Fermenting Herbs

Guest written with Erin Evis from Apothecare Natural Health 

Fermentation: An easy and cost-effective way of enhancing bioavailability of medicinal herbs, and increasing the therapeutic value of fermented foods

 Whilst it has been around for millennia as a method of preserving foodstuffs, the ancient art of fermentation has undergone something of a revival in recent years. Once an old, fusty kind of technique oft associated with our depression-era grandparents or 60s-era hippies (think the so-called Manchurian Mushroom, or kombucha, that was popularly brewed on kitchen benches), fermentation has become a staple darling of many a fashionable instagram food and health influencer, with recipes and techniques abounding online.

Its connection to herbal medicine, however, is more tangential and not so well-known; despite this, it is worth exploring the benefits of this processing technique and its impacts on herbal products, particularly in relation to foods and culinary herbs, as a growing body of evidence suggests significant advantages in terms of nutrition and phytochemistry. 


What is fermentation?


Whilst there are a number of definitions for variations on the process, generally speaking, fermentation is the metabolic process of breaking down molecules, typically carbohydrates - sugars - into alcohol and/or acids, by way of the enzymatic actions of controlled microbial processes from bacteria and yeasts. Fermentation may take place either aerobically or anaerobically, depending on the product being created and microbes involved. Carbon dioxide is often released in the process. A simpler definition could be: foods or beverages produced through controlled microbial growth, and the conversion of food components through enzymatic action1.

Ferments may be wild, utilising bacteria and yeasts naturally present in the environment and in which fermentation tends to occur spontaneously, or controlled, using specific microbes and temperatures to deliberately innoculate the substrate and initiate the fermentation process - generally a starter culture. Common forms of fermentation involve dairy products (such as kefir, cheese, yoghurt), vegetables (such as kimchi, tempeh or sauerkraut), and herbal products (such as kombucha)1.

History of fermentation

 Fermentation has been utilised for millennia for the safe preservation of foods, with evidence of fermentation going back as far as 8,000BC. Every culture and every continent has a history of fermenting foods to help store them safely and prolong shelf life, meaning guaranteed food sources throughout long, harsh winters and poor growing seasons2. This was especially vital in ancient times, where stores of foods were essential for survival - fermentation was a form of insurance against famine and starvation, and ensured a glut of food was able to be utilised to its greatest extent.

Fermented foods and the great microbiome extinction

Because fermentation is essentially the result of the metabolic processes of these microbes and their growth and reproduction, the end product is one that is rich in microbes themselves. This has played a crucial role in creating the diversity of our microbiomes throughout history, adding plentiful beneficial bacteria to our diets and, thus, to our guts. However, as industrialisation has taken place and with it, the introduction of modern food preservation techniques that don’t require fermentation, plus a lack of diverse carbohydrates accessible to our microbiota (prebiotics), a mass extinction of many of these species has occurred in our guts, away from our eyes and without our even realising it3


The onset of and popularisation of appliances such as refrigerators, industrial canning, and mass production of processed and refined foods3, including those laden with artificial preservative compounds, has meant we no longer rely on fermentation as an essential technique for the safe preservation and storage of foods - the result is a diet that is largely void of these beneficial microbes, and a severe dearth of microbial diversity compared to that which our ancestors would have enjoyed.

Conversely, research has now proven that increasing quantities of fermented foods in the diet can increase the diversity of our gut microbiomes, meaning we have an effective means to address the imbalance and support our gastrointestinal health. This in turn may reduce inflammation and lower the risk of a number of chronic illnesses, as probiotics modulate and support the health of the gut and immune system4, 5.

Fermentation of herbs - increasing bioavailability of nutrients


In turn, for people working with medicinal herbs, one of the greatest - and most under-recognised - benefits of fermentation is that it is increasingly demonstrated to increase the bioavailability of nutrients and other phytochemicals. This includes those found in herbs, as the compounds the plant use to inhibit their breakdown are themselves broken down and thus the nutrients may be unlocked. This is of particular interest to anybody working with herbs as either food or medicine - or both - as the inclusion of culinary herbs within fermented foods can significantly bolster both the nutritional content of the end product, but also allow for some therapeutic effect to be imparted and the benefits of the food to be increased further6.

There has been a significant surge in research in recent years investigating the impact of fermentation on various medicinal herbs, showing not only increases in certain compounds - particularly polyphenols - across a number of species, but also the formation of new chemicals within the plants themselves after undergoing fermentation6, and changes to their microbiomes, also. Similarly, the bioavailability of other herbs and their therapeutic effects have been shown to be improved through fermentation with specific cultures, including the Chinese herb Danshen, and ginseng. 

In one study7, researchers examined the impact of fermentation with probiotic species Lactobacillus plantarum on bioavailability and digestibility of Basil (Ocimum basilicum) and Peppermint (Mentha x piperita). This in vitro study examined levels of phenolic compounds and flavanoids in the dried and fermented preparation versus the fresh plants, and found significant differences in the levels of antioxidant activity and bioavailability between the groups, with the fermented product being superior to the fresh herbs.

In another study8, looking at the impact of the natural microbiomes of two different Asteraceae species (Matricaria chamomilla and Calendula officinalis), we see emerging thoughts on the impact of fermentation on the microbiomes of the herbs themselves. In this study, the endo- and exospheres of the plants were examined both before and after fermentation. Each herb was found to have distinct microbial populations present naturally on the leaves, particular to the herb and also relative to the environment in which they’re grown, and significant shifts in these occurred during the six-week fermentation process. The authors speculate that this is likely a parallel benefit of fermented medicinal plants that occurs alongside their beneficial phytochemical profiles, and one that could further enhance their therapeutic effects. 


Practical implications for herbal medicine and functional foods

As we are all aware, many herbs used for culinary purposes have significant crossover in terms of their therapeutic benefits. For example, many of the Lamiaceae family herbs commonly used for culinary purposes in foods - including Thyme (Thymus vulgaris), Rosemary (Rosmarinus officinalis), Sage (Salvia officinalis), Lemonbalm (Melissa officinalis), Lavender (Lavandula officinalis), Mint (Mentha piperita), Oregano (Oreganum officinale), and Basil (Ocimum basilicum) - are also potent inhibitors of food-borne pathogenic microbes, possessing antimicrobial properties, and can help to preserve the foods themselves. The herbs of this family are known for their anti-inflammatory properties, and virtually all will support digestive processes and enhance the digestion of food9.

Likewise, medicinal members of other plant families have many millennia of use in culinary as well as therapeutic settings. Turmeric (Curcuma longa), Ginger (Zingiber officinale), Chilli (Capsicum anuum), Parsley (Petroselinum crispum), Coriander (Coriandrum sativum) are just some examples of many used traditionally in fermented foods around the world. Again, these all lend themselves nicely to the flavours of various fermented products easily incorporated into the modern diet, and able to cater to the modern palate. 


Although research is relatively scant for many of these herbs in terms of fermentation and enhancement of bioavailability, it is logical to extrapolate from the research that has been done into some of these herbs, alongside their traditional use in fermented products, that the fermentation process is likely to enhance the bioavailability of not only their macronutrients, but also many of their phytochemicals. For example, ginger is rich in phenolic compounds to which many of its therapeutic properties are attributed, including but not limited to gingerols, paradols, zingerols and others10. Given we’ve seen research indicating enhanced quantities of phenolics after fermentation of other herbs7, there is the strong potential for this to also account for some of the traditional therapeutic benefits attributed to ginger beer. 


Ginger, chilli and other pungent spices are commonly added to kimchi to enhance the flavour profile. Sauerkraut with parsley, juniper berry, caraway seeds, coriander, turmeric, ginger, and oregano are popular and common in both traditional and modern recipes. Herbal teas can be fermented to create probiotic health tonics. The enduring popularity of ginger beer is testament to its flavour as well as ease of use10, and the surging popularity of kombucha, and its ubiquity in fridges in cafes, restaurants and supermarkets - albeit of varying therapeutic benefit - demonstrates the increased awareness of fermented beverages and foods in the 21st century. 


To conclude, fermentation is an easily-utilised, cost-effective, but often undervalued means of enhancing the therapeutic properties of many of our most popular medicinal herbs, particularly those with a culinary crossover. While more research is needed to draw definite conclusions,  it is likely the incorporation of herbs into fermented food products, and thus into our diets, may help enhance the bioavailability and therapeutic properties of these herbs, reduce levels of anti-nutrients11, and will almost certainly be of benefit in terms of reduction in inflammation, improvement of the diversity of the microbiome, and supporting digestion, immune health, and overall wellbeing.

  1. Dimidi E, Cox SR, Rossi M, Whelan K.. Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease (nih.gov). 2019 Aug; 11(8): 1806.
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  8. Köberl M, Erschen S, Etemadi M, White RAW, El-Arabi TF, Berg G.  Deciphering the microbiome shift during fermentation of medicinal plants. 2019. Scientific Reports volume  9, Article number: 13461
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