Sourness. A word that conjures up puckered faces and unfriendly dispositions, and a particular fox of Greek origin that famously gave up on some juicy grapes because it couldn’t reach them and had to come up with the excuse that their composition had too much tartaric acid for his taste. That brings us to “acid”, literally meaning “sour” in Latin. Acids are molecules that make hydrogen ions freely available in a solution. We perceive anything acidic as being sour by detecting hydrogen ions on the sides of our tongues, where most of the acid-detecting taste buds reside. Acidity is measured by the pH scale, with a value from 0-7 indicating an acidic environment while 7-14 indicates a basic environment; 7 is the pH of distilled water, the proverbial neutral centre of the taste universe.
Most of the food we eat is mildly acidic, and this is not a bad thing, despite the unfortunate visual image of acids that recall gory scenes from Bollywood films, as a tool used by villains. Acids make us salivate and that makes it easier to digest what we eat. This is why food that is not sour feels heavy in our mouths.
It is also why your grandmother likely squeezes a bit of lime juice into her dal once it’s done cooking. Legumes tend to be bland and heavy, thanks to the resistant starch and protein they contain. A splash of acid livens up the proceedings because that’s what acids do. They brighten flavours, relieve greasiness and overall add a sparkle to the dish you are cooking. To use a sound engineering metaphor, acids act like an equaliser. They balance out sweet, salt, bitter and umami, thus preventing one taste from dominating the proceedings.
You can improve any dish by layering different kinds of acids or, if that word scares you, souring agents. The most common ones in the subcontinent are tamarind and citrus juices. Tamarind adds a heavy, earthy acidity that can be tamed with heat. The longer you cook it, the less sour it becomes. On the other hand, citrus juices must not be cooked; heat makes them develop off-flavours. They are best added at the end of a dish. A good way to make your cooking more interesting is to use different kinds of citrus juices. For a change, try squeezing a bit of orange juice into your dal for a fantastically unique sweet and sour flavour.
Amchur (dried mango powder) is another commonly used acid, adding sourness to dry dishes, where adding liquids might not work. Most fruits are acidic to some degree. The bright green acidity of malic acid in green apples goes fantastically well in many Indian dishes. Throw in green apples into a mixed vegetable gravy to see for yourself.
Yogurt, another acid, has the added advantage of adding a rich creaminess combined with the pleasant sourness of lactic acid to a dish. High heat can cause yogurt to split into unappetising-looking, crumbled curd in your dish, so the trick is to whisk some besan, or gram flour (a pinch of maida, or refined flour, works as well) into the yogurt to strengthen the emulsion before adding it to your dish.
Also read: The science of flavour
One of the most commonly used acids in the rest of the world, but not as common here, is vinegar. Fruit-based vinegars like apple cider and red wine can add fantastic depth along with a sharp sourness that can elevate any dish. Try replacing tamarind or lime with vinegar in a dish to experience this for yourselves.
But acids do much more than just add sourness. In combination with baking soda, they can leaven bread. If you are cooking rajma (red kidney beans) for long periods, adding some acid will prevent the breakdown of pectin in plant cell walls, and prevent the beans from collapsing into mush. They also curdle milk into paneer by denaturing milk proteins and causing them to coagulate into curds.
When you cut vegetables, some plant enzymes cause unpleasant browning and oxidation. This is a defensive mechanism used by plants against anything trying to eat them. Adding a tiny bit of acid to the water in which we store cut vegetables will slow down enzymatic browning. Incidentally, when we walk out in the hot sun, a similar enzymatic reaction happens in our skin, causing us to get tanned.
Acids can also significantly mute the characteristic “fishy” aroma of seafood, caused by the reaction between fatty acids in the fish and a molecule called Trimethylamine N-oxide. This smell can pervade entire houses (and fish markets) for days. Splashing some acid on seafood when cooking it can reduce this.
In the culinary universe, there is no greater demonstration of acid layering than chaat. The quintessential chaat experience combines a spectrum of textures (from the softness of the potatoes to the crunchiness of the puris), the searing heat of the chillies that gives a pleasurable endorphin rush, all brought together by a spectacular orchestral symphony of acids—the earthy base acidity of tamarind, the fresh and mild acidity of tomatoes, the complex dry acidity of amchur and the finishing high note of lime juice. It is a disco party of flavours in your mouth, and you can thank the acid symphony orchestra for the magic.
So, don’t be the presumptuous Greek fox that left the sour grapes behind. Make sour grape juice and add it to your dal—you won’t be disappointed.
Krish Ashok is the author of Masala Lab: The Science Of Indian Cooking. @krishashok