Pak-kaat-dorng (sweet rice-wash method)

A sweeter form of Thai sour mustard greens

This version of pak-kaat-dorng uses mustard greens, salt, palm sugar and rice-wash water to produce a sour, salty and slightly sweet preserved vegetable.

Instead of kneading the wilted vegetables with a substantial dry-salt addition, this method packs the vegetables in an earthenware vessel and covers them with a liquid prepared from salt, palm sugar, water and rice-wash liquid.

The vessel is closed and exposed to sunlight during fermentation.

The documented period is 3–5 days, shorter than the 5–10 days given for the high-salt version.

The finished product is described as distinctly sour, with both sweetness and saltiness.

Its principal vegetable is mustard greens, Brassica juncea, or a related Chinese mustard vegetable.

The method is a good illustration of how a single Thai preserved-food name can include two fundamentally different microbial environments.

The dry-salted version begins with relatively little free liquid.

This version begins with enough liquid to cover the greens.

That affects salt distribution, substrate availability, oxygen exclusion and the way the final product is eaten.

Historical and regional setting

Pak-kaat-dorng belongs to the extensive family of preserved mustard greens eaten in Thailand and neighboring countries.

Related foods occur under names such as som pak gaat in Laos, Dưa cải chua in Vietnam and sunn cài in Chinese cooking.

The development of these preparations reflects both agricultural availability and the importance of preserved vegetable flavor in rice-based meals.

The precise historical route by which mustard-preservation methods spread across mainland Southeast Asia is not established by the recipe source.

Nor does the presence of rice-wash water prove that this method was developed before the high-salt technique.

The documented recipe appears in the 1995 Thai fermented-food inventory now maintained by JIRCAS.

The recorded method identifies production in small-scale industry and describes culinary uses rather than a particular festival or ritual setting.

It is therefore most accurately presented as a living regional food technology.

Recipe overview

Mustard greens — 2 kg

Salt — 1 cup

Palm sugar — 1 cup

Water — 2 cups

Rice-wash water — 3 cups

Wilting — One day or until wilted

Fermentation — 3–5 days

Environment — Closed earthenware jar exposed to sunlight

Historical keeping claim — 1–2 months

The recorded method does not give a numerical fermentation temperature, water activity or final pH.

Ingredients

Mustard greens or Chinese mustard — 2 kg

Salt — 1 cup

Palm sugar — 1 cup

Water — 2 cups

Rice-wash water — 3 cups

The recorded method permits a mixture of cooked rice and water in place of rice-wash water, but does not give an exact cooked-rice quantity for that substitution.

That missing amount should remain unspecified.

The recipe does not call for vinegar.

Its sourness is intended to develop through the processing and fermentation environment rather than through deliberate addition of a separately prepared acid.

Mustard greens

The vegetable provides the main texture and part of the fermentable substrate.

Thick-stemmed mustard plants are particularly suitable because their leaves soften without immediately destroying all structural integrity.

The leaves and stalks contain water, fiber and carbohydrates, together with compounds characteristic of the mustard family.

Different mustard cultivars can produce noticeably different results.

The original source names Brassica juncea and Chinese mustard under the historical botanical designation Brassica chinensis.

The latter name is associated with a group now generally placed within Brassica rapa.

There is no reason to substitute unrelated leafy greens and assume the same behavior.

Leaf thickness, soluble carbohydrate concentration and tissue structure all affect fermentation.

Salt

Salt is added to the liquid rather than kneaded directly through the vegetable as the primary process.

This changes the way it distributes.

When dissolved, sodium and chloride ions become available throughout the brine, and salt gradually moves into the vegetable tissues.

Some water also moves out of the vegetables as the system approaches equilibrium.

The ingredient list specifies 1 cup salt, but does not specify its weight, crystal size or bulk density.

Consequently, an exact salt percentage by mass cannot be calculated reliably from the cup measure alone.

A cup of coarse salt may weigh substantially less than a cup of fine salt.

The amount is important to preserve exactly in the historical record, but modern process validation would require a defined salt mass and measurement of the finished brine.

Palm sugar

Palm sugar is a traditional sweetener prepared from sap collected from certain palm species.

The precise species used in this Thai recipe is not specified.

Thai palm-sugar production may involve palmyra palm or coconut-palm sources, among others.

Palm sugar contributes sweetness and a more complex aroma than highly refined sucrose alone.

It also adds fermentable carbohydrate once suitable sugars are available in the liquid.

That additional carbohydrate can support acid production by lactic acid bacteria.

The sugar does not automatically make the food safer.

Its effect depends on salt, temperature, the microorganisms present and the rate at which acid accumulates.

In an uncontrolled fermentation, additional sugar may also support undesirable microorganisms.

Rice-wash water

Rice-wash water is the liquid obtained when rice is washed before cooking.

Its composition depends on rice variety, washing method, the amount of rice and the quantity of water.

It can contain suspended starch particles and soluble material released from the grain.

Some traditional methods use a cooked-rice-and-water mixture instead.

Rice-wash water should not be treated as an exact chemical ingredient with a fixed concentration.

One household's washing liquid may contain much more suspended starch than another's.

The important traditional principle is that rice-associated material contributes to the fermentation environment.

However, ordinary lactic acid bacteria cannot all degrade raw starch directly.

The extent to which this addition supplies immediately fermentable sugar depends on the actual carbohydrate composition and microorganisms present.

Equipment

Use a clean earthenware jar or a suitable non-reactive food-grade fermentation vessel.

The recorded method specifies earthenware for this method.

A large washing bowl, clean tray and separate container for dissolving salt and sugar are also required.

If using a modern fermentation vessel, choose a system that allows gas to escape safely while minimizing contamination.

The historical instruction to expose a closed jar to sunlight must not be understood as a validated thermal-control method.

Sunlight can cause large and unpredictable temperature changes.

Method

1. Select and trim the vegetables.

Prepare 2 kg mustard greens, removing defective leaves and damaged parts.

Preserve usable thick stalks and leaves.

The recorded method does not specify whether the weight is measured before or after trimming.

2. Wash thoroughly.

Remove soil from the leaf bases and between overlapping stalks.

Drain excess surface water.

Cleanliness is important because contaminated soil and damaged vegetable material can introduce unwanted microorganisms.

3. Wilt in sunlight.

Spread the cleaned greens in the sun for one day, or until wilted.

The recorded method does not give a numerical temperature, relative humidity or target weight loss.

Wilting makes the vegetables more flexible and helps them fit compactly into the jar.

4. Pack the vegetables.

Arrange the wilted greens in a clean earthenware jar.

Compact them sufficiently to make room for the liquid.

Avoid leaving large unfilled cavities.

5. Prepare the salt-and-sugar liquid.

Dissolve 1 cup salt and 1 cup palm sugar in 2 cups water.

Stir until the ingredients are distributed.

The recorded method does not specify a heating temperature or a required boiling stage.

6. Add the rice-associated liquid.

Prepare 3 cups rice-wash water.

The traditional record alternatively permits cooked rice mixed with water, but does not specify the rice quantity for this option.

Combine the rice liquid with the prepared brine.

7. Cover the vegetables.

Pour the liquid into the jar so that it covers the packed mustard greens.

Release large trapped air pockets and keep the vegetable material below the surface.

The goal is a consistent fermentation environment rather than floating leaves exposed to the air.

8. Close the jar.

Cover the vessel using an appropriate fermentation arrangement.

Do not use an unsafe rigid seal that can build pressure without relief.

The historical source specifies closure but does not provide modern pressure-management instructions.

9. Ferment.

The documented method exposes the jar to sunlight for 3–5 days.

Because neither the internal product temperature nor the final acidity is provided, this is a traditional method description rather than a validated safe procedure for uncontrolled sun exposure.

10. Assess and store.

The expected result is sour, mildly salty and slightly sweet.

Use appropriate acidity and microbial controls before treating a batch as successfully preserved.

The historical storage claim of 1–2 months is not a guarantee of safety under arbitrary modern storage conditions.

How the fermentation works

The principal desired process is lactic-acid fermentation.

Plant-associated lactic acid bacteria can use sugars available in the vegetable and liquid.

The organisms produce lactic acid, lowering the pH and developing the distinctive sourness.

The JIRCAS database identifies organisms including Lactobacillus brevis, Lactobacillus plantarum and Pediococcus cerevisiae, together with yeast groups.

These are historical scientific names.

Some modern classifications have changed, and the exact species composition of an individual batch cannot be inferred merely from the product name.

Acid production depends on the balance between microbial growth and the available carbohydrates.

The palm sugar adds a substantial quantity of soluble sugar.

Rice-derived material supplies additional substrates or suspended carbohydrates.

The vegetables contribute their own soluble nutrients.

Salt selects for organisms able to function in the brine.

The result is a microbial environment substantially different from pure unsalted vegetable spoilage.

Nevertheless, the process is not automatically safe at every possible temperature.

Why sunlight matters — and why it is difficult to reproduce

The historical process places the vessel in sunlight.

Sun exposure can warm the jar and influence fermentation rate.

In a traditional household setting, the maker may have understood the local climate, season and position of the vessel.

But a glass or earthenware container exposed to intense sun can become considerably warmer than the surrounding air.

The exact temperature depends on vessel material, color, volume, wind, cloud cover and sunlight intensity.

The recorded method does not provide an internal temperature profile.

For this reason, its instruction cannot be translated into a claim that the food should be held at any particular numerical temperature.

For a controlled modern process, temperature measurement and an established safe range would be necessary.

The general extension ranges for vegetable fermentation do not validate direct sunlight as a suitable temperature-control strategy.

Changes in texture and color

The finished greens are described as yellowish-green.

Several processes contribute.

Wilting reduces turgor.

Salt changes cellular water distribution.

Acidification alters the chemistry of the vegetable tissues and their pigments.

Chlorophyll is sensitive to acidic conditions, and the color can shift away from fresh green.

The stalks may remain somewhat crisp while the leaves become softer.

The precise texture depends on mustard variety, size and fermentation conditions.

The desired result is not identical to raw mustard greens and not necessarily as soft as thoroughly boiled vegetables.

Color and softness are sensory descriptors, not safety measurements.

Difference from the high-salt method

The two JIRCAS methods should be compared carefully.

Main salt addition — 8–10% by vegetable weight — 1 cup per 2 kg vegetables

Added carbohydrate — 2% cooked rice — 1 cup palm sugar plus rice-wash liquid

Free liquid — Primarily released by vegetables — Added brine covers the greens

Fermentation — 5–10 days — 3–5 days

Flavor — Predominantly salty — Sour, salty and slightly sweet

Historical storage claim — One year — 1–2 months

Those differences are sufficient to treat them as distinct recipe variants.

The storage figures describe traditional observations. They do not establish which method is safer under modern conditions.

How the finished product is eaten

Pak-kaat-dorng is eaten as a preserved vegetable side dish and as an ingredient.

One traditional Thai use is a light soup with pork ribs.

The preserved greens are boiled with the meat and served with rice.

The vegetable supplies sourness and saltiness, while the pork enriches the broth.

Other contemporary Thai dishes use chopped preserved mustard greens in noodle preparations or as a condiment beside rich braised pork.

The sourness is particularly useful with fatty foods.

Commercial pickled mustard greens may taste sweeter, saltier or more acidic than homemade versions.

It is therefore sensible to taste a safely produced product before adding additional salt or acid to a cooked dish.

Recognizing a satisfactory result

The documented finished product is sour, yellowish-green, slightly sweet and salty.

The sourness should reflect proper acid development rather than putrefaction.

Unexpected mold, decayed odors, contaminated brine or abnormal deterioration indicates failure.

Floating leaves exposed to air may be vulnerable to surface spoilage.

Bubbles can accompany fermentation but cannot prove sufficient acidification.

The recorded method does not give a final pH, finished sugar concentration, salt concentration by mass or measured water activity.

Safety and storage

The recipe involves spontaneous fermentation under an imprecisely specified temperature regime.

It should not be presented as a validated shelf-stable preservation method.

General produce-fermentation guidance identifies pH 4.60 or lower as an important safety threshold, but that does not establish that this historical Thai method reaches it consistently.

A cup measure of salt also creates uncertainty unless the salt type and mass are controlled.

For commercial or experimental production, finished acidity, salt concentration, microbial quality and storage conditions must be validated.

JIRCAS reports a traditional keeping period of 1–2 months, but the database does not establish a tested modern refrigeration or ambient-storage regime for that duration.