Buttermilk today is cultured low-fat milk — tangy, slightly thick and acidic, with no butter in it. Traditionally it was the thin liquid left over after churning butter. Its acidity is the whole point: it reacts with baking soda (bicarb) to lift biscuits and pancakes, and it tenderises meat in marinades.
Buttermilk turns up all over the old recipe box — biscuits, pancakes, pie, soda bread. But the carton in the store today is not what Granny drank off the churn. Here is what it actually is, why it works, and what to do when the carton is empty.
| Substitute | How to make it | Caveat |
|---|---|---|
| Milk + lemon juice or white vinegar | 1 tbsp acid into 240 ml (1 cup) milk; stand 5-10 min until it curdles slightly | The classic stand-in. Thinner than real buttermilk, but the acid does the job in bakes and marinades |
| Plain yoghurt thinned with milk | 3 parts yoghurt to 1 part milk, whisked smooth | Closest in tang and body |
| Milk + cream of tartar | 240 ml (1 cup) milk + 1¾ tsp cream of tartar | A pinch-hitter for baking only |
Today's buttermilk is cultured milk
The buttermilk you buy now is cultured low-fat milk. Dairies add live cultures to milk and let it ferment, much as yoghurt is made. The result is tangy, slightly thick and acidic. There is no butter in it at all, whatever the name says. In the US it sits in the dairy aisle labelled cultured buttermilk; UK supermarkets sell the same cultured product.
Traditional buttermilk was the churn liquid
The original buttermilk was the thin liquid left behind after churning cream into butter. The fat had gone into the butter, so what remained was thin and light. Grannies drank it fresh and baked with it. Today's cultured version stands in for it — tangier and a touch thicker, but doing the same jobs in the kitchen.
Why the acid matters
Buttermilk's acidity is what earns its place in recipes. Mixed with baking soda (bicarbonate of soda, to British bakers), the acid sets off a fizz of bubbles that lifts biscuits, pancakes and cakes — that is why so many old recipes pair the two. The same acidity tenderises meat in marinades, which is why fried chicken and chicken fried steak so often start with a buttermilk soak. And it brings a gentle tang that plain milk cannot give.
No buttermilk? The lemon-juice trick
Stir 1 tablespoon of lemon juice or white vinegar into 240 ml (1 cup) of milk and let it stand 5 to 10 minutes, until it curdles slightly. That slight curdle is your sign it is ready. It is thinner than the real thing, but the acid does the job in bakes and marinades. Want something with more body? Thin plain yoghurt with milk, 3 parts yoghurt to 1 part milk. And in a pinch for baking only, whisk 1¾ teaspoons of cream of tartar into 240 ml (1 cup) of milk. The table lays out all three.
Where buttermilk shines in our recipe box
Buttermilk is everywhere in old-fashioned baking. Our old-fashioned biscuits and old-fashioned pancakes both lean on the buttermilk and baking soda pairing for their rise. Old-fashioned buttermilk pie turns it into a tangy, custardy filling. And Irish soda bread is the plainest proof of the science: flour, salt, baking soda and buttermilk — nothing else needed for lift.
Questions we get asked
Does buttermilk have butter in it?
No. Modern buttermilk is cultured low-fat milk with no butter in it at all. The name comes from the traditional version — the thin liquid left after churning butter, once the butter had already been taken out.
Is buttermilk just sour milk?
Not quite. Cultured buttermilk is fermented on purpose with live cultures, so its tang is clean and controlled. Milk that has gone off in the fridge is spoiled — do not bake with it. The safe shortcut is milk soured deliberately with lemon juice or vinegar.
What is a good substitute for buttermilk?
Stir 1 tablespoon of lemon juice or white vinegar into 240 ml (1 cup) of milk and let it stand 5 to 10 minutes, until it curdles slightly. Or thin plain yoghurt with milk, 3 parts yoghurt to 1. In a pinch for baking, whisk 1¾ teaspoons of cream of tartar into 240 ml (1 cup) of milk.
Why do recipes call for buttermilk?
For its acid. It reacts with baking soda (bicarb) to lift bakes, it tenderises meat in marinades, and it adds a gentle tang. Plain milk does none of those jobs.
Can you drink buttermilk?
Yes. It is tangy and slightly thick, closer to thin yoghurt than to milk. The traditional churn liquid was an everyday drink, and plenty of kitchens still pour cultured buttermilk chilled.
Is buttermilk low fat?
Yes. Today's cultured buttermilk is made from low-fat milk, so despite the rich-sounding name it is one of the lighter things in the dairy aisle.