As mentioned above, canh chua can be a pretty variable dish. This is great, as it allows you, the reader, to try out plenty of different ingredient combinations. It can, however, be a little overwhelming. But fear not! In this section, we're going to break down the recipe (and its variations) by looking at three specific categories: the base, the herbs, and the focal ingredient(s).

If you want to jump right on into the recipe, you'll find that it's pretty easy to follow, so if you're looking to make the soup that you see in these photos, feel free.  That being said, understanding your options will help you to modify the soup to your own personal tastes.

Finally, it's worth noting that canh chua, like many other Vietnamese dishes, can be pretty extensively tweaked to individual tastes at the table.  An array of condiments allow individual diners to modify many aspects of the dish, so don't feel like you need to end up at one perfect end-point right out of the pot.

As with so many soups, the quality of your soup stock is going to play a huge role in how well your canh chua turns out. That being said, you have a lot of options over what that stock can be. Chicken, fish, and vegetable stocks all make excellent starting points. I suppose you could try a beef stock too, but that's going to lead to a much bigger shift in the overall flavour of the soup, and it's a lot less likely to play well with seafood and other light meats.

Once you've decided on a base, you'll want to think about how you're going to sour your soup.  Tamarind paste is the overwhelmingly popular choice for canh chua. Tamarind paste can be found at a wide variety of grocery stores, especially those catering to South and Southeast Asian communities.  Note that tamarind paste can be fibrous, so you may want soften and strain it with hot water or stock ahead of time.  My friend Pailin from Hot Thai Kitchen demonstrates this method very nicely here.  You can also add the pulp into a little strainer, then dip this into the broth and press the liquid through into the stock.

If you can't get tamarind paste, there are other souring ingredients out there, and indeed other types of canh chua!  Within Vietnam you'll find some canh chua recipes in the north that use sour fermented bamboo, for example. Of course, most readers are probably not going to be in a situation where sour bamboo is plentiful while tamarind is not.

So, can you substitute for tamarind paste? Yes... to an extent.  A mixture of worcestershire sauce (which contains tamarind), lime juice, and brown or palm sugar makes a pretty reasonable substitute.  Recipes vary, but I recommend starting with about 2 teaspoons of Worcestershire sauce and two tablespoons each of lime juice and sugar.  Bear in mind that some of these ingredients can also used as condiments at the table, so don't feel that you need to get the ratio bang-on right away.  All this being said, remember that tamarind is much more than a souring agent - it provides a unique and distinctive fruity flavour that's not easily replicated.  Canh chua without tamarind can still be good, but don't expect a one-to-one substitution.

Finally, it's worth noting that the pineapple and (to a lesser extent) tomatoes will further add to the sour flavour of the finished soup - so you don't need to expect the soup base itself to do all the heavy lifting.

You've decided to make canh chua... but what KIND?

The version shown here is a mixed soup, with firm white fish and whole prawns.  I like this version because it's got the best of two seafood worlds, and because it's simple and accessible.  You can easily do just fish, just prawns, or... well, plenty of other things. Here are a few options to get you started.

1. Fish - The sky (or the sea?) is the limit on this one, as a wide variety of fish species can be used here.  White fish like basa (which I used), catfish, and snakehead are all popular.  Cod, halibut, sole, rockfish, snapper, and any number of other fish species popular in North America and Europe would work very nicely too.  More robustly flavoured fish like salmon and eel are also popular, though they will of course contribute a more prominent flavour to the finished soup.
2. Shellfish - Shrimp are classic, and there are plenty of different kinds of shrimp out there to experiment with.  Other crustaceans like crab and lobster are lovely, if you've got them.  Squid is excellent.  Clams and mussels are excellent choices, but you'll need to use more of them to account for the weight of the shells (clams in particular have rather heavy shells).  The flavours of these different ingredients are by no means interchangeable, but they're all great in canh chua, and they give you plenty of options for shaking up the meal.
3. Chicken - Easy to get, easy to use, and wonderfully neutral, chicken makes for a great, simple protein choice.  I personally think chicken works best with extra herbs to add some punch to the more neutral meat.
4. Pork - Particularly popular in many northern variations, pork (generally either minced or as short ribs) works very nicely, particularly alongside fermented vegetables (see below).
5. Vegetables & Herbs - These are going into any canh chua regardless, so why not make them the focal point?  Boldly flavoured ingredients like pickled mustard greens and bamboo shoots are a great choices, and also compliment many of the meats very nicely.  Hearty leafy greens like water spinach (rau muống in Vietnamese, commonly sold as Ong Choy in North America) make excellent and very healthy choices.
6. Tofu - Simple and filling, tofu (much like chicken) is an easy choice, albeit a somewhat neutral one.  Consider pairing tofu with other more boldly flavoured ingredients.  Softer tofu varieties will soak up the soup better.  Previously frozen tofu holds up better as it cooks, and tends to soak up flavours even better still.

For meat and seafood variations, I aim for 500-600 grams (1.1-1.3 lbs) of meat, and perhaps less for pork.  Be sure to take into account the weight of any non-meat portions (e.g. shells and bones) before you start cooking.  If you want to use even less meat, consider adding some tofu, or just more hearty vegetables.

For vegetable and tofu variations, quantities are a little harder to nail down.  If you're using a soft or medium-firm tofu, I would use about 450 g (1 lb).  For firm tofu, I would use less, as it's quite dense and filling.  Vegetables and herbs are, of course, going into all the variations, so if you're focusing on a veggie-centric canh chua I would recommend focusing on how big of a flavour impact the ingredient will have.  A highly flavourful herb or green vegetable might be better in smaller quantities, while taro stems are airier and more neutral.  If you're adding more okra, be aware of the thickening effect that this vegetable can have! If you love okra and you want to use a lot of it, consider baking or searing it ahead of time.

Finally, a note on balancing your flavours around different core ingredients: don't be afraid to adjust the soup base to taste based on the impact of the ingredients you add.  You might find, for example, that you want more or less cumin for some variations, or more shallots.  Trust your taste buds, and experiment.

One of my favourite things about Vietnamese cooking is the approach to fresh herbs. They're used liberally and boldly, bringing big, bright flavours to all kinds of dishes. Unfortunately, some of the most popular and distinctive Vietnamese herbs can be tricky to find outside of Southeast Asia. In this section, we'll look at a few key herbs, where you might find them, and what you can do to substitute for them.

Note that any (or all!) of these are great with canh chua.  Don't stress out too much if you can't get one in particular, but if the opportunity arises to try an herb you don't get to use all that often, I highly suggest going for it.

1. Húng quế (Thai basil) - Ocimum basilicum var. thyrsiflora
   A cultivar of sweet basil with more pronounced flavours of anise or licorice.  Thai basil is generally easy to find at well-stocked Asian grocery stores.  The distinctive anise-like flavour of Thai basil makes it difficult to substitute for, but there are some varieties of sweet basil that do have more prominent anise notes.  However, these are generally going to be even less common in stores that Thai basil itself.  If you absolutely can't get Thai basil but you want some basil flavour, try adding a couple of blades of star anise to the soup base, then garnish with some minced sweet basil.
2. Rau răm - Persicaria odorata
   Sometimes called Vietnamese coriander (which is a confusing name, as it's not related to coriander at all), this herb is actually a relative of buckwheat.  The flavour is bold - some consider it to be similar to cilantro (coriander), while others don't.  Regardless, it has a a more pronounced pungent/spicy character, with a somewhat citrus-like element.  It can be slightly bitter too.  Substituting for rau răm is tricky, as it isn't quite like any one other ingredient.  I suggest balancing your soup out with a bit more citrus, chili, and other herbs instead.
3. Ngò gai - Eryngium foetidum
   Also called long coriander or culantro (once again, not to be confused with true coriander/cilantro).  Like true cilantro/coriander, ngò gai is a part of the carrot family (Apiaceae).  It tastes rather similar to cilantro, albeit somewhat stronger.  Whether or not you find this herb easy to locate is probably going to depend on your local culinary communities; in addition to being used in Southeast Asian cooking, ngò gai is also popular in Caribbean and South American cooking.  Grocery stores catering to any of these communities are going to be your best bets when it comes to finding this herb.  When it comes to substitutions, you're generally going to have the easiest time finding and using true cilantro/coriander.  If you don't LIKE cilantro... well, you probably won't love ngò gai.
4. Rau mùi/rau ngò (Cilantro/coriander) - Coriandrum sativum
   Used extensively in Vietnamese cooking, cilantro (if you're in North America) or coriander (if you're not) is pretty widely available and easy to find.  It makes a great substitute for harder to find herbs like rau răm and ngò gai, though it tends to be a little milder than those.  Cilantro/coriander can be found pretty easily at most grocery stores these days.  It's also easy to grow.
5. Ngò ôm/om (Rice paddy herb) - Limnophila aromatica
   A classic ingredient in canh chua, this this water-loving herb has a flavour somewhat reminiscent of lemon and cumin.  It's great, but hard to find outside of grocery stores catering to Southeast Asian communities.  I use cumin in my canh chua broth to make up for the fact that I can't readily obtain ngò ôm.  You can vary the quantity to your tastes.
6. Hành lá (Scallions) - Various Allium species
   Scallions (green onions) are more commonly found in Vietnamese cooking outside of Vietnam because of their ready availability, but they make a lovely addition to canh chua and other dishes.  Scallions are especially nice to have on hand for any cilantro-averse diners you might be feeding.  Generally only the green parts of the stalk are going to be used in this situation.
7. Hẹ (Chinese/Garlic chives) - Allium tuberosum
   These long, thin onion stalks are similar to scallions in many ways, but with a much more pronounced garlic flavour.  The leaves tend to be flat, rather than hollow.  Garlic chives are easily found at most Asian grocery stores.  They make a particularly nice addition to canh chua (and other Vietnamese dishes) for diners who can't get enough of that pungent garlic taste.

As I mentioned above, herbs add a fantastic potential for customization to all sorts of Vietnamese dishes - but they're not the only add-ins on the table. A wide variety of condiments can be used to modify servings of canh chua to individual diners tastes.  You certainly don't need to have all of these on the table all of the time, but it's wonderful to be aware of the roll they can play.

1. Fish sauce - Adds salty, umami-rich flavour.  I highly recommend shopping around to find a brand of fish sauce that you particularly like - but that's really a topic for another day.  Remember that a little goes a long way.
   
   
2. Fried garlic - Adds texture and a punch of caramelized garlic flavour.  Personally, I consider this ingredient a must-have for canh chua, as I think it perfectly accentuates the sweet/sour nature of the soup base.  You can buy fried garlic chips and pieces at a wide variety of grocery stores (including, unsurprisingly, Vietnamese shops), but if you have the time, I highly recommend making your own.  It's quick and easy, and you get the added bonus of getting a batch of garlic oil out of the process.  Hungry Huy and Serious Eats both have good how-to guides.
   
   
3. Citrus - Adds acidity/sourness. Limes are probably the best option here, but lemon can work nicely too.  Canh chua is generally going to be sour enough as-is, but citrus the extra little punch of lime can be quite nice nonetheless.
   
   
4. Sugar - Adds sweetness.  Pretty self-explanatory. Sugar can help to round out canh chua, and helps to make up for the natural variations in sweetness found in pineapples and tomatoes.  I recommend using grated or crushed palm sugar, but a light brown sugar works too.
   
   
5. Chilies - Adds spice/heat.  Totally optional, but nice to have for those who like their soup on the fiery side.
   
   
6. Herbs - See the section above.