How Many CFU Are in a Serving of Kefir?

November 20, 2025 •

4 min read

According to research, a single cup of kefir can contain anywhere from 10 billion to upwards of 50 billion Colony Forming Units (CFU) of beneficial bacteria and yeast, though some estimates are even higher depending on various factors. Understanding how many CFU are in a serving of kefir requires a look at the product's fermentation, preparation, and storage.

Quick Summary

The CFU count in a serving of kefir varies widely based on whether it is homemade or store-bought, fermentation duration, and temperature. Factors like milk type, kefir grain quality, and storage conditions also significantly influence the final probiotic concentration.

Key Points

CFU counts vary widely: The Colony Forming Unit (CFU) content in kefir can range from billions to trillions per serving, influenced by preparation methods.
Homemade vs. Store-bought: Homemade kefir made with active grains typically offers higher and more diverse CFU counts compared to standardized commercial products.
Fermentation affects CFU: Factors like fermentation duration, temperature, and the ratio of grains to milk significantly impact the final probiotic concentration.
Storage is crucial: Proper refrigerated storage is necessary to maintain the viability and potency of kefir's live and active cultures.
Diversity over quantity: While a high CFU count is beneficial, the wide diversity of probiotic strains in traditional kefir is equally important for promoting gut health.
Maximizing homemade kefir: To maximize CFU, use high-quality, active grains, maintain the right temperature, and aim for a 12-24 hour fermentation period.

The Wide Range of Probiotic Counts in Kefir

Determining an exact number for how many CFU are in a serving of kefir is complex because the probiotic count is not fixed. Unlike a manufactured supplement with a stated dosage, kefir is a fermented food with a living and dynamic microbiome. The CFU count can fluctuate from billions to trillions, influenced by numerous variables. Understanding this variability is key to appreciating kefir as a powerful and natural source of probiotics.

What Is a CFU?

CFU stands for Colony Forming Unit, a term used by microbiologists to quantify the number of viable microorganisms, such as bacteria and yeast, in a sample. One CFU represents a single cell or a cluster of cells capable of multiplying to form a visible colony. In the context of kefir, the CFU count indicates the potency and diversity of the probiotic cultures present.

Factors Influencing the CFU Count

Several factors can dramatically alter the CFU count in a serving of kefir. These include:

Fermentation Time and Temperature: The duration and temperature of fermentation play a critical role. Longer fermentation times (up to 48 hours) at warmer temperatures (20–25 °C) can lead to higher CFU counts as the microorganisms multiply. However, after a certain point, the count may plateau and even begin to decline.
Kefir Grains and Milk Ratio: The ratio of kefir grains to milk affects the speed and potency of fermentation. A higher grain-to-milk ratio can result in faster fermentation and potentially higher initial CFU counts, though the final profile may vary.
Homemade vs. Store-Bought: Homemade kefir, made with fresh, active kefir grains, often contains a higher and more diverse range of probiotic strains and CFUs than many commercial products. Commercial brands must process and store kefir, which can sometimes reduce the final probiotic count, though reputable brands like Lifeway clearly state their CFU content.
Type of Milk: The type of milk used (e.g., cow, goat, skim, or whole) affects the nutrient availability for the microorganisms. Whole milk, for instance, has been shown to produce a higher CFU count in some studies compared to low-fat milk.
Storage Conditions: After fermentation, proper refrigerated storage is essential to maintain the CFU count. Continuous metabolic activity can occur in refrigerated kefir, which can cause slight changes over time, but cold temperatures slow this process significantly.

Homemade Kefir vs. Store-Bought Kefir

For those serious about maximizing their probiotic intake, understanding the difference between homemade and commercial kefir is important. Homemade kefir offers the highest potential for diversity and potency, while store-bought kefir provides consistency and convenience.


Feature	Homemade Kefir	Store-Bought Kefir
CFU Count	Highly variable, often reaching hundreds of billions to trillions per serving due to fresh, active grains.	Standardized and guaranteed CFU count, often 25-50 billion per serving.
Probiotic Diversity	Contains a wider and more diverse array of bacteria and yeast strains, including unique kefir-specific bacteria.	Typically contains a smaller, standardized selection of specific bacterial strains, often listed on the label.
Taste Profile	More complex and tangy flavor profile that can be customized based on fermentation time and conditions.	Flavor is consistent, often with added sugars or flavorings, and may be less tangy than homemade versions.
Convenience	Requires active management and daily attention to the fermentation process.	Ready-to-drink and widely available, requiring no preparation.
Cost	Cost-effective over the long term, as kefir grains can be reused indefinitely.	Generally more expensive per serving, but with guaranteed results.

How to Maximize CFU in Homemade Kefir

To ensure your homemade kefir contains a robust CFU count, follow these best practices:

Use Active Kefir Grains: Start with high-quality, active kefir grains, which are a complex symbiotic culture of bacteria and yeast (SCOBY).
Maintain the Right Temperature: Ferment at a consistent room temperature (around 20-25 °C). Avoid extremes of heat or cold, as they can stress the grains.
Optimal Fermentation Time: Aim for 12 to 24 hours of fermentation. The longer the ferment, the tangier and more acidic the kefir, which can impact the bacterial profile.
Proper Grain-to-Milk Ratio: A standard recommendation is 1-2 tablespoons of grains per 2 cups of milk. Adjusting this ratio can change the fermentation speed.
Use Good Quality Milk: Opt for whole, pasteurized milk, as its nutrients support a thriving microbial population. Avoid using ultra-pasteurized (UHT) milk, which may not ferment correctly due to altered protein structures.

Health Benefits of a High CFU Count

The high and diverse CFU count in kefir is what gives it its potent health benefits. A robust population of beneficial microbes can help support digestion, boost immune function, and contribute to overall gut health. The specific probiotic strains, such as Lactobacillus kefiri and Lactobacillus acidophilus, work synergistically with the yeasts to create a powerful fermented food that can aid the body in several ways. For example, the high probiotic diversity helps create a balanced gut microbiome, which is foundational for overall well-being.

Conclusion

There is no single answer to the question of how many CFU are in a serving of kefir due to the dynamic nature of fermentation. The probiotic count can range from dozens of billions in commercial products to hundreds of billions or even trillions in homemade versions, influenced by factors like fermentation time, temperature, and milk type. For consistent results, a store-bought brand with a guaranteed CFU count is a reliable option. However, for maximum probiotic diversity and potency, a homemade batch using fresh kefir grains is the superior choice. Regardless of the method, including kefir in your diet offers a fantastic way to consume a rich, living source of probiotics.

Further Reading: For more on the science behind fermented foods, see The Art of Fermentation by Sandor Ellix Katz.

Frequently Asked Questions

A good CFU count for store-bought kefir is typically 25 to 50 billion per serving, as guaranteed by the manufacturer. For homemade kefir, which is not standardized, a 'good' count could be much higher, potentially reaching into the hundreds of billions or more, as it contains a wider variety of strains and is freshly made.

While a higher CFU count generally indicates a more potent probiotic source, it's not the only factor. The diversity of the strains is also crucial. Traditional kefir is valued for its wide variety of bacteria and yeast strains, which may offer broader health benefits than a product with a high count of only a few strains.

Yes, the CFU count in kefir can decrease over time, especially during storage. While refrigerated temperatures slow down the metabolic activity, the count will naturally peak and then begin to fall. Consuming kefir before its 'sell-by' date helps ensure maximum probiotic potency.

Fermentation time directly affects the CFU count. Initially, the microorganisms multiply, increasing the count. However, if fermented for too long, the environment can become too acidic, causing the bacteria to die off and the count to decrease. A typical 24-hour fermentation is a good balance for both potency and flavor.

Milk kefir is generally considered the 'powerhouse' of probiotics and typically contains a significantly higher CFU count than water kefir. While water kefir has a respectable CFU count (ranging from a billion to 30+ billion per cup), milk kefir can often exceed this by a large margin.

Reputable brands typically guarantee the CFU count 'at the time of manufacture' or 'by the best-by date'. However, the actual count may fluctuate due to storage and temperature. For the most reliable count, stick to well-known brands that provide specific numbers.

The most effective way to maximize your CFU intake is by making homemade kefir using fresh, active kefir grains. Consistent, controlled fermentation conditions (around 24 hours at room temperature) will ensure a robust and diverse culture. Drinking it soon after straining also ensures the highest possible CFU count.