sourdough loaf close up on dark background

Fermented Foods - What Are They And Why Should I Eat Them?

Dietitian and foodie Marnie Nitschke takes us on a deep dive into all things fermenting, from the science, right through to easy suggestions for incorporating fermented foods into your diet.

What are fermented foods?

To a lot of us, the idea of letting foods ferment and then eating them might not sound very appetising.  But stay with me here.  Humans have been using this technique for thousands of years to preserve the lifespan and enhance the flavour and texture of food.  Truth be told, you’ve likely eaten many different fermented foods or drinks this week without even thinking about it.  Common examples include yoghurt, cheese, sourdough bread, soy sauce, olives, beer and wine.

sourdough load close up with a bread knife

How are fermented foods made?

From a scientific perspective, fermented foods are produced through controlled microbial growth, a natural process that activates enzymes and converts the food into new ingredients. Mostly, this happens in an anaerobic (oxygen free) and often salty environment.

  • Wild ferments rely on naturally occurring yeast or bacteria present in the raw food or processing environment.  Examples of this are sauerkraut, kimchi and table olives, which are simply bottled with salt and then left to ferment.
  • Culture dependent ferments require the food to be inoculated with a specifically chosen live culture, to start the ferment.  This can be achieved with the delightful-sounding technique of ‘backslopping’ – where a small amount of a previously fermented batch is used as a starter culture (eg. in the sourdough bread process).  Alternatively, a specifically isolated and grown organism is added (eg. lactobacillus bacteria which ferment milk into yoghurt).

These days there are literally thousands of different varieties of fermented foods produced and enjoyed by various cultures around the globe.  Most can be  broadly categorised as lactic acid, fungal or alkaline ferments.


Lactic acid fermentation

Lactobacillus species tend to produce ferments with lower pH (higher acidity), and provide the characteristic sharp, sour and tart flavours we know and love in foods like yoghurt, cheese, sauerkraut, sourdough, kimchi and salami.

kimchi close up on  a dark bowl

Fungal fermentation

Utilises mould or yeast as a fermenting agent.  A delicious example of this is the versatile flavour bomb -  soy sauce - made from ground soy beans, wheat and salt fermented with koji (Aspergillus mould).

Alkaline fermentation

This type of fermentation produces less acidic compounds and a more complex, savoury, umami final product.  An example is natto – a Japanese whole soy bean condiment with a distinct (and rather divisive) taste and gloopy texture.

And here’s where it gets complicated!  Some fermented foods use a mixture of these methods, for example in kombucha brewing, where a SCOBY (Symbiotic Culture Of Bacteria and Yeast) is added to sweetened tea, and used to ferment it into to the tart, lightly carbonated beverage we see popping up on supermarket shelves everywhere these days. 

What are the benefits of fermented foods?
1. Extended shelf life or preservation

To keep it simple, fermentation produces a variety of end products, that can include carbon dioxide, ethanol (alcohol), organic acids and other molecules.  These effectively act as natural preservatives – making the food a hostile environment for less friendly organisms that would cause spoilage and illness.

2. Increased potential of nutrients to be absorbed and digested

The same compounds that preserve and enhance flavour can also substantially change the food matrix of the fermented product –

converting nutrients to more metabolically active molecules, and increasing their potential to be absorbed and digested. Here are just some examples:
    • The fermentation of soy beans results in lower levels of phytates (so called anti-nutrients that can block absorption of other nutrients) in the final product.
    • The sourdough bread-making process reduces windy oligosaccharides present in wheat, reducing digestive symptoms like gas, pain and bloating. The acidity of sourdough bread also makes it a lower Glycaemic Index option, which has a more favourable effect on blood sugar levels.
    • Fermented dairy products like yoghurt will contain more B vitamins, healthy organic acids, peptides and fatty acids, and less lactose (a sugar many people find difficult to digest) than milk. Most people who are lactose intolerant will tolerate proper Greek yoghurt quite well, in moderate amounts.
    • And let’s not forget about table olives! When first picked they are inedible, but fermentation (with the naturally occurring lactic acid and yeasts present on skins), allows enzymes to remove the bitter oleuropein, and render them a delicious option for your snack plate, salad or pizza.

    close up of green pickled olives in a bowl

    3. Prebiotic and Probiotic benefits

    Fermented foods can also provide both prebiotic and probiotic benefits to us, through their influence on the gut environment, and this can have flow on effects to chronic disease risk, immunity and even mental health.

    • Fermented foods can contain live and beneficial strains of microbes, and eating them regularly can increase the all-important diversity of our gut microbiome – that’s a no-brainer.
    • Let’s be clear here though – not all live microbes in fermented foods meet the criteria of being probiotics. To be considered probiotic, microbes will need to survive the acidic stomach environment, reach the large intestine alive and provide beneficial health effects to the host while they are inside us.
    • Because of the wide variability in the microbial profile of different fermented foods (depending on brewing conditions like temperature, time, and cultures used), making blanket statements or recommendations about fermented foods is really not good science. At the end of the day, no-one really knows exactly what bugs are living in your home brewed kombucha, or the salami hanging in uncle Nico’s shed.
    homemade salami slices with a cornichon
    • Another important point here is that not all fermented foods contain live microbes! Sourdough bacteria are killed by the high temperatures of baking, and that jar of pickles on the supermarket shelf has likely been pasteurised.  Look to the fridge for high quality products with live and active strains, if you’re after a potentially probiotic effect.

    And after the mini TED talk on the science of fermenting, if you’re feeling enthused, let’s talk practicality and food ideas.

    Here are just a few ideas for fermented foods you can start incorporating into meals and snacks.  Take note, however, that your gut may need a little time to adjust.   Fermented foods can be strong in flavour and acidic compounds, and won’t always suit the more sensitive gut straight off the bat.  Aim to slowly incorporate them over time, for the best results to your digestion and gut health.


    Kefir is usually made from milk fermented with ‘kefir grains’ (a symbiotic culture of yeasts and lactic acid bacteria) to produce a thick, sour, yoghurt-like and somewhat fizzy drink.  It’s a fantastic source of easily absorbable dairy nutrients which also has the potential to improve your gut environment over time. Most people drink kefir straight, but you can start out slow by adding small amounts to your cereal or smoothie, or using in salad dressings or baking while you’re getting used to it.


    Native to Indonesian cuisine, Tempeh is a fermented product of boiled and dehulled soybeans inoculated with a fungus (Rhizopus oligoporus). It’s kind of like firm tofu, but more soft, chewy and flavoursome (in a mushroomy way), and you can add it to curries, stir fries, noodle dishes and soups as a nutrient rich vegetarian protein.

    BBQ tempeh cubes on skewers with satay sauce

    Fish sauce

    A pungent, umani flavoured sauce featured often in Vietnamese and Thai cuisine, that will give a great depth of flavour to curries, fried rice and noodle salads.  Pairs well with lime.


    A traditional spicy Korean condiment made from fermented cabbage, ginger, garlic and spices. Use it as a condiment with stir fried or grilled meat or even throw it in a toasted cheese sandwich for a toastie with a twist (trust me – it works).

    Pickled vegetables

    I’m not just talking dill pickles in cheese burgers here. Experiment with pickled onions, beetroot and zucchini pickles on your cheese board, sandwich, wrap or with your roast.

    close up of pickled mixed vegetables in a lidded jar
    Sourdough bread

    It’s chewier, tastier and better for blood sugar levels than regular bread.  These days there are plenty of good sourdough options available at your local supermarket, and you might even find sourdough croissants and pizza bases if you look hard enough.


    Dosa is a popular South Indian crepe made from a fermented rice and lentil batter, and if you haven’t tried it yet you should!  Go online and find out where your local dosa restaurants are, or if you’re up for the challenge, try making dosa yourself and serving with dahl.

    close up of dosa on a white plate with a small bowl of chickpeas


    Buy it from the supermarket, get some from a friend, or if you’re adventurous, source a SCOBY and brew it yourself.  The best kombucha is tart (without being vinegary), a little fizzy and not overly sweet.  It’s a great no (or low) alcohol alternative to wine or beer, and a lot lower in sugar than soft drinks or fruit juice.


    Miso is a fabulous, umami flavour you may recognise from Japanese miso soup. Made from fermented soy beans and grains, it comes in a paste (similar to peanut butter in texture), and ranges from mildly sweet to quite salty.  Use in salad dressings, marinades, glazes and soups (head on over and try miso in the crispy tofu and soba noodle recipe).

    Here's a bit about Marnie ...