Kefir, yoghurt, sauerkraut and sourdough bread have one thing in common: micro-organisms play a part in making them. But behind the term ‘fermented’, the processes and characteristics of the products differ. Here’s how to tell them apart without confusing live cultures, probiotics and health claims.
How does milk become kefir?
Traditional milk kefir is made by bringing milk into contact with kefir grains. Despite their name, these grains are not cereals: they are communities of bacteria and yeasts combined in a particular structure. During fermentation, the micro-organisms transform some of the milk’s sugars and produce, among other things, lactic acid.
The drink thus develops a tangy flavour, a consistency that may thicken and, depending on the process, a slight fizz. The result varies according to the culture used, the temperature and the duration. Not all products sold as kefir therefore necessarily have the same microbiological composition.
Yoghurt is also fermented milk. However, traditional production relies on specific bacteria, whereas traditional kefir combines bacteria and yeasts. The distinction lies above all in the production process, not in a ranking of one food as ‘good’ and another as ‘bad’.
A technique used in many cuisines
In sauerkraut, lactic acid bacteria transform the cabbage. In sourdough, bacteria and yeasts take part in fermentation before baking. Fermented soya gives rise to products as different as miso and tempeh.
An international consensus of specialists, published in the journal *Nature Reviews Gastroenterology & Hepatology*, defines fermented foods as ingredients transformed through microbial growth and enzymatic reactions. This distinction makes it possible to tell a genuinely fermented vegetable from one simply preserved in vinegar.
Depending on the recipe, fermentation affects texture, aromas, acidity or shelf life. Its culinary value is therefore tangible, even when the food is not presented as beneficial to health.
‘Fermented’ does not necessarily mean ‘probiotic’
This is a common misconception. A fermented food may no longer contain living micro-organisms when it is eaten: baking sourdough bread, for example, inactivates those that contributed to the fermentation of the dough.
Conversely, even when a food contains live cultures, they are not automatically probiotics. To qualify, identified micro-organisms must provide a demonstrated health benefit at an appropriate dose. The US National Institutes of Health point out that not all fermented foods meet this definition.
This does not detract from their gastronomic value. It simply means that health effects must be assessed product by product and cannot be inferred from a general claim about the microbiome.
Choosing kefir in the shop
The label is the best place to start. Checking the ingredients list helps distinguish a plain drink from a flavoured or sweetened version. Information about the cultures, when shown on the packaging, can help you understand the process used.
You should also check the storage instructions and follow them. For homemade preparations, fermentation is no absolute guarantee of safety: clean utensils, the quality of the milk and the condition of the cultures remain essential.
Finally, milk kefir remains a dairy product. Fermentation may alter some of the lactose, but it does not guarantee its complete removal and does not make the drink suitable for people allergic to milk proteins.
A culinary curiosity that deserves better than slogans
Kefir invites us to rediscover an ancient way of transforming food: here, the taste depends as much on the work of micro-organisms as on the choice of ingredients. Science continues to study the links between fermented foods and health, but that does not justify presenting kefir as a universal remedy.
For consumers, the most useful approach remains simple: understand what you are buying, appreciate the differences between preparations and include these products in a varied diet if you enjoy them and they suit you.
Sources
- International scientific consensus on fermented foods, *Nature Reviews Gastroenterology & Hepatology*.
- Probiotics — Consumer, National Institutes of Health.
- Understanding the scientific definition of fermented foods, ISAPP.
