Fermented Foods


A Potted History of Fermentation

Imagine how excited our Anthropocene ancestors must have been when they discovered fermentation in action for the first time. Getting that warm fuzzy feeling from eating over-ripened fruit might have been where it all started. Recent investigations have identified what may have been the world’s first brewery, with 13,000-year-old residues of beer having been discovered in a cave near Haifa, Israel. The consumption of yoghurt may date back as far as 10,000 years, when the action of thermophilic bacteria in raw milk kept in goatskin bags produced a soured, thickened, creamy foodstuff, the heat of the African climate providing the perfect temperature for it to set. It must have been a revelation – a way of both preserving and extending the diet. Over subsequent years, sauerkraut, kimchi, kombucha, kefir and water kefir have all have had their moments of discovery.

Interestingly, these foods have endured for thousands of years, probably because they could be preserved for many months, and were also found to be beneficial to human health. It is even possible that these early diets influenced the formation of the human gut microbiota. Learn more about preserving wild foraged foods through fermentation and canning.

What is ‘fermentation’?

Pickled red onions in a sealable glass jar

The word ‘fermentation’ means different things to different people. To the microbiologist or biochemist, it is the utilization of carbohydrates by microbes in the absence of oxygen. To the wine or beer maker, it is the action of, specifically, yeast upon sugar to make alcohol. For someone who is interested in fermented foods, however, the definition becomes much wider; it is not restricted to precise biochemical pathways and can include any food that is pleasantly or usefully altered by microbes:

  • Fermentation is a controlled process where microbes use carbohydrates to produce a range of useful end products, including lactic acid, alcohol and acetic acid, which can also preserve and enhance food and make new flavours.

One of the most curious things about fermentation is how it differs from decomposition – the process by which food rots. Both are carried out by microbes, but the two outcomes are poles apart. Consider a cabbage that has been left sitting in the vegetable basket for some time; the leaves start to yellow, bacteria and fungi start to feed upon it and after three or four weeks it will be a pile of black-brown mush. However, by removing the oxygen and adding a little salt – that is to say, controlling the conditions in which it finds itself – it is possible to supress the growth of the microbes associated with decay, while encouraging others to produce lactic acid. The result will be a perfectly preserved, nutritiously enhanced vegetable, sitting in a delicious tangy brine.

Doing It Yourself

Changing the humble cabbage into sauerkraut (and, indeed, milk into yoghurt or tea into kombucha) involves science, alchemy and a little magic, but it is essentially a simple process. However, making your own kimchi, fermented chilli sauce or preserved lemons will introduce you to a whole new range of flavours that you never knew existed. And you will have created them all on your own – well, you and just a few billion microbes!

Of course, you could just pop to the shops for your kefir and sauerkraut, so what are the benefits of doing it yourself? First, when processes are industrialized, corners are cut, natural variation is eliminated, and products change. For example, many brands of shop kefir are made by reconstituting acid whey waste from commercial Greek yoghurt production with isolated milk proteins to make a base. Individual bacterial cultures are then added to the mix and a short fermentation conducted. This is a far cry from the kefiran-rich symbiosis of home-made milk kefir. Similarly, much commercially produced sauerkraut is pasteurized, so that it remains stable for transportation and storage. Often, starter cultures are introduced for reproducibility purposes, reducing the natural variety of strains involved.

Second, home fermentation is extremely economical. While artisanal fermented foods are comparatively expensive to purchase, because the processes are difficult to scale up, they are easy to do yourself in small quantities.

Fermentation can also be great as a collaborative experience – large-scale vegetable prep is best done with friends, with chatter and sharing of expertise and ideas. It is often better to be shown how to do something than to read about it, which is probably why fermentation workshops are so popular. Hopefully you will have the confidence to be one of the expertise sharers after using this book.

The Human Gut

There is a growing body of evidence around the health benefits of fermented foods, but why exactly are they good for human health, both prebiotic and probiotic? During fermentation, microbes synthesize vitamins and minerals, increase the digestibility of proteins and carbohydrates, increase the bioavailability of phytochemicals (plant compounds) and produce bio-active compounds that have important health benefits. Many of the microbes involved are probiotic, probably leading to the prevention and improvement of many chronic and metabolic conditions.

The Personalized Diet

As each person’s microbiota is as individual as that person, researchers have been studying the body’s individual responses to food. The ‘Predict’ study has looked at the responses of identical twins to the same foods. Even identical twins have different microbiota, and they do not have the same response to food; their glucose, insulin and dietary fat levels (which may be used as metabolic markers) were found to vary significantly after the consumption of the same foods.12 Another study has shown the same sort of results with people’s individual responses to bread.13 However, even with this knowledge, the next step – what to do with it, in order to give personalized dietary advice – is complicated. It is thought that only a fraction of the responses were due to the fat, sugar or protein content of the food. The rest was probably to do with the micronutrients, or even additives from ultra-processed food. Discover more about the science of canning.

How to Eat Fermented Foods

Glass jar of oil infused with dried chilies

Can fermented foods change your life? Possibly, especially if you have previously been a sickly person, seemingly susceptible to every passing germ. Although not everyone will see immediate benefits, as it depends on the status of their own particular gut, in preventive terms, the impact of fermented foods could be significant. There is a possibility that metabolic and autoimmune disorders or even cancers could be avoided by maintenance of good gut health, but a major retrospective cohort study will be required before this can be asserted.

Eat fermented foods little and often; they are nutrient-dense, and fermented vegetables have always been salted. Aim for diversity, with several different types on the go at the same time!

All fermented foods are extremely nutrient dense and the additive effects of too much of a good thing are unknown. Apart from purchased yoghurt cultures, it is not possible to know what probiotic microbes they contain or what microbes are in your own microbiota and how they might interact. As a result, it is necessary to start eating fermented foods in small quantities – a spoonful of sauerkraut, a couple of sips of kefir – and then see how you feel. Any gastrointestinal gurgling is likely to pass as the microbes are usually transient gut visitors. The amount can then be increased gradually over a few days. This is especially important if you have IBS/IBD, as individual responses can differ hugely.

Fermented foods are suitable for almost everyone, but there are caveats. You should start eating them when you are well, not when you are in the middle of any kind of serious illness, especially any form of cancer, or any other condition where you may be immuno-compromised. If you have had recent gastric, hepatic or dental surgery, you must check with your consultant first. Occasional infections have arisen post-surgery in chronically ill patients; almost all caused by large doses of just one type of microbe from probiotic capsules. In this regard, the natural symbiotic interactions of fermented foods may be preferable to capsule monocultures. Some researchers are concerned that antibiotic resistance genes present in the environment could transfer to probiotic bacteria. To be honest, they probably already have, and into lots of your gut microbes.

Fermented vegetables have a 2% salt content, so you should be aware of this if you need to watch your intake. All fermented foods also contain the biogenic amine histamine to varying degrees, which can cause allergic reactions in intolerant individuals. Remember, though, even if you cannot tolerate fermented foods, you can still improve your gut health through the prebiotics route: diet, fibre intake and exercise.

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