Is Greek Yogurt Fermented Milk? The Definitive Answer

December 13, 2025 •

3 min read

According to the Yogurt in Nutrition Initiative, fermented milks have been providing essential nutrients and health benefits for centuries. Greek yogurt is, in fact, a type of fermented milk, but with an extra processing step that gives it its signature thick texture and high protein content.

Quick Summary

Greek yogurt is a fermented dairy product made by culturing milk with live bacteria. The key difference is that Greek yogurt is strained after fermentation to remove excess whey, resulting in a thicker consistency and higher protein concentration.

Key Points

Yes, Greek yogurt is fermented milk.: The process of making all yogurt, including Greek, begins with the fermentation of milk using specific bacterial cultures.
Straining is the key difference: After the initial fermentation, Greek yogurt is strained to remove the liquid whey, resulting in a thicker consistency and higher protein content.
Bacteria consume lactose: During fermentation, bacteria convert lactose (milk sugar) into lactic acid, which makes yogurt tangy and easier for some people with lactose intolerance to digest.
Live cultures offer benefits: Greek yogurt contains live and active probiotic cultures that can support digestive and immune health.
Greek yogurt has more concentrated nutrients: The straining process concentrates the protein, but also lowers the amount of certain nutrients like calcium compared to regular yogurt.
The production process controls the outcome: Factors like the type of milk, starter culture, and incubation temperature all influence the final taste and texture.

What is Fermented Milk?

Fermentation is a natural process where microorganisms, like bacteria and yeast, convert sugars into simpler compounds. For milk, this involves adding specific bacterial cultures, which consume the naturally occurring lactose (milk sugar) and produce lactic acid. This increase in acidity causes the milk proteins to coagulate, creating a thicker, tangier product. This process is foundational for many dairy products, including yogurt, kefir, and buttermilk.

The Greek Yogurt Fermentation Process

The production of Greek yogurt begins in the same way as traditional yogurt, with the fermentation of milk.

Pasteurization: The milk is first heated to eliminate any harmful bacteria.
Cooling: The milk is then cooled to an ideal temperature for the starter cultures to thrive, typically around 110°F (43°C).
Culturing: Live bacterial cultures, specifically Streptococcus thermophilus and Lactobacillus bulgaricus, are added to the warm milk.
Incubation: The milk is left to ferment for several hours. During this period, the bacteria convert lactose into lactic acid, giving the yogurt its tangy flavor and gel-like texture.
Straining: This is the crucial step that differentiates Greek yogurt. After fermentation, the yogurt is strained to remove the liquid whey. This can be done traditionally with cloth bags or through modern centrifugal equipment. The straining process is what makes Greek yogurt significantly thicker and tangier than regular yogurt and also concentrates its protein content.

Comparison: Greek Yogurt vs. Other Fermented Milks

While all yogurt is fermented milk, Greek yogurt's straining process gives it a distinct profile. Here is a comparison of Greek yogurt with other popular fermented dairy products.


Feature	Greek Yogurt	Regular Yogurt	Kefir
Fermentation	Bacteria (S. thermophilus, L. bulgaricus)	Bacteria (S. thermophilus, L. bulgaricus)	Kefir grains (SCOBY of bacteria and yeast)
Process	Fermented milk is strained to remove whey.	Fermented milk is cooled without straining.	Fermented with kefir grains; traditionally fermented longer.
Texture	Very thick and creamy.	Thinner, can be spoonable or drinkable.	Drinkable, with a thinner consistency.
Protein	Significantly higher due to straining.	Lower than Greek yogurt.	Variable; can be higher than regular yogurt.
Probiotics	Contains specific cultures; check for live and active cultures.	Contains specific cultures; check for live and active cultures.	Contains a wider variety of strains of bacteria and yeast.
Taste	Tangy and sour due to concentrated lactic acid.	Milder and often sweeter; less tangy.	Very tangy and slightly fizzy due to yeast.

Key Factors Influencing the Final Product

Beyond the fundamental fermentation and straining process, several other factors contribute to the final qualities of Greek yogurt:

Milk Source

The type of milk used, whether from cows, sheep, or goats, affects the final product's flavor and nutritional composition. The initial fat content of the milk also influences the richness and texture.

Starter Culture

The specific strains and ratio of bacterial starter cultures added can influence the flavor, texture, and fermentation speed. While Lactobacillus bulgaricus and Streptococcus thermophilus are required for yogurt, some manufacturers add other probiotic strains for additional health benefits.

Temperature and Incubation Time

Precise temperature control during the incubation period is critical. The incubation time, typically 5-12 hours, allows the bacteria to convert lactose to lactic acid. A longer fermentation time can result in a more tangy, acidic flavor.

Conclusion: Greek Yogurt Is a Refined Fermented Milk

To summarize, Greek yogurt is unequivocally a fermented milk product. It undergoes the same initial fermentation process as regular yogurt, where milk is cultured with specific bacteria to convert lactose into lactic acid. The key distinction lies in the additional step of straining, which removes the whey and concentrates the remaining milk solids. This process yields its characteristic thick, creamy texture and higher protein content, distinguishing it from other fermented dairy products like kefir or traditional unstrained yogurt. So, while all Greek yogurt is fermented milk, not all fermented milk is Greek yogurt.

Disclaimer: The information provided is for educational purposes only and is not medical advice. Consult a healthcare professional for dietary recommendations.

Frequently Asked Questions

The main difference is that Greek yogurt is strained to remove liquid whey after fermentation, which makes it much thicker and gives it a higher protein concentration than regular yogurt.

No, traditional Greek yogurt is strained, while some products labeled "Greek-style" achieve a thick consistency by adding thickening agents or milk protein concentrates, rather than by straining.

Greek yogurt is tangier because the straining process removes some of the lactose while concentrating the lactic acid produced by the fermenting bacteria, resulting in a more intense, sour flavor.

Yes, Greek yogurt contains probiotics, which are beneficial live bacteria resulting from the fermentation process. For the most benefit, look for a 'live and active cultures' seal on the label.

Many people with lactose intolerance find Greek yogurt more tolerable than regular milk. The fermentation and straining processes reduce the lactose content, making it easier to digest.

Both are fermented milk products, but kefir uses a wider variety of bacteria and yeast in 'kefir grains' and is a thinner, drinkable consistency. Greek yogurt is fermented with specific cultures and then strained to be thick and spoonable.

Yes, straining the whey concentrates the protein content but also reduces the calcium and other nutrients that are lost with the liquid.