil’ comes from the old French word ‘parboillir’ with means ‘to boil thoroughly,’ though we understand it in English as “par-boil,” ‘part’ or ‘partial’ boiling. 

Usually, it is the big/bold non-aromatic grains that are subjected to parboiling. Smaller-grained aromatic rice loses aroma with such processing. Additionally, some rice varieties do not respond well to parboiling: in some cases the boiled/steamed paddy tends to clump and stick together making the subsequent drying process difficult. There are, however, notable exceptions like some Basmati varieties (producing the distinctly yellow-tinted Sella or Sela Basmati) or Macchakanta (a native variety from Odisha) where controlled parboiling is employed to harden the grains just enough to keep them from breaking while being cooked into biryani or pulao. The outer layer of such grains retains their firmness even though the core is fully cooked (soft), adding to the mouthfeel. It is important to note that these varieties are considered commercially important, and the length of the grain is directly proportional to the final price they command.

The Process

While ‘parboiling’ is a generic term applied to soaking, steaming/heating, and then subsequent drying of the paddy before milling, there are wide variations in the process, both when done on smaller scales by households for domestic consumption as well as in industrial processing. Right from the soaking time and temperature of water (and soaking under high pneumatic pressure) to the application of heat to the final drying, each step can be modulated and regulated to influence the final product. For example, soaking at high temperatures induces the reaction of amino acids. and sugars resulting in the browning or yellowing of the rice grain (this is the Maillard reaction)—a process further enhanced during steaming of paddy. This is the method followed for Basmati to produce Sella, or the reason why Sella Basmati is so much more distinctly golden than raw or cold-soaked white-kernel grains.

1. SOAKING: As the first step, the cleaned paddy is soaked in water to saturate the grains. An ideal moisture level is required to fully gelatinize the starch in the caryopsis. If the soaking time is less than ideal, the starch is not gelatinized completely while steeping for too long kick starts the fermentation process and results in a change in the color and smell of the rice.
2. STEAMING: Once the paddy has been thoroughly soaked, it is packed tightly into pots and heated with very little water (steam)/excess water to gelatinize the starch. Usually steaming is preferred over boiling.
3. DRYING: The final drying of the paddy is done in a proper manner to prevent rancidity from developing. Traditionally this was carried out in the shade or partial sunlight in low-temperature conditions that allowed some slow fermentation of the starch which gives parboiled rice its distinctive flavor and culinary appeal. However, at times when a quick turnaround time is important, the parboiled paddy is dried under direct sunlight.

Beaten rice & Parboiling origins

Interestingly, although it appears to be common knowledge that the method and technique of rice-conditioning that we know as “parboiling” may have been developed in India, older texts almost never make reference to the process, let alone describe it. What is commonly mentioned in the texts dealing with dietetics and culinary arts [Pākaśāstra or Pākakalā] is pṛthuka (पृथुक) or “flattened rice”—the technique for preparing which strikes us as having been the most likely precursor to the modern techniques of parboiling. We theorize therefore that contemporary parboiling techniques must have emerged from the historically documented methods of altering rice kernel starch to produce beaten rice–aval, chuda, or poha–and that these are nutritionally similar therefore to parboiled grains.

Consider the following references:  

1. The 300-400 BCE Taittarīyabrāhmaṇa makes reference to lāja and prthuka, puffed rice which looks like a white flower [“lājā vrīhiprabhāvāḥ puṣpavat vikasitāḥ”] and beaten rice, as two rice products used sacrificially [Sreeja p.12]. Preparing for the wedding of Siva to Parvati, Himavat gathers “Mountainous masses of rice, beaten rice [prthuka], jaggery, sugar candies and salt” [Śivapurāṇa 2.3.37: 11].
   • It is unclear in these descriptions what the process of preparing prthuka must have entailed. Paddy could well have been pre-soaked and heated for use in wedding rituals, but not so for more direct sacrifices (homa).
2. The Aṣṭāṅgahṛdaya of Vāgbhaṭa 6.36-37 in 5-600 CE separates the two again but adds their qualities:
   • Lājā (fried paddy) has laghuguna and sita virya. It is indicated to relieve thirst, vomiting, diarrhoea, polyurea, obesity, cough, kapha and pitta dosa. It also acts as digestive stimulant.
   • Prthuka (rice parched and flattened) is having guru guna and gives strength to the body. It also increases kapha and causes constipation. [Prthukā guravo balyāḥ kaphaviṣṭambhakāriṇaḥ]
3. Verses 149-50 of the much later Īśvarasaṃhitā (ईश्वरसंहिता), an 8^th-9^th century Vaisnava āgama text of the Pāñcarātra School which forms the basis for the worship in the Tirunārāyaṇa temple in Melkote, however, suggest a different process:
   • Prthuka is prepared out of sali or grains rent in sali light and heated in the fire along with cooked jaggery. They are to be mixed up with powdered pepper, pieces of jiraka and dried coconut pulp (p.1632-3).
4. Finally, the 17^th century Bhojanakutūhala of Raghunāthasūri drawing on of Vāgbhaṭa specifies that “wet rice grains containing husks are fried. These grains that have not burst open are threshed till they become flat in contour. They are called Prthuka. The grains are heavy, alleviate vata and aggravate kapha. When eaten with milk, they promote growth, are aphrodisiac, impart strength and loosen the stools” [Section 4, on the properties of grassy grains, p35].

Typing rice by parboiling

These textual referents indicate that it all rice can essentially be divided into “raw” and “parboiled,” and that each has their particular quality, value, and utility. Skoda’s 2016 study of Aghria peasant farmers in Western Odisha is useful for explaining the distinction further. He distinguishes RAW or explicitly NOT-parboiled aruā [subdivided into fine-grained aromatic rices and larger grains, used for different purposes]; and two grades of PARBOILED grains: uṣunā and balkā. He provides the character and uses of each for Sambalpuri farmers, which nonetheless correspond to many wider Indian understandings:

In other regions of India, most of the bold varieties of rice (plumper, stouter, hardier grains), which are usually also called ‘coarse’ or ‘rough’ grains because they are grown in rainfed regions (as opposed to irrigated areas, such as river deltas), are grouped as rices to be parboiled. Kerala’s matta rices, Tamil Nadu’s kar rices and Karnataka’s kuchalakki or kusubalakki are examples. Kusubalakki is parboiled rice typically grown in coastal regions and Malenadu. Tamil Nadu’s “kar arisi” is not necessarily parboiled, but is usually a set of bold, red rices like poongar, kullakar and so on, all grown in the kar season (May-June, well ahead of the Samba season). “Palakkadan matta” or “Rosematta” is so-called because it is a red/”rose”-colored, bold variety from Palakkad being parboiled to produce reddish grains. Karnataka’s kuchalakki can be brown or red; the term is not bran color-dependent.

the virtues of rice types

Thus we see how tribal belief systems and mainstream Hindu practice have always accorded a higher status to raw and aromatic rice. Offerings must always be pure and untainted, and hence rice used for ritualistic purposes is always the raw kind. Parboiling, by definition, is twice-cooking and even at times slightly fermented—foods not considered acceptable for offering. By an extension of that rationale, Brahmin communities have a marked predisposition for raw rice in correspondence with the belief that the atman or soul lies within each human, and therefore should be fed only the most untouched of offerings. In erstwhile Zamindari communities, this turns into a preference for ‘fine rice’ encoding class-community behaviour.

The labouring classes, on the other hand, have always favoured the bold parboiled varieties which keep one feeling fuller for a longer time. The quantity of intake is also higher in such population groups as the rice forms the core of their meals. In such a situation, it makes sense to keep costs low. Such distinctions are also reflected in the kind of rice used in preparing pithas, the staple breakfast dishes of Odisha, Bengal, and Assam. The pithas made for ceremonial and ritual offerings are always made with raw rice. But those for regular consumption are generally made from the ‘once parboiled’ type (eksijha or uapakhiya in Odia), or a mix of raw and parboiled types. This is generally true for all communities who can afford to acquire different rices for regular and specialized use.

improved nutrition & other benefits

Parboiled rice grains have a translucent gel-like appearance and are hard as compared to raw rice. They are generally easier to dehusk; milling breakage is reduced, which makes commercial sense. However, there are more advantages to parboiling. The hardening of the grains acts as a deterrent for insects and gives the rice a longer shelf life–many farmers we met parboil for this reason, and because of the market for parboiled as a table rice. The grains retain their firmness and stay discrete even after being fully cooked, yielding a higher volume for the same quantity as compared to raw rice. However, parboiled rice can also be prone to rancidity due to the formation of amylose-lipid complexes and higher concentration of oils in the germplasm. For the same reason, it is sometimes referred to as ‘Teliya chawal’ meaning ‘oily rice’ in parts of India.

Parboiling not only transforms the physical characteristics of the rice grains but also has a marked effect on starch digestibility, the presence of phytic acid (lowered), and the (higher) bioavailability of Iron and Zinc. Parboiling can increase the formation of amylose-lipid complexes in rice, which can increase the amount of resistant starch. This makes the available starch less digestible so the body does not absorb as much of it, resulting in lower Glycemic Load (GL) levels. Parboiled rice was also found to have higher levels of Iron (Fe) as compared to non-parboiled rice due to the tendency of the Fe to diffuse from the outer layer of the rice grain into the endosperm. Even though Zinc (Zn) demonstrates the opposite behaviour, the bioavailability percentage of both the minerals is found to be enhanced when rice is parboiled. [Read more about starches in rice here].

Another big reason for parboiling is the overall reduction in loss, both during milling and cooking. As the starchy endosperm swells up during soaking and partial cooking, it heals the chalky bit and fissures that result in broken grains. And the resulting grains demonstrate more swelling when cooked to the right extent. Also, the grains of parboiled rice do not disintegrate easily even if they are cooked longer than the stipulated time. All these factors also make it economically sensible to adopt parboiling as a regular practice.

At the same time, parboiling introduces a certain uniformity: conditioning rices with heat and water means depletes aroma and some unique elements of taste that raw rice varieties would undoubtedly possess. There is a trade-off, therefore, between keeping the diverse tastes and scents of native rice varieites intact, versus enhancing shelf life and the nutritive value of the starchy endosperm or rice kernel.

Ayurvedic thinking on parboiled riceS

In general, native Indian medicinal systems do not prescribe any single rice type across the board, but will make recommendations based on multiple factors. From this perspective, parboiled rice can be useful but there may be times when it is to be avoided.

The presence of resistant starch or starch acts as though it was part of our dietary fibre, passing into the large intestine and being fermented by gut microbes, makes it seem as though parboiled rice is a panacea: you can eat as much as you like without the same glucose spiking effects as most raw rice, and your gut microbes are fed and happy. But the transfer of too much starch too quickly from intestinal absorption to gut microbiome fermentation can make you a Gassy Gussie—fermentation inherently involves gas production, which can be alright for some with very strong digestive fires, but a symptom of vata buildup for others [source].

As a general rule, bear in mind that parboiled rice (drawing on the Ayurvedic properties of prthuka cited earlier) will have a tendency to alleviate vata and aggravate kapha, but that is not to be taken to mean that it can be consumed in any quantity regardless of body type and work/environmental conditions.

when did parboiling divide and conquer us?

Many rice-eating states in contemporary India will reproduce the typology of Western Odisha—which is to say that for a lot of us, there are two types of rice: raw and parboiled. In Tamil Nadu: pacchai vs. puzhungal. In West Bengal, atop vs. seddho/ siddho chal. In Malayalam: pacchari vs. puzhungalari. And so on. Only in Gujarat, where rice is a marginal staple, is there no concept of parboiling!

This near-universal distinction rules us today—and communities and families are divided over it—but we found no textual precedent for it. This may be because nutrition was once not so important to secure specifically in processing because rice was hand-milled and consumed in very different ways, to maximum nutritional benefit even in its raw forms. The distinction between raw and parboiled that we know now perhaps did not exist in centuries past. But it leaves us with a question: when in our history did parboiled rice become a table-rice of choice?

Many today will proclaim that parboiled rice to be light on the stomach, more filling, and more nutritious. While that is technically correct because scientific studies and experiments have now found that parboiling transforms the starch profile in ways that make it more easily digestible, much depends on individual body types, work and environment, and the way the rice is cooked, stored, and consumed. There is also the question of habit: those accustomed to eating raw polished rice, or raw unpolished rice may find parboiled rice harder to stomach, and even constipating. Conversely, those accustomed to eating parboiled rice complain that raw rice gives them the loosies or runs!

When you hear that parboiled rice is more nutritious than raw rice, remember, however, that this is comparing polished parboiled rice and polished raw rice. If raw rice is eaten unpolished or semi-polished, some of these nutritional differences may not be present or may be less stark. Also keep in mind that some nutritious rices (like njavara, for instance, or dodde baira nellu among many other red and black rices) are eaten only in raw form for specific reasons. It is therefore not quite correct to declare that parboiled rice is universally better than raw rice from a nutritional standpoint. Much depends on context and the realities of the person doing the eating.

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sources & further readings

Primary:

1. Aṣṭāṅgahṛdaya of Vāgbhaṭa, trans. Dr. R. Vidyanath, Varanasi: Chaukhamba Surbharati Prakashan, 2013.
2. Bhojanakutūhala of Raghunāthasūri. Trans. Scholars of the Centre for Theoretical Foundations. Bengaluru, Medplan Conservatory Society, 2019.
3. Īśvarasaṃhitā, Critical Edition vol 5 (Chapters XXIV-XXV) trans. M.A. Lakshmithathachar and V. Varadachari. New Delhi: IGNCA
4. Śivapurāna. Trans. J. L. Shastri Motilal Banarsidass, 2014

Secondary:

1. Awadhesh Kumar, Milan Kumar Lal, Sarangadhar Nayak, Upasana Sahoo, Ajit Behera, Torit Baran Bagchi, C. Parameswaran, Padmini Swain, Srigopal Sharma, “Effect of parboiling on starch digestibility and mineral bioavailability in rice (Oryza sativa L.),” LWT, Volume 156, 2022, https://doi.org/10.1016/j.lwt.2021.113026.
2. Bhattacharya, Kshirod R. “1 – Introduction: rice in historical and social perspectives,” Editor(s): Kshirod R. Bhattacharya, In Woodhead Publishing Series in Food Science, Technology and Nutrition Quality, Woodhead Publishing, 2013, pages 1-25
3. Sreeja K.N. “Dietetics and culinary art in ancient and medieval India A study with special reference to bhojanakutuhala.” Doctoral thesis submitted to the University of Calicut, 2016.  Available online: https://shodhganga.inflibnet.ac.in/handle/10603/145416
4. Skoda, Uwe. 2016. “Rice and Rice Culture: Cultivation and Worship of a Divine Plant in Western Odisha.” In: Roots of Wisdom, Branches of Devotion: Plant Life in South Asian Traditions. Ed. Fabrizio M. Ferrari and Thomas W.P. Dähnhardt. Sheffield: Equinox, pp. 211-240