Sourness is one of the tastes that contributes to the well-rounded characteristics of Thai cuisine, a palatable subtlety that comprises sour, sweet, nutty, salty, spicy, bitter, tart and mild tastes.
The sour taste, like other flavours, is enjoyed as an expected feature of natural ingredients rather than through seasonings or condiments.
In a samrab (a traditional Thai meal consisting of various dishes to be eaten with rice), sour taste is commonly found in a nam phrik (relish) dish.
A choice of tangy native fruits such as ra-kam (salacca), ma-uek (hairy eggplant), kra-thon (santol) and talingpling (bilimbi) may be pounded into the mixture of nam phrik, while other recipes may be served with sour-tasting fresh young leaves of ma-kok (Thai olive) and makham (tamarind) as a part of the accompanying vegetables.
Despite Thailand's various choices of tangy ingredients, over recent decades, especially in urban food areas, manao (lime) seems to be the predominant provider of the people's sour pleasure.
The demand for manao, which can fetch a high a price of 15 baht each in summer, is so massive that the fruit overshadows other sour-tasting counterparts that are also treasured throughout the country.
Som khaek contributes to the sour taste in many southern Thai dishes.
As a matter of fact, according to food culturist Krit Luea-lamai, manao should not be considered the holy grail of sour taste in Thai cuisine.
"People experience tastes differently. Sourness for some people may be just a delicate hint of acidity, while for others it can be much more complex and intense," he said.
Thus, in his view, lime has the same significance in Thai cuisine as tens of other sour-tasting native ingredients.
"In esteemed age-old Thai cookbooks, you will find recipes that depend on the sour taste from tamarind paste, ma-dun (garcinia), som-sa (bitter orange) or ma-krood (kaffir lime), or juice of pickled garlic, but not lime. Lime may be used as a borderline addition should the dish not be sour enough."
The availability of ingredients nearby also contributes to local recognition of taste, explained Krit. And when it comes to an appetite for sourness, folks upcountry benefit from their horticultural diversity.
Tamarind, a quintessential ingredient.
Ma-sang (feroniella), som men (young tangerine), som khaek (asam keping fruit), makham moo (green tamarind), ma-peed (miniature orange) and lemongrass berries, according to him, are among the zesty fruits commonly found in regional cuisines as are the tangy young leaves of mango, tamarind, olive, cha-muang (garcenia cowa) and phak tiew (mempat tree).
The petals and pollen of some plants including roselle, red ginger lily, mempat tree and rose apple are also used to add tanginess to dishes.
Sources of sourness in provincial cookery are not limited to botanicals. Animals, too, can provide a tangy sensation.
Mod daeng (red ants) and malaeng da na (giant water bugs) are popular edible insects cherished for their unique fragrance and sour taste.
Yum khai mod daeng (spicy salad of red ant roe, a popular dish in northern Thailand) features a delicious unification of creamy roe and sourness from the ants.
Rural folks are very creative in working with nature, according to Krit.
Giant water bugs are cherished for their distinctive scent and sour taste.
"In Isan, some people put marinated chicken in a red ant nest before grilling. By allowing the ants to chew on the chicken, the chicken meat is imbued with astringency from the formic acid in ant saliva. The ants that are left on the chicken when cooked, unintentionally or on purpose, will add another layer of sourness to the delicacy."
Unfortunately, rustic culinary techniques and indigenous produce are just some of the long-preserved culinary wisdom that seems to be undervalued in present-day gastronomy.
Supanat "Ann" Khanarak, a veteran chef and instructor, observed that some native citrus which were once prevalent in classic recipes have now become bygone culinary jargon.
She said som-sa (bitter orange) is an obvious example.
"Som-sa is for me one of the most amazing ingredients in Thai cuisine. Its sourness may not be as sharp as that of a lime, but it has a unique aroma and depth of flavours that can nicely enhance many Thai dishes, both savoury and sweet," chef Ann explained.
"But today, som-sa are quite hard to find and those available in a Bangkok market may cost as ridiculously high as 100 baht per fruit."
Red ants are a common ingredient in northern and Isan cuisines.
The chef sadly recalled that during her cooking classes, some of her students used just a third of the fruit and threw the rest away.
According to her, the juice and zest of the rough-skinned, lime-sized citrus are ideal components in mee krob (sweet and crispy noodles), khanom jeen nam phrik (fermented rice noodles with peanut curry), massaman curry and som chun (a dessert featuring seasonal fruit in chilled syrup).
Although passionate about som-sa, chef Ann -- an avid fan of tangy food -- admits that her kitchen also enjoys the ever-presence of lime.
"I like using manao because it instantly gives a bright dimension to the dish."
But it is not just any kind of lime, especially not the seedless hybrid cultivar, she noted. Her preferred variety is manao pan, a fine-skinned lime with a sweet delightful fragrance and plenty of sharp-tasting juice.
"Most people of the younger generation don't realise the multifold character of ingredients," chef Ann said.
"They appreciate sour food just for the acidic zest on the palate, forgetting that the sour, bitter or tart flavour of the ingredient also indicates its medicinal value."
She mentioned poramat, a bite-sized snack offered to Buddhist monks after the noon meal during which time food should be absent.
A poramat, according to chef Ann, consists of herbs such as galangal, ginger and chillies together with sour-tasting fruits such as sa-mor (baheda fruit), makham pom (Indian gooseberry) and lime, all wrapped in a betel leaf. Though looking like a pastime nibble, poramat is regarded as a medicament for the monks because of the curative properties of the ingredients.
"To better appreciate the universe of sour taste, it's a good idea to begin by exposing your palate to wider choices," Krit said.
"The availability of provincial ingredients in Bangkok today is voluminous compared to 30 years ago, when finding them in the city was almost impossible. The abundance of supply follows demand by labourers from upcountry. You just need to know where to look for them," he added.
According to him, major fresh markets in the city's suburbs including Talad Bang Bon and Talad Phran Nok carry several ingredients mentioned in this article.
