Asam: tamarind, asam keping and why they are not the same

Asam simply means sour, and it is doing a lot of work as a word. It appears in the names of several completely different ingredients, which is why recipes calling for "asam" without qualification cause so much confusion, and why substituting one for another produces a dish that tastes almost right and not quite.

Asam jawa

Tamarind, and the one most people mean by default. Sold as a compressed block of dark pulp, usually with seeds and fibre still in it, or as a smoother ready-made paste.

Its sourness is round rather than sharp, with a fruity sweetness underneath and a certain body that thickens whatever it goes into. That body matters: tamarind does not only make a dish sour, it makes it fuller.

To use the block, break off a piece, soak it in warm water for ten minutes, then work it with your fingers until the pulp releases. Strain, press the solids to get everything out, discard the fibre and seeds. What you have is tamarind water, and its strength depends entirely on how much water you used, which is why recipes disagree so wildly on quantities.

Ready-made paste is more consistent and slightly flatter. Perfectly reasonable for weeknight cooking.

Asam keping

Dried slices of a sour fruit, sold as leathery dark brown or blackish pieces. Also called asam gelugor, after the tree.

Completely different in character from tamarind: sharper, cleaner, more austere, with no sweetness and no thickening body. It is sourness on its own, without anything attached.

You use it whole. Two or three slices go into the pot and release their sourness slowly as the dish simmers. Some cooks fish them out before serving, some leave them in. There is no soaking and no straining, which makes it considerably less work than tamarind.

This is what belongs in asam pedas and in most fish curries, and the reason is worth understanding.

Asam boi

Preserved sour plum, salty and intensely sour, and a different category altogether. It belongs in drinks, with fruit, and in some sauces. It is not a cooking souring agent and will not stand in for either of the above.

Worth mentioning only because the shared name catches people out.

Lime

Limau kasturi and limau nipis are the fourth option and behave differently again. Lime is volatile: its aroma disappears within a minute or two of heat, so it contributes sourness when cooked and sourness plus aroma when squeezed at the table.

This is why so many dishes arrive with a wedge on the side rather than the juice already in. The two are not the same addition.

Which to use

• Rendang, sambal, most meat curries — tamarind, for body as well as sourness
• Asam pedas and fish curries — asam keping, for clean acidity
• Rojak and sauces — tamarind, usually
• Finishing anything — lime, at the table
• Drinks and pickles — asam boi

Substituting between them

Not one for one, and not blindly.

Tamarind in place of asam keping makes a fish curry heavier and slightly sweet. If you have no choice, use less than the recipe's sourness suggests and accept a different dish.

Asam keping in place of tamarind leaves a gap where the body should be; the dish tastes thin and sharp. Compensating with a little sugar helps but does not replace it.

Vinegar substitutes for neither. It brings a volatile sharpness that reads as European, and it is obvious in the finished dish.

Storage

Tamarind blocks keep for a year or more in an airtight container, and refrigeration extends that further. They darken over time, which is fine.

Asam keping is already dried and keeps almost indefinitely somewhere dry. If pieces go soft or develop white bloom, humidity has got in; discard them rather than trying to dry them out.