Most provinces I have gone to have their own version of sinigang. Maybe because cooking sinigang is easy and that it is a complete meal in itself (meat, carbohydrate source, vegetables, soup...). I am not sure why we have grown accustomed to having sinigang as sour (as most Pinoy rice partner dishes are salty and spicy). Personally I prefer enjoying my sinigang piping hot and the more sour the soup, the better. I could not imagine sinigang without any pampaasim, till I tasted the Bohol version (which tasted more like nilaga). With no offense to my Boholano friends, I still would want to squint my eyes while eating a sinigang meal. Pampaasim spices should always be available in most Pinoy households, not only for sinigang but also for kilawin and paksiw dishes. Most of the time, these plants are being grown as backyard ornamentals.
The most easily available pampaasim is sampalok or the fruit of Tamarindus indicus. The tamarind grows big and has fine pinnate leaves typical of leguminous trees. It has become a favorite tree and could be seen almost in all corners of habitation including bustling Metro Manila. Sampalok is however not native to the Philippines. It got introduced early on with the influx of prehistoric migrants coming from mainland Asia. As its name suggests, T. Indicus originates from India and its neighboring countries. This very popular pampaasim is the first choice for sinigang, but personally I prefer it to be cooked with pork or chicken (sinampalukan, using leaves rather than the fruit) as main ingredient.
Another readily available pampaasim is the common and very useful calamansi/kalamondin or Citrofortunella microcarpa. The calamansi is actually an old cultivar of native Citrus plants (relatives of the orange and limes). It has been used extensively in Filipino and other Asian cultures that its exact origin has been obscured. But its domestic importance has been passed down from one generation to another. In cooking, the calamansi is preferred to be used for seafood dishes, to remove the foul fish or seafood taste. Calamansi is therefore best in cooking seafood sinigang.
A different experience is when beef sinigang is cooked using guava or bayabas as pampaasim. Personally I do not enjoy beef dishes but what I remember from my mom’s beef/ guava sinigang is that it has the most identifiable taste. It is very undeniable when the fruit is used because of the somewhat sweet fruity flavor. Guava or Psidium guajava is an import from tropical America and probably one of the recent choices for sinigang sub acid component, maybe why it is less popularly used in the dish.
I was once told that the souring agent choice for cooking fish sinigang is Averhhoa balimbi or kamias. The easily grown plant is also very much available in Tagalog communities. So bountiful that it is almost certain that kamias fruits are always available for cooking, and if not the plentiful harvest could be dried up or pickled, to be stored for future use. The kamias is probably the most sour-tasting among the mentioned, minus an identifiable fruit flavour that the other candidates have. It is long been domesticated like the calamansi. I tried to confirm where this plant originated but got confused by the contradicting facts. But it is certain that it is not a native of the Philippines.
The native counterpart of kamias is karmay or Phylllanthus acidus. A Bicolano friend told me that they call this iba and that they use this in place of kamias. In fact the P. acidus and A. balimbi trees ares hard to distinguish from each other when fruitless. Karmay fruits also look like round version of kamias fruits. In some Tagalog and Bicol households they use the karmay as souring agent for sinigang and paksiw.
In the Visayas, another native tree is used in Visayan sinigang versions. This is batwan or Garcinia binucao, a close relative of the mangosteen. In fact, the fruit resembles a small unripe version of the mangosteen. In the island of Panay, the attractive tree grows tall and abundant, much so that the fruit found its way into the local sinigang dishes and the Visayan palette. A local would readily prefer a batwan sinigang than any cooked with another pampaasim.
There are other trees and plants used as subacid ingredients in Philippine cuisine. I heard that other Garcinia species maybe even better souring agents. Some trees, even their leaves have sub acid components like libas (Spondias pinnata). They may not be as popular as the ones mentioned but this does not mean they fail in comparison in flavour and taste. I hope some of these may get to be discovered as better souring agent alternatives, thus giving us a much better and exciting sinigang to anticipate in the future.