Something that you are going to see almost everywhere when you are visiting here is something called "Som Tum" or on menus that are in English it might just say something like spicy papaya salad. This is a truly delightful dish that is extremely cheap almost anywhere in the country. It originates from the North East area called Isaan and it's so well-liked that it is available in every city regardless of size. It is very easy to find this on almost every street corner for a dollar or two and it is something that shouldn't be missed. You should know the ropes going in though because this can be extremely spicy to the point of being inedible for most foreigners, including me.
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There are many different varieties of this local favorite but for simplicities' sake and because I only really know about the most popular one, I am going to focus on "Som Tum Thai" which will always be available because it is the most basic version. The mixture consists of fresh cut papaya, peanuts, lime, fish sauce, dried shrimp, chilis, and some other herbs that I am not going to pretend to know what they are. There will be some variation but for the most part this is all there really is to it.
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The cook will take all of these things and then bash them with a mortar and pestle in a somewhat aggressive way. Some people will jokingly refer to the dish as "papaya pok pok" based on the sound that it makes when they are making it.
The most important part of the process is indicating how many chilis you want in your mix. A lot of people come over here thinking that they can eat spicy only to find out the hard way that the Thai notion of what "spicy" means is considerably different than most other countries. To some Thai people, they have been eating spicy food their entire lives daily and therefore they will need a lot of chilis in order for it to achieve that level of burn that they want. This notion of "spicy" in the heads of most Thai adults is akin to something that is going to give me hiccups immediately, have my mouth be on fire for half an hour and is food that I cannot possibly consume.
So the trick here is to just take it easy on your first couple of orders because while you can always put more spice in, you can't take it out at all. For me my max spice level after years of living here and having this dish every week at least once is 5 of them. If I want a more relaxing meal that isn't going to potentially hurt me, I play it safe and go with 3.
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Thai chilis might not look like much but man oh man do they pack a punch. If you don't believe me take a bite off the tip of one some day as they are usually on every table in every restaurant. To put things into perspective Tabasco sauce has a Scoville (rating used for spiciness of anything) rating of between 2500 and 3000. A Thai chili is anywhere from 50,000 to 100,000 on the same scale... so yeah, it's pretty spicy.
To play it safe maybe order your first Som Tum with only one chili and see what that does for you. It costs almost nothing and is still delicious even without chilis in it so it's not like you will be wasting money.
If you do decide to get a bit daring with the spice make sure to spend 10 Baht on some sticky rice on the side because water is useless against the spice whereas putting some sticky rice in your mouth to absorb the spice kind of works. Mostly if you overdo it on the spice you are kind of stuck with what you ordered so play it safe.
This cheap and widely available dish is something that people visiting this country shouldn't miss, but if you do it wrong it will punish you!