Fermented dairy products like kefir and yogurt are often grouped together, but they are fundamentally different. Both are created by introducing a culture into milk, which then ferments the natural sugars and transforms the milk’s structure and composition. While both are sources of beneficial microorganisms, their distinct production methods, microbial makeup, and final characteristics mean they serve different purposes in the diet.
How They Are Cultured
The initial step of introducing a culture to milk is where the processes for kefir and yogurt diverge. Kefir is traditionally made using kefir “grains,” which are small, gelatinous matrices of proteins and polysaccharides resembling tiny cauliflower florets. These grains are a symbiotic colony of both bacteria and yeasts (SCOBY) that are added to milk and then strained out, allowing them to be reused. This fermentation occurs at room temperature over a longer period, often 14 to 18 hours, and does not require additional heat.
Yogurt production, in contrast, relies on a specific, standardized starter culture consisting of only a few types of bacteria, most commonly Lactobacillus bulgaricus and Streptococcus thermophilus. These bacteria are added directly to the milk, which is often heated and maintained at a controlled, warmer temperature (thermophilic). The bacteria consume the lactose and produce lactic acid, which causes the milk proteins to curdle and solidify into the familiar thick texture. This process is generally shorter than kefir’s, sometimes taking only two to four hours.
Probiotic Strains and Nutrition
The different culturing methods result in distinct microbial profiles. Kefir contains a far greater diversity of microorganisms, featuring a wide range of bacteria and beneficial yeasts. Traditional homemade kefir can contain over 50 different species, while commercial versions often list 12 or more active strains. The presence of yeasts, such as Saccharomyces cerevisiae, is unique to kefir and contributes to its complex profile.
Yogurt usually contains only a handful of specific strains, primarily the two required for its production. The higher diversity in kefir provides a broader spectrum of microorganisms to the gut microbiome. Kefir also undergoes a more complete fermentation process, breaking down more lactose than yogurt, which often makes it easier to digest for people with lactose sensitivity. Both are sources of nutrients like protein and calcium, but kefir often contains higher levels of B vitamins, such as B12 and K2.
Texture Flavor and Uses
The contrasting fermentation processes dictate the physical and sensory characteristics of the final products. Kefir is a thin, pourable liquid with a consistency similar to buttermilk, making it suitable as a beverage. The yeasts produce small amounts of carbon dioxide and sometimes ethanol, giving kefir a characteristic effervescence and a tangy, yeasty, and acidic flavor profile.
Yogurt is typically thick and spoonable because its proteins coagulate during fermentation, though some varieties are thin and drinkable. Its flavor is generally milder and less tart than kefir. Yogurt is often eaten with a spoon, used as a base for dips, or incorporated into baked goods. Kefir is commonly consumed as a drink on its own or blended into smoothies.