In Thai, som dtum means "to pound something sour" and is, alongside padt Thai, one of the standard-bearers of the cuisine. It's served everywhere - at markets, festivals, restaurants and by the roadside - and of course every good home cook claims to have the best recipe.
Som dtum is so highly regarded in Thailand that it even has a song dedicated to it, a pop hit written by a Thai princess and immortalised by the late Poompuang Duangjan, Thailand's answer to Madonna. It was number one on the charts in Thailand for weeks and is taught to kids as a song of great national pride to this day. And its lyric content? A step-by-step guide on how to prepare green papaya salad, pure and simple.
Happily, the basics are straightforward and once you've mastered the core recipe, there's no shortage of variations to keep things interesting. It could be as simple as adding lime rind for another layer of depth, or as exciting as mixing in some pickled crab. You can beef it up by adding other vegetables - apple eggplant is a popular addition. Each region of Thailand has its own take and, of course, each claims superiority.
In central Thailand, the most common version is som dtum Thai, which is as basic as it gets while using the key ingredients. As you get further away from the centre of the country, the funkier and spicier it becomes. Around rice-growing regions, for instance, it's common to send the younger kids out on a mission to catch the small freshwater rice-paddy crabs. They're pickled whole or chopped up and brined, and the result, known as bpu dorng, is added to the salad.
Another common water creature that finds its way into som dtum is the snakehead fish. Fermented raw with salt, water and rice bran in large clay jars, it becomes pla ra, and the salad made with this pungent condiment, popular in the Isaan region of Thailand's north-east is called som dtum pla ra.
While these strongly flavoured variations can be challenging to the uninitiated, their mere scent can almost overwhelm a member of the Thai diaspora with nostalgia. And, practically speaking, both bpu dorng and pla ra add a rich umami depth to everything from chilli relishes to curries; the key is to add them with a deft and courageous hand.
At Chat Thai, our som dtum Lao is a particular hit with Thai diners. It combines both the pla ra and bpu dorng among other ingredients. It's not one for the fainthearted, but it has a deliciousness all its own. We also serve this as som dtum taart - the salad augmented with fermented rice noodles, pork sausage, soft-boiled eggs, fresh herbs and cracklings. These accompaniments both tame the heat and make the dish a meal of more substance.
Though you can at a pinch prepare som dtum without any special equipment, there are two pieces of kitchen kit that make all the difference. Neither is particularly expensive and both should be readily available at your local Asian grocer.
The first and perhaps most essential of these is the papaya shredder, a wavy-bladed implement that looks a bit like a vegetable peeler. The Kiwi brand is the one we use at our restaurants, and you should be able to pick one up for about $10. The second is a Thai-style mortar and pestle. Our mortar is a baked red clay number with deep sides, and the pestle is long and made of wood.
A long-handled metal serving spoon is also very helpful for mixing your ingredients around in the mortar.
The flavours, ingredients and technique
To my mind, the difference between a great som dtum and one that's merely good comes down to that balance of flavours essential to so much of Thai cooking. Can you taste the sour, the salt and the sweet? Is one overpowering the other? How much heat do you want? How much can you handle? Simply setting your mouth on fire doesn't make it a fantastic som dtum by any means. The heat should sneak up on you after the flavours play around in your mouth. A truly great som dtum will have you using grilled meats and sticky rice to soak up every drop of the dressing at the bottom of the bowl.
Starting with the right papaya is, naturally enough, very important. It should be so crunchy that chewing it all but blocks out every other sound in the room. The variety I like is called kaak dum. It's long, and when it's at the right stage of unripeness for som dtum it's dark green. The size doesn't matter so much; choose one that you can use up in one meal. The peeled flesh should be very firm, a lovely pale-green colour, and ever so slightly sweet.
Peel the papaya, cut it in half horizontally and remove any seeds, then start shredding. The strands should be long and even. Rinse them under cold water for five to 10 minutes to get rid of any sap, then immerse them briefly in a bowl of iced water, which keeps their texture crunchy. Drain them, then put them in the fridge so they stay cool and crisp until you're ready to dress them.
The order of the recipe is also vital - the raw garlic, which lends both punch and spice, needs to be finely pounded, as does the chilli, before the liquid ingredients are added. Two birdseye chillies provide enough heat for most diners, but by all means add more; seasoned customers at the restaurant ask for as many as five or six. Approach that number with caution.
The palm sugar we use is called Baan Darn Buk, and it's quite malleable compared with other brands. It goes in at the same time as the garlic and chillies because you want the paste ingredients mixed well before you proceed. Once you've got that sorted, in go the dried prawns (they're small, so they're often labelled shrimps). When you're buying them look for shrimps that are plump, with a vibrant orange colour. We use the small peanuts popular in Thailand, and it's important to dry-roast them yourself fresh to order for the best flavour and mouthfeel.
The nuts, like the prawns and the beans, should be crushed, but you don't want them reduced to smithereens. That goes double for the cherry tomatoes; these should just be pressed enough to release their juice and seeds into the mix to add their sweetness and acidity. We use the commonly sold Squid brand of fish sauce for its salty strength, and I hope it should go without saying that the lime juice has to be squeezed fresh.
Add the fish sauce and lime juice and mix well with the spoon; then, and only then, should you add your shredded papaya straight from the fridge. Don't go crazy with the pestle at this stage - from here it's more of a toss-toss-toss-pound routine. Repeat that a couple of times, but once all your ingredients are coated with the dressing, stop.
Freshness is best here. We pound our som dtums to order, and when you're making it at home it's best if it's the last thing you do in the kitchen and the first thing you put on the table, otherwise you'll end up with a soggy salad.
Som dtum likes friends at the table. It goes really well with grilled meats such as chicken or pork shoulder, and its classic accompaniment, sticky rice, comes in handy to mop up the juices. Let's get pounding.
This recipe makes a large serving for one - a mortar and pestle generally takes only this amount, though you could double it, but no more than that. It's the sort of dish that works best shared as an accompaniment and this recipe makes a side for two to three people.