A fermented food is not simply a food with bacteria added to it.
During fermentation, microorganisms such as bacteria or yeasts use components naturally present in the food and transform them into new compounds.
This can change the taste, texture, digestibility and nutritional characteristics of the original food.
What happens during fermentation?
One familiar example is milk.
In yogurt production, bacteria convert some of the milk sugar, or lactose, into lactic acid. The increasing acidity changes the structure of milk proteins and produces the characteristic texture and slightly sour taste of yogurt.
But fermentation can also produce or modify other compounds, including organic acids, peptides and certain vitamins.
The result is a food that can be biologically and nutritionally different from the ingredient from which it started.
Different fermented dairy products are made differently
Even products that begin with milk are not interchangeable.
Natural yogurt is produced using traditional yogurt bacterial cultures.
Greek yogurt is generally yogurt that has been strained or concentrated. It is typically thicker and higher in protein than standard natural yogurt.
Skyr is a cultured Icelandic dairy product that is traditionally closer to a fresh cheese, although it is commonly eaten like yogurt. It is usually high in protein.
Kefir undergoes a different type of fermentation involving a more complex mixture of microorganisms, traditionally including both bacteria and yeasts.
Buttermilk, or maślanka, is different again. Modern cultured buttermilk is generally produced by fermenting milk with selected bacteria.
Their nutritional composition and microbial characteristics can therefore differ substantially.
Do fermented foods always contain live microorganisms?
No.
Some yogurts and kefirs contain live cultures when consumed.
Other fermented foods undergo further processing. Sourdough bread is baked. Cocoa beans are fermented before chocolate production. Some commercial fermented products are pasteurized.
In these cases, few or no live microorganisms may remain.
But fermentation can still leave behind compounds created or transformed by microorganisms during the process.
This is why the potential effects of fermented foods cannot be explained simply by whether they contain “good bacteria.”
Fermentation is a biological transformation of food, not a single nutritional property.
