Short answer
US retail buttermilk is a cultured product made by fermenting milk with bacteria, giving it a tangy taste and thicker texture, while regular milk is unfermented and mild. Traditional churned buttermilk, a butter-making byproduct, is not what is sold today. 1 2
Cultured buttermilk is produced by fermenting regular milk with specific bacteria, making it a distinct product rather than a simple subtype.
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At a glance
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| Question | buttermilk | regular milk |
|---|---|---|
| How is it made? | Cultured with bacteria | Unfermented, pasteurized |
| Texture & taste | Thick, tangy | Thin, mild |
What each thing is
Buttermilk. Buttermilk sold in US stores is generally cultured milk fermented with lactic acid bacteria, making it tangy and thicker than ordinary fluid milk. Formulations vary; traditional churned buttermilk is a different historical product. 1 2
Regular milk. Regular milk here means unfermented fluid cow’s milk sold as whole, reduced-fat, low-fat, or fat-free milk. Its fat content depends on the variety. 1 2
Key differences
The main distinction is that buttermilk is intentionally cultured with lactic acid bacteria, resulting in a tangy, acidic flavor and thicker consistency, while regular milk is simply pasteurized and remains sweet and fluid. 1 2
How to tell them apart
You can identify buttermilk by its tangy aroma and thicker texture compared to regular milk. However, labels can be confusing, as ‘buttermilk’ may refer to cultured or, rarely, traditional types, so check for ‘cultured’ on US packaging. 1
Where they overlap
Both buttermilk and regular milk begin as cow’s milk and can be used in baking, but buttermilk’s acidity interacts with leaveners like baking soda, while regular milk does not provide the same chemical reaction or flavor. 1 2
Edge cases
Some recipes or regions may refer to buttermilk as the liquid left after churning butter, but in the US, this traditional byproduct is rarely available; nearly all retail buttermilk is cultured from milk, not churned. 1
Why the distinction exists
Cultured buttermilk is produced to mimic the tang and acidity of traditional churned buttermilk, which was once common in home butter-making. The fermentation process gives modern buttermilk its distinctive properties for baking. 1 2
Common misconceptions
A common misconception is that store-bought buttermilk is the same as the liquid left after making butter. In reality, US buttermilk is almost always a cultured product, not a butter-making byproduct. 1
Examples
A US baker shopping for pancakes sees ‘cultured buttermilk’ in the dairy case, which is tangy and thick. If they use regular milk instead, their pancakes will be less flavorful and may not rise as much if the recipe relies on acidity. 1 2
Sources
Sources checked October 3, 2026.
- King Arthur Baking — What buttermilk is and substitutes. Traditional and cultured buttermilk.
- King Arthur Baking — Buttermilk in baking. Acidity and leavening effect in recipes.