Yes, store-bought buttermilk is fermented—but not in the way you might think

November 28, 2025 •

3 min read

While traditional buttermilk is a byproduct of churning butter, the tangy, thick liquid found in modern grocery stores is produced differently. So, is store-bought buttermilk fermented? Yes, it is a cultured and fermented dairy product, but the process has been modernized for consistent results.

Quick Summary

The cultured buttermilk sold commercially is created by adding live bacteria to pasteurized milk, causing it to ferment. This process is distinct from the traditional byproduct of butter-making, resulting in a thick, tangy product. The controlled fermentation gives it a consistent flavor and texture for baking and cooking.

Key Points

Modern Production: Store-bought buttermilk is a "cultured" product, intentionally fermented by adding bacteria to pasteurized milk.
Not a Byproduct: Unlike traditional buttermilk, it is not the leftover liquid from churning butter.
Live Cultures: The fermentation process uses active cultures of lactic acid bacteria, similar to yogurt.
Tang and Thickness: Lactic acid production gives buttermilk its characteristic tangy flavor and thick, creamy consistency.
Baking Benefits: The acidity is crucial for leavening baked goods when combined with baking soda, resulting in a light texture.
Not a Substitute: A homemade 'soured milk' substitute is not fermented and lacks the probiotic benefits and consistent properties of true cultured buttermilk.

The Truth About Your Grocer's Buttermilk

For many, the word "buttermilk" conjures images of old-fashioned homesteads and churning butter. In that traditional context, buttermilk was indeed the low-fat liquid leftover after butter was churned from cultured, or ripened, cream. It was thinner than today's product, yet still tangy from the natural fermentation process initiated by ambient bacteria.

However, the vast majority of buttermilk sold today bears little resemblance to this historical version. What you find in the refrigerated aisle is cultured buttermilk, a product that is specifically manufactured through a controlled fermentation process. This modern approach ensures a consistent product that is perfect for use in recipes, from biscuits and pancakes to marinades and salad dressings.

How Cultured Buttermilk is Made

Commercial dairies produce cultured buttermilk by following a specific, reliable process:

Preparation: Fresh milk (typically low-fat) is first pasteurized and homogenized to ensure its safety and prevent separation.
Inoculation: Active cultures of lactic-acid-producing bacteria, such as Lactococcus lactis, are added to the prepared milk.
Fermentation: The inoculated milk is heated and held at a specific temperature for several hours, allowing the bacteria to consume the lactose (milk sugar).
Thickening and Flavor: As the bacteria ferment the lactose, they produce lactic acid. This process lowers the pH, causing the milk protein casein to coagulate and thicken the mixture. It is this lactic acid that also imparts the characteristic tangy, slightly sour flavor.

Buttermilk and Your Gut Health

Because cultured buttermilk is a fermented dairy product with live cultures, it can offer gut health benefits similar to other probiotic foods like yogurt and kefir. While the pasteurization process can kill some of the beneficial bacteria, the culturing process reintroduces them. These probiotics can help maintain a healthy balance of gut flora, which aids in digestion and can support the immune system.

Unlike a quick homemade substitute made with milk and vinegar or lemon juice, true cultured buttermilk has undergone a biological transformation. The added acid in a DIY version simply curdles the milk; it doesn't break down the lactose or introduce beneficial bacteria in the same way, and it won't produce the same depth of flavor or probiotic content.

The Role of Buttermilk in Baking

Buttermilk is a hero ingredient in baking, and its fermentation is the key to its success. The acidity of cultured buttermilk reacts with alkaline baking soda to produce carbon dioxide gas. This reaction creates bubbles that help leaven baked goods, resulting in a lighter, fluffier texture in everything from pancakes to cornbread.

Conversely, substituting with regular milk in recipes designed for buttermilk can lead to a denser, flatter result because the leavening reaction won't be properly activated. The tanginess also adds a layer of flavor complexity that is difficult to replicate with other ingredients.

Comparison: Cultured vs. Traditional Buttermilk


Feature	Store-Bought (Cultured) Buttermilk	Traditional Buttermilk	Homemade Substitute (Soured Milk)
Source	Pasteurized milk + added live cultures	Liquid leftover from churning butter	Milk + acidic ingredient (vinegar/lemon juice)
Consistency	Thick, creamy due to coagulation	Thin, watery (fat has been removed)	Curdled, with separated solids and whey
Flavor Profile	Tangy, mildly sour, consistent	Slightly tangy, but less pronounced	Primarily sour from the added acid
Fermentation	Yes, controlled fermentation with specific bacteria	Yes, natural fermentation of cream (now rare)	No, chemical curdling, not biological fermentation
Probiotics	Yes, contains live, active cultures	Often none (pasteurization) or variable (raw milk)	No, no bacterial cultures are added
Best For...	Baking, marinades, dressings	Not widely available for purchase	Emergency baking substitute only

Conclusion: The Modern Fermented Marvel

In short, is store-bought buttermilk fermented? Yes, absolutely. It is a carefully cultured product that leverages the power of lactic acid bacteria to create a consistent, tangy ingredient. While it differs from the old-fashioned version that was a byproduct of butter-making, this controlled fermentation gives it the unique properties that make it an indispensable tool for bakers and cooks. Understanding this modern process can help you appreciate its culinary contributions and even explore the benefits of its live cultures.

For more information on the benefits and uses of fermented foods like buttermilk, you can consult reputable health and food science resources like Healthline.

Frequently Asked Questions

Cultured buttermilk is made by adding specific live bacterial cultures, such as Lactococcus lactis, to pasteurized and homogenized milk. The mixture is then allowed to ferment for several hours, which produces lactic acid, creating its thick, tangy properties.

No, they are different. Traditional buttermilk was the thin, watery liquid leftover from churning butter. Modern cultured buttermilk is a thicker, specifically fermented product made from milk and added bacteria.

Yes, since it is a fermented dairy product with live, active cultures, it contains probiotics. These beneficial bacteria are good for gut health and digestion.

A homemade substitute (milk + vinegar or lemon juice) can be used in a pinch for recipes where acidity is needed, but it's not a fermented product. It lacks the same flavor, thickness, and probiotic content of true cultured buttermilk.

The acidity of buttermilk is essential for activating baking soda, which produces carbon dioxide bubbles that leaven baked goods. This results in a tender and fluffy texture, which is difficult to achieve with regular milk.

Yes, buttermilk is a nutritious drink. It is rich in vitamins and minerals like calcium and vitamin B12 and is low in fat. The live cultures also aid in digestion.

Store buttermilk in the refrigerator. Because it is fermented, it generally lasts longer than regular milk, often 1-2 weeks past the expiration date on the carton. If it has a foul odor or visible mold, it should be discarded.