Draft
What is the difference between curd, kefir and yoghurt?
Curd, yoghurt and kefir are all milk turned tangy by live cultures. What sets them apart is which tiny organisms do the work, and what you get at the end.
If you have ever wondered how three milky foods can taste so different, the answer is in the cultures. Curd, yoghurt and kefir all start as milk and all rely on live microbes to thicken and sour it. Each uses a different cast of organisms, and that shapes the texture, the tang, and the feel in your mouth.
They all begin the same way
Each one is milk that live cultures have fermented. The microbes feed on the milk sugar and turn it into lactic acid, which sets the milk and gives it that gentle sourness. The food scientists at NCCIH describe these live microorganisms, found in yoghurt and other fermented foods, as probiotics. Some research suggests fermented milks like these may support the balance of bacteria in the gut, though what each person notices varies.
Curd, yoghurt and kefir, one by one
Curd, known as dahi across the Indian subcontinent (dahi simply means the traditional set yoghurt of the region), is usually made by stirring a spoon of an earlier batch into warm milk and letting it set overnight. The exact mix of cultures can shift a little from kitchen to kitchen, which is part of why home-set dahi tastes the way it does.
Yoghurt, in the food-science sense, is set by two named cultures working together: Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. They are warmth-loving bacteria, and that pairing gives yoghurt its familiar thick, smooth, mildly sour character.
Kefir is the lively one. It is fermented with kefir grains, which are not grains at all but small soft clusters holding a whole community of bacteria and yeasts living together. The yeasts add a little fizz, so kefir comes out thinner, pourable, and slightly effervescent, with a tang of its own.
So which should you reach for?
There is no single answer, and there does not need to be. They are three takes on the same simple idea: milk, time, and live cultures. A thick spoonful of curd, a smooth bowl of yoghurt, and a fizzy glass of kefir each have their own place. You could try them across a week and notice which one your body, and your day, take to. That noticing is the real practice.