The best part about unbearably hot summer weather is you get to enjoy nimbu soda. That’s not to say you can’t drink nimbu soda in the winter, or the spring, or the fall; it’s essentially citrus juice and soda water, rounded out with a little sugar and some salt. You can drink it any time at all.
But nimbu soda is best when you’re so hot you can barely think, when your body is sheathed in a thin film of warm sweat, when the exterior of the glass you hold in your hand, filled just moments before, is also entirely wet from the condensation of the swampy air. There’s no better time to drink nimbu soda than when the weather approximates the sweltering summers I spent in New Delhi, India, as a kid, when temperature would regularly be at or over 100 degrees.
Nimbu soda is an effervescent variation on nimbu pani, a citrus-and-water drink sold practically everywhere. My parents, overly cautious as expats typically are, warned us against patronizing the nimbu pani wallahs you’d find on the streets, with their huge cuboid metal carts filled with ice water, pyramids of limes arranged on top. Instead, if we wanted to drink nimbu pani or soda, we were told to make it ourselves at home: a little lime juice in a tall glass; a pinch of kala namak, or black salt, or a pinch of sugar, or both, depending on your preferences; ice; and soda to fill the glass to the top. I’d stir it with my finger and drink it in a few long gulps.
As you can see, a recipe isn’t particularly necessary for such a simple drink, although there are ways to make it a little more complicated. When we’d order it in hotel restaurants—the pleasure of nimbu soda on a hot day while blessed with extremely effective central air conditioning, which we did not then have nor do I now, is a luxury I’ll always associate with going to lunch with visitors at the Hyatt Regency off the Ring Road—the drink would come with a little carafe of simple syrup, so you could sweeten it as much as you like. If you have, say, some lemon or lime syrup in your fridge, feel free to use a little in place of the sugar.
Like any simple concoction, tiny, optional details like that can make a big difference. If you just dump all the ingredients in a glass, your nimbu soda will be fine, but if you put a little thought into it, it can be better than fine. In this recipe, instead of simple syrup, I pre-mix the salt and sugar with the lime juice until dissolved and then add the soda. That’s because you don’t want to dissolve any sugar or salt in a carbonated beverage, since the solid provides nucleation sites leading to a more rapid loss in carbonation.
The ice presents a similar concern: It’s best to start with wet ice, or ice that’s been wet with water and then drained, since pouring a carbonated beverage over ice straight from the freezer will result in an immediate loss of a lot of those pleasing bubbles. Like the crystals of sugar and salt, ice straight from the freezer has more surface imperfections that can provide escape routes for the carbon dioxide in the liquid; wetting the ice smooths those imperfections out. It’s the same physical process that’s responsible for all those videos online of people dunking Mentos into Coke bottles: fun to watch but bad for enjoying the soda.
So the best way to get salt, sugar, and ice into this mixed carbonated drink is to wet your ice in the serving glass, which also chills the glass, dissolve the solids in the citrus juice, and then start making the drink.
As the nimbu pani NPR article linked to above notes, you can play around with seasoning the drink using a mix of spices or with a spice mix if you have some on-hand: a chaat masala wouldn’t be out of place. I generally prefer to keep it as simple as possible. And if you don’t have kala namak, you can always just use plain old salt, although the slight sulfurous notes of kala namak give the drink an expansive dimension that sets it apart from other citrusy drinks. The amounts given below are solely based on my preference—more salty than sweet, the sugar serving mostly to counterbalance some of the sourness from the lime—but you can adjust the ratios according to your tastes.
So there it is: Go out, get sweaty, and make yourself a nimbu soda. For maximum pleasure, drink it while baking in the full light of a brutal noonday summer sun.