Endive root tonic
This is part of our series on upcycling farm by-products.
Table of Contents
i. Little-known but widespread, with untapped gastronomic potential
The Belgian endive (aka Witloof chicory, Cichorium intybus var. foliosum) is a striking member of the chicory family, sought after for its bitter flavour and ghoulish pallor. It is usually grown in two stages. First, endive plants are grown outside from seed to develop large roots, before being harvested and having their leaves removed. When shoots begin to resprout, the roots are replanted, and the new shoots grown in total darkness.¹ This process of ‘forcing’ mellows the bitterness of the leaves (from unpalatably to pleasantly so) and results in their distinctive appearance—troglodytes of the salad world.
All cultivated forms of chicory are varieties of the same plant, Cichorium intybus. Wild chicory and cultivated varieties grown for their roots (var. sativum) have been used in parts of Europe as a coffee substitute for centuries—at times through choice, at others through desperation—and are still popular today in, for example, New Orleans.² Leaf chicories are mentioned in writing by Pliny the Elder in the first century AD, and were a favourite of medieval Italian monks, though many of the charismatic radicchio varieties that we recognise today were only developed in the early 20th Century, despite their apparent ‘aura of tradition’.³ The forcing technique that gives Belgian endives their distinctive appearance has a serendipitous origin story; the mythology goes that in the mid-1800s, Frans Bezier, head gardener at Brussels Botanical Gardens, supposedly accidentally buried some unknown roots and forgot about them, before discovering their transformation in the spring.⁴
About 300-400,000 tonnes of Belgian endive are grown each year in the EU. Yet the leafy head only makes up about 40% of the total mass of the plant, meaning ~600,000 tonnes of roots are produced each year as a by-product of this industry. These roots are typically used as animal feed or to produce compost. Whilst neither of these uses is terrible per se, the true potential of this by-product may yet be untapped.
ii. Culinary R&D: the transformative potential of fermentation
Developing this recipe began with a happy accident similar to Frans Bezier’s. Kim was originally investigating how to use fermentation to create a more flavourful coffee substitute from Belgian endive roots, applying those existing traditions for root chicory to a by-product of producing leaf chicory. He trialled various methods to ferment peeled and unpeeled endive root, including with koji spores, different yeasts used in beer and wine-making, and the simple spontaneously fermented method featured here. Each provided unique flavour profiles that warrant further exploration.
After fermenting shredded endive root in water for 72 hours, he tasted and smelled the resulting concoctions. The spontaneously fermented one was particularly promising. The flavour profile had transformed from ‘rooty’ and unpleasantly bitter to one with citrus and fruity aromas and a pleasant balance of bitter and sour tastes. It immediately reminded Kim of tonic water—so letting flavour lead the way, he decided to pivot and develop the fermented endive root in that direction instead.
While exploring the fermented endive root for a coffee substitute got put on the back burner, we still think there is a lot of potential there. We’ll share our findings when we return to it. For now, we’re quite excited about this tonic.⁵
If all the Belgian endive roots grown in the
EU each year were spontaneously fermented
into a tonic water-style beverage, there would
be enough to make nearly 35 servings of gin
and tonic per year for every adult of legal
drinking age in the EU!
iii. Recipe
(a) Spontaneously fermented base liquid
Ingredients
700g Water
300g Belgian endive root (washed, unpeeled)
Method
Blend or grate the endive root (we used a Robot-Coupe, but a food processor or hand grater would also work).
Cover with the water in an airlocked container and ferment at room temperature for 3 days.
Strain and keep the water.
Filter the water through a 1-micron filter to remove microbes from the final product.⁶ This ensures shelf stability and preserves the nutritional components.
You could choose not to filter it, however if you don’t the mixture will continue to ferment. This should yield 700g of liquid. You can get more liquid, and potentially more flavour, by squeezing the fermented endive root solids; however, we found when doing so the liquid remained cloudy no matter how much we filtered it.
This base liquid can now be frozen until ready for use.
(b) Tonic syrup
Ingredients
500g Water
166g Sugar
33g Citric acid
40g Lemon skin
46g Lemongrass
11g Kaffir lime leaf
10g Juniper
0.6g Salt
Method
Mix all the ingredients and keep in the fridge for 3 days. Mix once a day.
Strain.
This syrup can be kept in the fridge until ready for use.
(c) Spontaneously fermented endive root ‘tonic’
Ingredients
400g Spontaneously fermented base liquid (a)
100g Tonic syrup (b)
Method
Mix the base liquid (a) and the syrup (b).
Carbonate.⁷
Serve with gin and ice, or drink as is.
iv. The science
Alongside the R&D process, we also wanted to explore the microorganisms in the fermentation and their impact on taste and flavour. To investigate which microbial species had grown during the 72-hour fermentation, Caroline extracted, sequenced and analysed DNA from the root and liquid samples using a method called shotgun metagenomics. The microbial ecology of each sample is shown in Figure 1.
Confirming our sensory impressions, Caroline found that the endive root had mostly undergone lactic acid fermentation, with its microbial ecology largely consisting of members of Lactic Acid Bateria (LAB), from the family Lactobacillaceae. This is similar to the microbial ecologies of kimchi and sauerkraut, both of which are also made of spontaneously fermented vegetables. The root tonic was shown to be very microbially active, comparable to livelier examples of the aforementioned LAB ferments.
Caroline also identified a high relative abundance of Gammaproteobacteria species, mainly Rahnella aquatilis. This species is a nitrogen-fixing enteric bacterium that is also associated with living root microbiomes, and has even been detected in kimchi. This points to a tantalising finding: that some microbes might be important for bodily, soil, and fermentation ecologies, perhaps even flowing between them.
Caroline completed this analysis on both the fermented root solids and the liquid, once using roots harvested in March and refrigerated for a month and again using roots freshly harvested in April. We found some interesting differences between the two batches.
The sample made from roots collected in March was sweeter and more acidic, likely because the sample was refrigerated for a month encouraging the conversion of starches into sugars, which subsequently provided more food for the LAB. This sample had a much higher presence of LAB, especially Leuconostoc mesenteroides and Leuconostoc miyukkimchii, and a much lower relative presence of Gammaproteobacteria.
The endive plants harvested in April had begun converting stored sugars into starches for new leaf growth. The lower sugar content and higher temperatures potentially disfavoured the growth of LAB, which in turn increased pH and enabled a greater presence of Gammaproteobacteria.
These findings highlight how variances in environmental conditions, geography, and agricultural practices can impact the end product, resulting in unique products through space and time. If a more consistent final product is desired, this could be achieved by using selected starter cultures assembled from the strains isolated from the wild fermentations. For now though we have been happy with the results from the wild fermentation, and enjoy noticing the slight variations from batch to batch and season to season.
Fermented endive roots may also be prebiotic and/or probiotic. They are rich in inulin (an important dietary fibre, also found in jerusalem artichokes) that promotes the growth of beneficial microbiota in the gut such as LAB, which may help to explain the emergence of lactic fermentation from the endive root. Belgian endive root also contains sesquiterpene lactones, which have many promising health benefits including possible anti-cancer properties.⁸
Caroline isolated strains of the species we identified, which can be used in future to investigate how these microorganisms interact, their impacts on flavour, and their potential probiotic functions.
Figure 1: The relative abundance of microbial compositions of fermented endive roots.
v. Why endive root tonic?
Tonic alone won’t save the world of course, however delicious it is. But it can certainly contribute to a better world. First, it’s a fun demonstration of the power of fermentation to valorise a by-product otherwise destined for compost or animal feed, upcycling it to higher-value use. Tonic water also typically contains quinine as a bittering agent, which historically is extracted from the bark of the endangered Cinchona tree endemic to South America. Nowadays pure synthetic quinine is also used to make tonic, since the discovery of its synthesis in 1944, though Cinchona bark is still sometimes used as a bittering agent for tonic and other alcoholic beverages. But using an undervalued agricultural by-product that’s right under our noses, rather than an endangered tree from South America or a pure compound produced through high-tech privatised corporate knowledge, could be the best option of all.
vi. For further exploration
Here are some questions we think could be worth exploring further:
What is the pre/probiotic potential of products made with fermented Belgian endive root?
What is the role of Rahnella strains in the fermented food environment?
Can we reconstruct the microbial ecology of the fermented endive root using isolated strains to better understand how the communities that are present impact flavour?
What steps could be taken to create a more standardised fermented beverage, if desired?
How does the drying of the roots for preservation once fermented impact the naturally present microorganisms?
How might different varieties of Belgian endives, different production methods, and even other members of the chicory family like the many varieties of radicchio, change the microbial communities and the resulting flavour profile of products made from their roots?
If you are interested in exploring any of these questions with us, feel free to reach out. We’d also love to know if you make it and what you think, and if you try it with another kind of chicory root or other bitter root tag us on Instagram at @sussyfig.
Read the paper here
Kim Wejendorp, Josh Evans and Caroline Kothe (2023). ‘Creating a spontaneously fermented ‘tonic water’ using Belgian endive root’. International Journal of Gastronomy and Food Science.
Contributions & acknowledgements
Eliot wrote the article, with contributions and editorial feedback from Josh. Kim, Caroline and Josh performed the original research that it is based upon.
Thank you to Mar van der List, farmer at Svanholm Gods, Skibby, Denmark, who provided the Belgian endive roots for this study. Shoutout to Christer Bredgaard, owner of Il Buco and La Banchina in Copenhagen, who has produced this recipe for use at his restaurants.
Kim photographed the Belgian endives growing at Svanholm Gods. Eliot photographed the tonic in our food lab. The graphics are from our publication.
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Endnotes
[1] Traditionally this would be done in the field, covering roots with metal plates to prevent light from reaching them (this traditional method is known as ‘grondwitloof’ in Belgium). At more commercial scales, roots are replanted indoors in a nutrient-rich medium in chilled warehouses - a more efficient factory-like practice known as ‘hydrowitloof’ that is controversial amongst more traditional growers. ‘Brussels Grondwitloof’ refers to endives grown outside in soil within a specific region of Beglium using heritage seeds and is a European Protected Geographical Indication (PGI); ‘Brabants Grondwitloof’ refers to endives grown outside in other parts of Belgium using hybrid seeds. per Brendán Kearney (2020), ‘The Bitter Fight to Save Belgian Endive from Extinction: Is the Weird and Wonderful “Witloof” Set to Disappear Forever?’, Belgian Smaak.
[2] Taylor Tobin (2023), ‘What is chicory coffee’, Southern Living.
[3] Margarett Waterbury (2023), ‘A history of radicchio’, Whetstone.
[4] Brendán Kearney (2020), ‘The Bitter Fight to Save Belgian Endive from Extinction: Is the Weird and Wonderful “Witloof” Set to Disappear Forever?’, Belgian Smaak. Note that the forcing technique isn’t actually unique to Belgian endives—a similar practice, called imbianchimento is also used to force other radicchios to similar effect in Italy, per Ibid.
[5] 400,000 tonnes Belgian endive produced in EU annually = 600,000 tonnes root (the root is 60% by mass of whole plant). During fermentation, the mixture = 30% root, 70% liquid by mass. After straining, there is 100% yield of liquid, therefore 600,000 tonnes of root would yield (600,000*7/3) = 1,400,000 tonnes or 1,400,000,000 kg of fermented liquid. If 150 ml tonic is used in a 200 ml G&T, and 150 ml of tonic contains 120 ml fermented liquid, then 1,400,000,000 kg divided by 0.12kg = 11.67 billion G&Ts could be made from endive root tonic. With 334.5 million people in the EU of legal drinking age (assumed above 18 years old, though this varies by country, and of course not everyone consumes alcohol), 11.67 billion divided by 334.5 million = 34.88 servings per person 11.67 billion/334.5million = 34.88 servings per EU adult of legal drinking age.
[6] For filtering equipment, we used a pressure container with a manual pump and a plate filter typically used for filtering beer or wine, passed through coarse filter pads first and then with a fine filter.
[7] We used a DrinkMate, which in our opinion is the best drinks carbonator on the market. It can carbonate any liquid, has a handy pressure-release lid to prevent explosions, and can also use standard CO₂ gas cartridges.
[8] Martin Chadwick et al (2013), ‘Sesquiterpenoids Lactones: Benefits to Plants and People’, International Journal of Molecular Science.