Curd vs Buttermilk: What Changes When You Churn or Thin Your Dahi?

Quick Answer

Curd and buttermilk are closer relatives than rivals. Curd is more concentrated than chaas made by thinning it with water. Chaas contributes fluid and makes a refreshing drink. Both can contain live cultures, but neither is automatically a proven probiotic or lactose-free. The milk, method, portion and storage all matter.

As a nutritionist and a South Indian, curd and buttermilk are staples in my daily diet. There isn’t a day without them. Curd rice is something I enjoy every day. It could be as simple as curd with rice, a little pickle and papad, or curd rice with a tadka of cumin, curry leaves, garlic and urad dal, with pomegranate for the garnish.

For me, it’s a wholesome, refreshing dish that satisfies my taste buds. The curd can bring live cultures, while the dal, fruit and herbs add plant ingredients to the bowl. At home, we also make two kinds of buttermilk.

Two Things Called Buttermilk

Before comparing anything, it helps to know that ‘buttermilk’ in India can mean two slightly different drinks.

Traditional buttermilk is what’s left after curd is churned to separate out the butter. Removing the butter takes away much of the fat, leaving a thinner, tangy liquid. In homes that still make makhan, this is the buttermilk that comes with it.

Everyday buttermilk, often called chaas, is simply curd whisked with water, usually with salt, roasted jeera, perhaps some ginger, curry leaves or pudina. Whisking and adding water do not remove butter: the curd’s fat is spread through a larger volume.

The product sold as ‘cultured buttermilk’ in many Western recipes is different again, usually made by adding cultures to milk. It isn’t necessarily the same as homemade chaas.

Curd and Buttermilk Side by Side

This compares plain curd with chaas made by whisking that same curd with water. Traditional buttermilk left after butter-making has a different composition.

Protein and Fullness

Curd is the more concentrated food. Chaas made by adding water contains less protein per spoonful or equal weight, but the amount in your glass depends on how much curd went into it. A bowl and a glass aren’t fixed nutritional measures.

Whisk a bowl of curd with water and drink the whole batch, and you still get the protein from that bowl. Divide it among several glasses, and each glass gets a share.

Curd is a useful way to add protein alongside a paratha, rice, dal or sabzi. Chaas is the lighter companion when you want a drink. For packaged versions, compare the protein per 100 g or 100 ml and check the serving size.

Live Cultures and Packaged Versions

Chaas made from curd starts with the curd’s cultures. Adding water spreads them through a larger volume; it doesn’t create more. Cooking curd in kadhi or mor kuzhambu can destroy live cultures, so don’t count on those dishes as a source of them.

I prefer simple homemade curd and chaas for everyday use, with ingredients and seasoning I can choose. But homemade doesn’t guarantee a particular bacterial count or health benefit. Live cultures and probiotics aren’t interchangeable terms: a probiotic claim needs identified live microorganisms and evidence of a benefit at the amount consumed.

When buying either, look for information about live cultures and whether the product was heated after fermentation. FSSAI’s fermented-milk standards distinguish heat-treated products from those expected to retain viable starter cultures. Don’t assume that every carton lacks live cultures, or that refrigeration alone proves they are present. Follow the pack’s storage and use-by instructions.

Heating the milk before adding the starter is a different step: the cultures are added afterwards.

Lactose and Your Own Tolerance

When milk ferments into curd, bacteria use some of its lactose. Certain live yoghurt cultures also supply an enzyme that helps break down lactose during digestion.

The European Food Safety Authority’s assessment found that live yoghurt cultures improve digestion of the lactose in yoghurt in people with lactose maldigestion. That finding concerns yoghurt containing the standard starter cultures, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, in sufficient numbers. It isn’t a guarantee for every batch of homemade dahi or every glass of chaas.

Homemade dahi’s cultures vary, and both curd and buttermilk still contain lactose. Adding water lowers its concentration but doesn’t reduce the total lactose from the curd you used.

Some people with lactose intolerance tolerate yoghurt better than milk. If that is your concern, try a small amount of curd with a meal and see how you feel. Lactose-free dairy is another option. A milk allergy is different: dairy curd and buttermilk still contain milk proteins and should be avoided if you have one.

The Post-Meal Glass and Curd at Night

A glass of chaas after lunch is a familiar food habit in many Indian homes. It can be refreshing, especially on a hot day. If a heavy meal has already left you feeling full, let your appetite decide whether you want a glass; you don’t need to force one down for digestion.

Many households also avoid curd at night. If curd with dinner sits well with you, the time of day alone isn’t a reason to give it up. If you have reflux, pay attention to your own triggers and the size and timing of the meal. The NHS advises leaving three to four hours between eating and bedtime. Thinning curd into chaas doesn’t automatically make it more comfortable for everyone.

And Lassi?

Lassi is also made from curd, often with less water than chaas, though recipes vary. Its protein depends on the curd used and the serving size. Sweet lassi can bring a substantial amount of added sugar; plain, unsweetened lassi is an everyday alternative. With salted lassi, keep an eye on the salt, just as you would with masala chaas.

Two Buttermilk Favourites from My Kitchen

In my South Indian home, these are two versions we enjoy:

Ragi Buttermilk or Ragi Ambli

This is a refreshing drink we make in summer. First, cook ragi flour with water to make a thin porridge, then cool it before mixing it with the curd. Flour needs thorough cooking; don’t stir raw ragi flour into a ready-to-drink glass.

We whisk curd with safe drinking water, add chopped onions, coriander and seasonings such as black salt, jeera powder and chaat masala, then mix in the thin, cooked and cooled ragi mixture. Stir everything well and enjoy it chilled.

Masala Chaas or Majjige

We grind a small green chilli, two or three garlic cloves, a small piece of ginger, a few curry leaves, mint leaves and coriander into a thin paste. To this, we add whisked curd and water until it is thin and flowy, then season to taste with salt, chaat masala and jeera powder. Chill it and enjoy it during the day. Adjust the chilli and garlic to what suits you.

Making Both Well at Home

To set curd at home, start with pasteurised milk. Bring it to a boil, then let it cool to lukewarm before adding a little fresh plain curd with live cultures. Use clean utensils and a clean, covered container. Leave it undisturbed until set, then refrigerate promptly. If using a commercial starter, follow its temperature and timing instructions.

Use a fresh starter rather than a very old batch. Refrigeration slows further souring once the curd has set.

For chaas, use safe drinking water and washed herbs, make it fresh and keep it refrigerated until serving. If you make makhan at home, the liquid left after churning can be used as traditional buttermilk; keep that chilled too.

For finished curd, chaas and curd rice, follow the FDA’s storage guidance for perishable foods: refrigerate at 4°C or below and don’t leave them out for more than two hours, or one hour when the temperature is above 32°C.

A Word on Salt

Masala chaas usually contains salt, and black salt and salt-containing chaat masala add to the total too. If you’ve been advised to limit sodium, check packaged drinks’ labels or make yours with less salt. Jeera, ginger, pudina and coriander can bring plenty of flavour.

Which to Choose and When

Choose curd when you want a spoonable accompaniment that adds protein to a meal: beside a paratha, in raita or stirred into curd rice. Choose chaas when you want a refreshing drink, adjusting the curd-to-water ratio and seasoning to your taste.

For live cultures, preparation and storage matter more than whether you use a bowl or a glass. At my table, there is room for both.

Sources

• EFSA Panel on Dietetic Products, Nutrition and Allergies. Live yoghurt cultures and improved lactose digestion. EFSA Journal. 2010;8(10):1763; corrected 2011.
• Marco ML and colleagues. ISAPP consensus statement on fermented foods. Nature Reviews Gastroenterology & Hepatology. 2021;18:196–208.
• FSSAI. Dairy products and analogues, version 2, 4 November 2024. Section 2.1.13: Fermented milk products.
• IGNOU. Dairy technology: Definition, standards and principle of butter making.
• NIDDK. Eating, diet and nutrition for lactose intolerance.
• NIDDK. Definition and facts for lactose intolerance, including the distinction from milk allergy.
• NHS. Heartburn and acid reflux.
• Utah State University Extension. Homemade fermented yogurt.
• US FDA. Flour is a raw food and other safety facts.
• US FDA. Are you storing food safely?

Disclaimer: This article provides general information and is not a substitute for personalised medical advice, diagnosis or treatment. If symptoms continue, are severe, or keep coming back, it’s worth speaking to a doctor. If you have a milk allergy, avoid dairy curd and buttermilk. If you have lactose intolerance or have been advised to limit sodium, follow your doctor’s or dietitian’s guidance.