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The Science of Jasmine Rice

The first time I tasted jasmine rice — in America — I wondered, “What’s the big deal? It tastes like plain rice.”

Not that I ate much rice. My parents were hard-core “meat and potatoes” people. My first wife, a Texan, kept a rarely-used tupper of jasmine rice in our pantry for years. According to a study conducted at Utah’s Brigham Young University, fully-milled rice — if stored in a cool, dry place — can remain edible for decades. In our 30 years of happy marriage, my wife did her best to prove that study right.

When she passed away in 2012, I decided to see the world slowly. After a year in each of Australia and Thailand, I met my second wife in Cambodia...and that’s when my third love affair, with “new crop” jasmine rice, began.

Why “new crop”? Because jasmine rice is seasonal. In typical packaging and storage conditions, its unique and enchanting aroma decline by half before it even reaches America... but, I get ahead of myself. Let’s start at the beginning.

History & Genetics

All Asian rice varieties belong to a single species, Oryza sativa, first domesticated in China around 13,000 years ago (give or take a few millennia). As rice cultivation spread across Asia, local farmers selected among naturally-occurring mutations for flavor, high production, disease resistance, adaptation to local climate and soils, and other desirable traits. Today, the International Rice Research Institute’s Gene Bank stores more than 100,000 different varieties.

One trait shared by all rice varieties is the betaine aldehyde dehydrogenase gene, BADH. When a rice is stressed by drought, flooding, pests, salt, etc., the plant’s BADH gene helps regulate the production of chemical compounds that help it survive — just as your body, when surprised, produces adrenaline.

Thousands of years ago, a natural mutation in rice’s BADH gene created a variation — an “allele” — called badh2.1. When a rice plant with the badh2.1 allele is stressed, it doesn’t produce the normal stress-response compounds; instead, it produces 2-acetyl-1-pyrroline, abbreviated 2AP.

On the one hand, 2AP is useless in responding to stress, which weakens the rice plant. On the other hand, 2AP gives rice an enchanting flavor and fragrance. Over the millennia, traditional farmers have selected for, hybridized, and back-crossed the badh2.1 allele to produce hundreds of locally-optimized varieties of “aromatic rice.” When you experience “harvest-fresh” jasmine rice for the first time, you’ll understand why they went to all of this trouble: it smells and tastes fantastic.

Many other natural mutations also affect the BADH gene, thereby also affecting the aromatic flavor and fragrance of jasmine rice. Some influence 2AP; others influence the production of other, less-well-studied aromatic compounds. Together, these compounds give jasmine rice a rich, complex, and subtle aromatic profile, comparable (in complexity) to coffee, wine, and natural vanilla.

It is important to recognize that all of these aromatic rice varieties occur within a single species, Oryza sativa, and that have been produced entirely by traditional means. It’s like the old joke:

(I said it was an old joke, not a good joke.)

Like different dog breeds, all of the different rice varieties are just “breeds” of a single species, carefully bred by local farmers over thousands of years to meet their local needs (and, in the last hundred years or so, the needs of export markets). According to the International Rice Research Institute, “Currently, no varieties of genetically modified (GM) rice are grown commercially in the world, although several have been approved for commercialization.”

(AwardBest™ rice is 100% GMO-free.)

White and Brown Rice

The animated GIF below (from Wikipedia) shows the different parts of the rice grain.

Rice Animation.gif
"Rice Animation" by Namazu-tron - Self drawing. Licensed under Public Domain via Commons.

"White rice" is rice from which the bran has been milled away (image E in the animation above).

"Brown rice" is rice with the bran mostly intact (image B in the animation above).

The bran contains lots of nutritious substances, so why remove it? Because brown rice spoils much faster than white rice, especially in the heat and humidity of the tropics, where most rice is grown.

As a result, most people from rice-eating cultures grew up eating white rice, and still prefer it.

Quality vs. Quantity

Three main factors affect the quality of jasmine rice: variety, location, and stress.


If you give a young rice plant all of the water, fertilizer, minerals, and sunlight it needs, while keeping it free from pests, weeds, and salt, it will lead a stress-free life. Most modern research has been focused on producing rice varieties that produce the highest possible “yield” of rice grains per acre under such stress-free conditions. Modern methods also tend to focus on using synthetic fertilizers and pesticides to keep the rice plants stress-free, thereby further increasing yield.

However, aromatic rice plants need stress to stimulate the production of 2AP. The more stress, the more 2AP; the less stress, the less 2AP. In science-speak, there’s a “highly significant negative association between aroma and grain yield” (see Kibria 2008 and Wilkie 2004). This is not surprising, given that the 2AP-controlling mutation affects a stress-response gene.

This produces a direct trade-off between quality and quantity. In a given rice paddy, a farmer can either grow a high yield of low-aroma jasmine rice, or a low yield of high-aroma rice — but not both.

Anyone who is familiar with the production of fine wines will recognize this trade-off. Great wines require grapes that are highly stressed by infertile soils, limited water, and vicious pruning. Without such stresses, one could produce a lot more grapes, but the wine made from them would be boringly plain old white rice.


In real estate, the three most important factors are “location, location, and location.”

In winemaking, the French word terroir “incorporates everything that contributes to the distinctive character of a particular vineyard site:  its soil and subsoil; its drainage, slope and elevation; and its microclimate, which in turn includes temperature and precipitation, exposure to the sun, wind and fog, and the like.”

In jasmine rice, location is equally important. Each village’s farmers have worked for centuries to breed the best possible varieties for their particular terroir (with “best” defined to mean “best tasting,” not necessarily “highest-yielding”). Growing those rice varieties in other terroir usually produces rice of inferior quality. Adding irrigation, fertilizer, and pesticides to a “misplaced” variety just makes a bad thing worse.

For example, Thailand’s Khao Kao Dawk Mali (KDML105), is known to produce the best rice when grown in its native Issan, in Thailand’s north-east. Likewise, Cambodia’s Phka Rumduol™ produces the best rice when grown in its native Battambang province. The fact that Issan and Battambang are adjacent is no surprise. Together, they are the homeland of jasmine rice, over which the two neighboring nations, Thailand and Cambodia respectively, have been fighting for centuries.

Which brings me to…


The two jasmine rice “varieties” that have dominated the international market and The World’s Best Rice™ competition (held annually since 2009 by The Rice Trader™, a rice industry consultancy) are Thai Jasmine Rice and Cambodian Jasmine Rice.

      2009 2010 2011 2012 2013 2014 2015
Thai Jasmine Rice     Won Won Tied ?
Cambodian Jasmine Rice     Tied Won Tied ?


It should be noted that:

The 100% success rate of Cambodian Jasmine Rice suggests that is indeed — as the name of the competition suggests — “The World’s Best Rice.” This has been recognized by Thai authorities, including Mr. Chookiat Ophaswongse, honorary president of the Thai Rice Exporters Association, who stated after Thailand and Cambodia’s 2014 tie, “Honestly, Cambodian fragrant jasmine rice nowadays, the quality is somehow better than Thai.”

“Thai Hom Mali Rice” (often Anglicized to “Thai Jasmine Rice”) and “Cambodian Jasmine Rice” are not the names of individual rice varieties. Instead, they are collective brand names, used to describe a collection of varieties which have been chosen by controller of the collective brand name.

The name “Thai Hom Mali Rice” (often expressed as “Thai Jasmine Rice”) is controlled by Thailand’s National Bureau of Agricultural Commodity and Food Standards, which issued its latest standard in 2003. It includes two varieties:

Both varieties are “photoperiod sensitive,” which means that they can only ripen in the Autumn (around November). "Non-photoperiod sensitive" varieties can ripen at any time of year.

Likewise, the name “Cambodian Jasmine Rice” does not refer to a specific rice variety, but rather to a collection of varieties, as defined by the Cambodian Rice Federation (CRF). However, I’m writing this in mid-October 2015, and the CRF is not expected to announce its branding criteria until early November. One variety sure to be included is Phka Rumduol, which is the variety that has won under the “Cambodian Jasmine Rice” name.

Thailand’s Khao Kao Dawk Mali 105 (KDML105) and Cambodia’s Phka Rumduol are genetically distinct varieties, but they are similar in that they produce only one crop per year, in the Autumn, and take four months (or more) to mature.

There are other varieties of jasmine rice that can ripen at any time of year, and which mature in just three months. While they are aromatic (or they wouldn’t be “jasmine rice”), they don’t have as good a flavor, fragrance, or tenderness as the longer-maturing, Autumn-crop-only varieties.

Which brings me to another element of jasmine rice quality: age.


The concentration of aromatic compounds in jasmine rice declines very rapidly after harvesting. Within just a few months, it hardly aromatic at all.

2AP Concentration in jasmine rice

Different scientific studies have different results due to their different storage temperatures, packaging, degree of milling, etc, but they all agree that 2AP content drops like a rock after harvest. The decline in 2AP concentration — in approximate fractions, assuming typical packaging and storage conditions — is 25% (1/4) after the first month, 50% (1/2) after the second month, 67% (2/3) after the third month, and 80% (4/5) after the six month.

It is not clear from these studies whether 2AP content continues to decline after the sixth month — by which time more than 80% of its harvest-fresh 2AP is already gone — or if it continues to decline thereafter.

In any case, in typical packaging, shipping, and storage conditions, by the time jasmine rice reaches America from Asia — two or three months after harvest — the enchanting flavor and fragrance for which you’re paying a premium has already declined by somewhere between half and two-thirds.

That’s why my first wife’s tupper of many-years-old jasmine rice tasted like “plain white rice.” By the time I first tasted it, all of its enchanting, beguiling, delightful aromatics were long gone. It wasn’t “aromatic rice” anymore...except in the eyes of the US Department of Agriculture, which defines “aromatic rice” as “special varieties of rice (Oryza sativa L. scented) that have a distinctive and characteristic aroma; e.g., basmati and jasmine rice” (US Standards for Rice, §868.315(f)). That is, the USDA defines “aromatic rice” by its genetics, not by whether it actually has any aromatic compounds left in it. That’s similar to the Thai standard, which uses the phrase “depending on age” to make the same point.

Age also has an equal but opposite effect: while the “good” aromatics such as 2AP are declining, “bad” smelling aromatics — with names like “cardboard” and “sewer animal” — increase with age. Washing the rice thoroughly, and rinsing it until the rinse water runs clean, can remove most of these bad aromatics — but no amount of washing can put back the “good” aromatics that are already gone.

Many studies have explored ways of slowing or stopping this rapid decline in quality (notably Goufo 2010, Tananuwong 2010, and Yoshihashi 2005). These studies have shown that special packaging materials, such as those used for specialty coffee, don’t help much. Neither does vacuum-packing (although it slows the accumulation of bad smells).


The only thing that’s been definitively proven to keep jasmine rice “harvest fresh” is temperature reduction — that is, refrigeration. The colder the storage temperature, the slower the loss of “good” aromatics, and the slower the accumulation of “bad” aromatics.

This is no surprise. Temperature is a measure of energy — the same energy that is used in biological and chemical reactions. Reducing the temperature reduces the amount of energy available for any and all such reactions.

As just one example, the melting point of 2AP is 66°F (19°C). Above that temperature, 2AP is a liquid; below that temperature, 2AP is a solid. In either state, 2AP is highly volatile, meaning that its molecules don’t need much energy to leap away from the rice grain. However, leaping from the solid state (sublimating) requires more energy than leaping from the liquid state (evaporating). Therefore, stored rice loses 2AP much more slowly at 65°F (solid) than at 67°F (liquid), all else being equal.

Some of jasmine rice’s other aromatic compounds have higher melting points than 2AP’s; some have lower. As rice’s storage temperature is reduced:

Similarly, as the temperature is reduced, the energy available for the reactions that produce “bad” aromatics (by oxidation, hydrolyzation, and rancidification) declines.


The scientific studies that have investigated refrigerating rice — but not freezing it — have had mixed results. However, the studies that have investigated freezing rice are unanimous: freezing retains “good” aromatics, and prevents the “bad” aromatics from forming.

Water is, in effect, just another volatile compound (H2O). As rice grains age, water molecules leap away from the rice grain — just as 2AP does — drying and hardening the rice grains.

“Freezing” is nothing more than “reducing the temperature below the melting point of water,” which is 32°F (0°C). “Deep freezing” is lowering the temperature much lower, to -4°F (-20°C). You could freeze rice even colder — by storing it in liquid nitrogen, for example — but the benefits of doing so are quite small. Taste-testing panels have found that deep-freezing at -4°F (-20°C) preserves the “good” fragrances of fresh jasmine rice, while preventing the “bad” smells from accumulating. One might characterize these result by saying that deep-freezing maintains rice’s “harvest-fresh” flavor and fragrance.

However, there’s a problem with freezing. If rice is frozen slowly, the water has time to form ice crystals that can pierce the rice grain’s cell walls, making it mushy when cooked. Clarence Birdseye solved this problem back in the 1920’s with the invention of quick-freezing. Quick freezing happens so quickly that ice crystals don’t have time to grow, so the rice isn’t mushy. (More details on modern quick-freezing here.)

You’ve seen this before, with frozen peas. Fresh peas that are quick-frozen in the field — within an hour or two of being picked — have better flavor and nutrition than the never-frozen “fresh” peas that have taken days or weeks to reach your neighborhood supermarket. Similarly, quick-freezing, followed by storage at deep-freeze temperatures, can maintain jasmine rice’s “harvest-fresh” flavor, fragrance, and nutrition.

How long can freezing maintain the “harvest-fresh” quality of jasmine rice? Not scientific studies have looked at this question for storage periods longer than a year. At the end of that year, tasting panels determined that the quality of deep-frozen rice had not declined significantly, so the answer seems to be: many years.

Options to Address the Problem of Aging in Jasmine Rice

Clearly, the “quality” option is to quick-freeze jasmine rice and to keep it frozen until the customer buys it. However, that’s expensive, and the global market for jasmine rice is a high-volume, price-sensitive commodity market. (The only source of quick-frozen, deep-frozen-stored jasmine rice in the world today, so far as I know, is my new company, AwardBest.)

The “cheap” option is blending. The blender takes high-quality (but aging) jasmine rice, and mixes in some inferior (but fragrant) fast-growing, any-season variety that has been harvested more recently. The result is rice that tastes and smells...kinda sorta jasmine-y, more or less, if you don’t know what you’re missing, which most Americans don’t. It’s somewhere between OK and meh. But it’s cheap, and there’s always a market for cheap.

One last option is to think of jasmine rice as being seasonal.  This is how it’s treated in Southeast Asia, where soaring tropical temperatures and high electricity costs make freezing or refrigerating rice unaffordable. There, and in the diaspora communities of Southeast Asians worldwide, the knowledgeable locals seek out the “new crop” of top-quality jasmine rice each Autumn, and enjoy the heck out of it while it lasts...and then go back to eating whatever.

If you look for “new crop” rice, remember that the best varieties — such as Phka Rumduol — are harvested in November, and reach America in January or February — of the next year. So, in 2016, look for “New Crop 2015”, not 2016.

Peer Review

This is not a scientific paper. However, as its deadline approached, I wanted to make sure that I was getting the facts straight. Therefore, I asked a couple of its cited scientists to review the paper to see if I'd made any material errors. Dr. Goufo and Dr. Wilkie were kind enough to review it and to give me permission to quote them as saying that it was an accurate summary of the current scientific literature on the topic, as simplified for a non-technical audience. Nonetheless, if you find any factual errors in it, or know of any new research in the area that I should consider including in updates to this article, please let me know at

Next Up: The Science of Cooking Jasmine Rice

This article is already more than 3000 words long, so I’m going to stop here. I will eventually publish a second article in “The Science Of…” series, which will cover selecting, preparing, and cooking jasmine rice.

In Conclusion

Despite my new love affair with jasmine rice, I still enjoy meat and potatoes. Even in my new wife’s rural Cambodian village, I’ve been known to prepare a burger and fries. However, these days, I eat a lot of rice.

I’m really looking forward to next month’s “New Crop 2015” of the Phka Rumduol variety of Cambodian Jasmine Rice, and — since you’ve read this far — I hope that you are, too.