Each province in Isaan prepare somtum differently
Each province in the northeast has its own distinctive way of fermenting plara, hence the people in Isaan tend to eat somtum in different ways. Those in the lower Isaan region, like Khon Kaen, usually consume papaya salad with pla ra kaeng, which means they like their somtum with milder and more balanced flavors. On the other hand, folks in upper Isaan, like Nakhon Phanom or Ubon Ratchathani, tend to enjoy their somtum with stronger flavors, and end up with making their salad with pitch-black fish juice which most people find unbearable. Pla ra is usually salty but the version in Nakhon Ratchasima has a sour taste because its residents substitute rice bran for toasted rice, which results in more acidity during fermentation. Also, while somtum sua in Bangkok and in most provinces refers to somtum mixed with khanom jeen (fermented rice noodles), it means a different thing in Nakhon Phanom. Their variation entails raw papaya, khanom jeen, pickled cabbage and num ya pla pon (grounded fish curry). In other words, it’s like you’re eating somtum and khanom jeen curry at once.
There is a similarity between pad Thai and somtum Thai
Both are appropriations of regional cuisine by—and probably for—Bangkokians whose palates are, supposedly, more refined. The idea of eating juice made from raw fermented fish may sound repulsive to some, so it was replaced by (num pla) fish sauce in Bangkok. Num tarn peep (palm sugar) was injected to add the sweetness that central Thais usually crave. Pad Thai, which evolved from Chinese noodles, was appropriated in pretty much the same way. Both dishes share the same ingredients: salted dried shrimp, roasted peanuts and a sprinkling of sugar.
Somtum was traditionally a main dish but centralization made it a starter or a side
Papaya salad was considered a staple for Isaan people, and it was simply eaten with sticky rice and grilled chicken. When somtum arrived in Bangkok, where the sumrub food culture—a single meal composed of a variety of dishes that combine different textures and flavors—greatly influence how people eat, the Isaan dish soon became a side dish along with many other northeastern delicacies like larb and spicy soup. Even now in Isaan, you would rarely see people eat only somtum with sticky rice.
It’s impossible to standardize somtum
Somtum is considered a very personal dish in Isaan—each family has its own preference and recipe. So you cannot really pinpoint the proper way to make the delicacy. Most papaya salads served in somtum shops, even in the northeast, are made to please diners, and it’s quite normal for eateries in small villages to allow customers to prepare the dish themselves. And because of the many variations surrounding the dish, somtum cannot be reduced to a single recipe. The definition of somtum has broadened over the years and is still open to interpretation. Technically, somtum doesn’t have to be made from raw papaya; it can be made with any sour or unripe fruits or vegetables, such as unripe bananas, mayom (super sour berry) and kraton (santol). So, just like Phed Phed which has somtum taling pling and somtum strawberry, anyone can come up with their own recipe for somtum.