On several occasions I described Thai soups. The awesome variety of ingredients, preparation methods and spicing, makes it almost impossible to make a complete review of them. At certain point one realizes the task is impossible, each soup stall has its own peculiarities and flavors. Yet, the spices box offered by this respected establishments display a Pythagorean exactitude that would make NASA engineers envious. No chance of confusing miles and kilometers here, the basic set invariably displays four spicing options. Before commenting on them, I must say that sometimes other options are available: limes and mint leaves are common additions, as well as Sriracha sauce, nam prik chili sauce, sweet chili sauce and even more exotic spices. Yet, the obligatory spices are just four. Luckily, there is no chance of mixing them up.
Nam Som Prik, literally "water sliced chilies," is a watery sauce of sliced green chilies in vinegar. It allows making the soup hot and sour.
Nam Phla—"water-fish"—is a fermented fish sauce. The sauce is prepared by rubbing fresh fish with salt and putting them into a jar topped with bamboo bracts. Then they are left for two months, the juice coming out is filtered and used sauce; its smell leaves no doubt with regard of its content. It may be enriched with chopped raw chilies, lime juice, and sometimes also garlic. This sauce allows making the soup hot and salty; note that pure salt is not offered in Thai eateries.
Prik Pon, the third spice, is pretty clear in nature: ground roasted chilies. With a deep earth color, this spice is invariably very hot, but its spiciness degrees vary. The hottest Thai chili is a small variety known in the West as "bird's eye chili," but called in Thai phrik kee noo, literally mouse dropping chili. The odd name obviously refers to its small size, but it also has another connotation in Thai. Mouse—"noo"—is a popular nickname used while addressing young children. "Kee" in its own means "dropping," but it is often used to describe negative by-products of one’s personality, like for "lazy"-"kee gee-at." Here, it is used in the same way the English word "bad" may be used in slang to denote a positive thing. This one is used to make the soup just hot. Phrik kee noo is wildly hot—and thus an excellent chili in the Thai world—thus it earned the negative qualifier "dropping." If used as a spice while frying something within a wok—as street vendors often do—its vapors are said to be capable of blinding even many miles away from its ground zero.
Nam Tan, is the fourth condiment. Its white grains should be immediately recognizable; yet, its odd location in a soup stall causes hesitation in its recognition by Westerners. It is just plain white sugar.
The exactitude in which this spices are placed is not casual. All of the four spices are mathematically added to each bowl of soup. Yet, this is one of those occasions were studying the local custom and then following it is not recommended. Thais from Bangkok would add a teaspoon of each of the first three spices and then top that up with a large spoon of sugar. Doing that during the first time one experiences the dish, may ensure it would also be the last time. A graphic description that may ease to understand this is that rice-noodles—strikingly white in nature—often come out pink out of the concoction after being washed in mouse dropping chilies.