What is fermentation?

Sauerkraut and pickles, yogurt and cheese, wine and beer, miso and tempeh, salami and fish sauce, coffee and chocolate – sound familiar?  These foods are the outcome of microbial transformation, or what we know as fermentation.

But how can such a broad range of foods, with vastly different flavour and textures across many different food groups, fit under the umbrella of fermentation? 

Well a complex range of foods requires getting clear on what fermentation actually means 

Fermentation meaning

Fermentation is the transformation of food in a controlled environment by bacteria, fungi, and yeast into a range of value-added end products. This happens as these microorganisms utilize carbohydrates within all types of food for growth and activity (1, 2). 

The reason cabbage becomes sauerkraut, not a jar of rot, has to do with the right conditions for growth of the right microbes. 

Left to chance, any old microbe will grow. Getting microbes to grow is not the issue. Just leave cabbage on the counter for a couple weeks; you’ll see microbes in action but it won’t magically make sauerkraut. 

Getting the right microbes to grow for a certain end product is where fermentation comes in. 

Creating safe, edible, and appealing fermented foods takes guiding microbes down the right pathway rather than the default – rot. 

Types of fermentation microorganisms 

As the definition states, a wide variety of microorganisms can process carbohydrates into products that give fermented food unique flavour and texture. Certain flavours, texture, or characteristics often indicate one of the following fermentation microbes at work:

• lactic acid bacteria
• acetic acid bacteria 
• yeast
• mold

For instance, the characteristic sour tang in yogurt and sauerkraut is thanks to lactic acid bacteria. 

Hints of vinegar in kombucha is a sign of acetic acid-producing bacteria. 

Air pockets in sourdough bread and carbonation of fermented drinks has yeast written all over it. 

And we have mold to highlight for behind the scene fermentation of natto, miso, tempeh, and soy sauce. 

Fermented foods are never fermented by one microbial species. One or more may dominate at the end, but often there is a distinct succession of microbes that create an increasingly hostile environment to inhibit spoilage microbes. 

Sources of microbes

Microbes are at the heart of fermentation, and getting the right flavour and texture relies on adequate amounts of the right ones. This leads us to sources of microbes. 

Native to food ingredients 

Fermentation microorganisms can be natural or added. 

All foods have microbes roaming its surface. The trick is for fermentation microbes to win the race for dominance over spoilage microbes, that is, to outcompete other microbes for nutrients and space such that they multiply at a faster rate and take the majority. 

Modifying the environment gives fermentation microbes the upper edge.

For example, lactic acid bacteria are the key microbes in fermented vegetables, though they are the microbial minority on freshly picked vegetables. 

Simply adding a little salt and removing oxygen from the picture tweaks the environment in favour of salt-tolerant lactic acid bacteria. By contrast high salt and an anaerobic atmosphere are hostile to spoilage microbes. 

Therefore, lactic acid bacteria go on to ferment many vegetables into what we know as sauerkraut, kimchi, and pickles, while leaving spoilage microbes to fizzle out.

Starter culture

Wild fermentation is fine for foods that can culture the right quantities of the right microbes in the right conditions. But for foods that don’t, we need an added culture.

Starter cultures deliver specific species of microbes in high amounts. Kefir grains, kombucha SCOBY, and yogurt and cheese cultures are examples. Starter cultures provide predictable characteristics and yield consistent, reproducible results. 

Even when starter cultures are unnecessary, manufacturers may add starter cultures for guaranteed consistency from one batch to another, especially when selling products to expectant customers. 

Previous batch

Still, another technique called backslopping, is based on a similar premise as starter cultures. The only difference is that a portion (usually the brine) of a finished ferment is added into a new batch of food ingredients. This inoculates the new ferment with specific microbes to allow them to quick gain the competitive edge over other microbes. 

Some artisans making sauerkraut or kimchi backslop, though it’s often unnecessary given adequate salt, temperature, and a true anaerobic environment. 

Fermented foods with live vs. dead microbes

Another way to classify fermented food is based on microbial viabilty. While the process may involve live microbes for fermentation at one point or another, they may not be in the finished product due to heat or filtration.

Fermentation as a step in the process

In the case of coffee and cocoa, fermentation of the beans imparts unique aroma quality, colour change, and deep flavour. By the time the beans are finished processing and ready to sell, fermentation microbes are long gone due to drying and roasting. 

Sourdough bread is similar. Yeast leaven the dough by producing carbon dioxide. Lactic acid bacteria also convert some sugars in the flour into lactic acid, giving a sour taste. Then the final baking step inactivates these live microbes.

Other examples of fermented foods without fermentation microbes are beer and wine. Filtration or centrifugation remove the majority of yeast. 

By contrast, kombucha, kefir, yogurt, sauerkraut, kimchi, fermented pickles, and tempeh retain live microbes, provided these foods are not heat processed (i.e. canning) to extend the shelf life. 

Certainly, there are benefits to having live microbes in fermented foods at time of eating. 

However, the benefits of consuming fermented foods doesn’t end with viable microbes. Even fermented foods with dead microbes offer benefits such as:

• inhibiting microbes that make us sick (E. coli, Salmonella)
• creating new nutrients (B vitamins and vitamin K)
• deactivating anti-nutrients (phytic acid)
• making non-nutritive health compounds more bioavailable (antioxidants, anti-inflammatory compounds from plant-based foods)
• improving digestibility (bread, vegetables, and dairy products)
• enhancing flavour (umami flavours, aroma of coffee beans, olives) 

All of these benefits remain even after the removal or deactivation of microbes.

Fermentation food as the end product

In contrast, the advantage to eating fermented foods with live microbes is microbial action in the body. 

Let’s be clear: Most fermented foods do not have probiotics like you’d find in probiotic supplements or probiotic-added foods.

Microbes found in fermented foods may have similar actions to probiotics as recently discovered (3), but research is behind in identifying the exact strain and levels required to exert health benefits. It’s also hard to guarantee the same strains and levels from various manufacturers, batches, and locations.

Until research catches up, we can acknowledge that fermented foods with live microbes are doing something really good for health. Anyone who consumes these foods can testify to positive changes such as improved immunity, gut healing, and lower inflammation.

Moreover, many don’t need a research article to tell them how they feel from fermented foods. The evidence speaks for itself.

Final thoughts

Fundamental to fermenation are microbes, carbohydrates, and environmental conditions. Microbes use carbohydrates in grains, vegetables, fruit, legumes, and even meats as fuel. In return, they create flavourful, value-added end products, some of which retain live microbes from start to finish.