Microbe Cabinet Chronicle: Fermenting in Berlin

I. Forming the Microbe Cabinet

Eight years ago, I created an artwork with wild-fermented yoghurt as its theme, drying yoghurt starter onto cloth. I was never that fond of drinking yoghurt; back then, what really drew me in was seeing the possibility of wild fermentation as a form of artistic expression. So naturally, I never carried on with yoghurt fermentation as a daily habit or hobby.

Two years ago, my partner and I decided to move in together, and at last I could arrange the rooms just as I had always pictured them and set aside dedicated space for fermenting my own food. At the same time, having switched to freelancing, I no longer kept to a nine-to-five schedule; life suddenly surfaced again, and free time rushed at me from every direction. So I dove headfirst back into the world of microbes, cultivating my own fermented foods.

This time, fermentation was driven by appetite and drool — a purely appetitive pursuit. Entrusted with yeast by a friend, I started baking bread; to beat the summer heat, water kefir once again took up residence in my kitchen; and after returning from my hometown, I eagerly set about making pickles… And so jars and bottles drifted through the kitchen, in and out — some stationed themselves for good, while others lingered for just a season before making a hasty exit.

◉I turned a dead corner in my flat into a cabinet for room-temperature fermented foods, jokingly christening it my “Mikrobenkabinett”. In German, Kabinett can mean both a display room and a cabinet of government — perfectly suited to the image in my head of all my microbes convening together in one room for a grand assembly.

II. Permanent Members of the Microbe Cabinet

I have tried so many fermented foods — yoghurt, cheese, sauerkraut, sour soup, kombucha, water kefir, fruit vinegar and rice vinegar, sweet rice wine, bread, miso, rice bran pickles, tempeh, fruit-fermented sufu, fish sauce… The very act of listing them gave me quite a shock. Without even realising it, I had already attempted so much.

Once you recognise the presence of microorganisms — once you understand which microbial community takes the lead at each stage of different ferments (lactic acid bacteria, acetic acid bacteria, yeast, and various moulds) — and treat them like pets, giving them a suitable home, it becomes very hard to fail.

Lactic Acid Bacteria

◉My pickle mother brine, seen under the microscope.

Pickles, salted vegetables and yoghurt are all made through lactic acid bacteria fermentation, which converts the sugars in vegetables and the lactose in milk into lactic acid. However, the lactic acid bacteria strains in pickles can, on top of this homofermentation, also carry out heterofermentation, producing a mix of other by-products (such as acetic acid, formic acid, ethanol or carbon dioxide).

The lactic acid bacteria in pickles are anaerobes, salt-tolerant and acid-tolerant. In a sealed, air-excluded crock with enough salt, lactic acid bacteria quickly outcompete other microbes and become the dominant culture — the most undemanding resident in my fermentation cabinet.

In my hometown, a pickle crock is called a “fermentation crock”.

This year, when I visited home, I received a bottle of mother brine that a friend of my āijīě — a Hunan dialect honorific for an elderly woman, usually one’s grandmother — had been maintaining for over twenty years. The moment I got back to Germany, I poured it into my pickle crock, extending its lifespan by her two decades. The lactic acid bacteria, so accustomed to garlic, Chinese shallots, yard-long beans and daikon in Changsha, have learned to develop a taste for parsnips, fennel, kohlrabi and cherry radishes in Berlin. With their ever-more-varied diet, the crock grows more fragrant with each feeding and becomes easier to tend.

And that scoop of crock brine has become the thread binding me to my conversations with my grandmother — between the everyday checking in on each other, I cannot help but report on the crock’s condition. It feels as though I have been entrusted with a precious living thing, a bond of friendship, and a flavour.

◉On the left, the crock just after I started feeding it. On the right, the crock at my āijīě’s friend’s house, over twenty years old.

◉In mid-September this year, my friend led me to a food performance at Berlin’s museum complex. We lit a wood fire and baked bread, invited the audience to stomp sauerkraut with their feet, threaded fruit into necklaces, and served free food to nearly ten thousand people. For those ten great barrels of sauerkraut, I had spent a whole week cultivating ten litres of pickle brine using the old mother liquid from my crock. We poured it over shredded cabbage, and over-excited children stomped it all afternoon — and, improbably, the flavour turned out quite respectable.

◉Besides the most traditional fermentation crock (water-brined pickles), this year I have also started making bran pickles. But since I live in a wheat-growing region and cannot find rice bran, I use wheat bran to cultivate a bran bed instead, seasoned with lemon and pepper. The pickled apples and cherry tomatoes are genuinely delicious.

Yeast

Yeast can break down sugar into CO2 and alcohol, making it useful for brewing and for aerating dough in baking.

I cannot drink, and have little interest in brewing. But over the past few years, tending a sourdough starter and baking bread have become the one hobby that keeps me company day after day.

The yeast for my bread came from a friend. In the early 1990s, a senior member of his family opened an organic shop selling their own wild-yeast bread. The sourdough starter had passed through several generations of the family over more than thirty years before finally reaching his hands two years ago, carried by a visiting relative.

As his friend in Berlin started baking bread, he began sharing the starter among the bread-making community there. Entrusted with those 100g of liquid starter, I have tended it ever since with great reverence.

◉Before I knew it, bread photos on my phone had piled up endlessly.

Over these two years, while baking bread, I have kept sharing the starter with friends, and of course they carry on spreading it. The result is that when I visit someone’s home, a complete stranger will occasionally cry out: So you’re the yeast person!!

It feels as though, without quite noticing, I have founded a rather enormous organisation.

◉A year ago, while taking part in a friend’s amateur theatre group, I wove my daily tending of the dough into the show. The dough, hurled at the wall, became a mask. I kneaded it, spoke to it, and it answered back with a different expression for every gesture of care.

◉In Berlin, I stumbled upon a community of “bread obsessives”. They scoff at the singular bread aesthetic promoted on social media — strong gluten, dramatic open crumb — and organise annual sharing sessions themed around different grains, inviting researchers, millers and bakers to share their craft, explore flavours beyond common wheat, and champion diversity in grain cultivation.

Acetic Acid Bacteria

Acetic acid bacteria are aerobic: they convert alcohol into acetic acid. This is why people often say that wine and vinegar share the same root — first there is wine, and then there is vinegar.

Vinegar lays the groundwork for all sources of sourness, while also reflecting each region’s growing areas and culinary preferences. In the rice-growing south of China, rice vinegar is the norm; in the north, grain vinegar is made from sorghum and wheat bran. In Europe, fruit vinegars fill the shelves: wine vinegar brewed from wine, apple vinegar brewed from cider.

When I occasionally spot in-season produce on sale, lacto-fermentation and vinegar-making are the first ways I think of for preserving those flavours long-term.

◉On German streets in September, plums of every variety hang in heavy clusters, tree after tree. This year, led by a friend, I couldn’t resist picking a whole basketful to take home and turn into plum vinegar.

Moulds

◉Rhizopus mould in jiuniang (sweet fermented rice).

One hallmark of East Asian fermented foods is the use of pastes and sauces made from various moulds.

Different moulds have their own common names and commercial names; shuttling between my mother tongue and foreign languages, I often find myself hopelessly confused. I have taken to compiling a classification chart for myself, listing the Latin names of different strains, to help me get to know the various mould families and their respective strengths.

Different strains of the genus Rhizopus are the workhorse moulds behind tempeh-making, among which rice mould Rhizopus oryzae is also used in brewing; different species under the genus Mucor are commonly employed in making sufu.

Aspergillus oryzae is commonly called the “Japanese qu mould” or “white qu mould”, while Aspergillus sojae is known as the “soy sauce qu mould”, also called “rice qu mould”. What people refer to as “black qu mould” is Aspergillus niger, while “red qu mould” refers to different species under Monascus, an entirely separate genus.

When it comes to moulds, one cannot avoid mentioning qu. Qu refers to a starter culture: a grain substrate (such as rice, wheat, barley, peas or oats) inoculated with or naturally enriched in mould-dominated microorganisms (such as the Aspergillus, Rhizopus and Mucor mentioned above), which can then be used to produce a new round of fermented foods (such as alcoholic beverages, soy sauce, vinegar and douchi (fermented black beans)).

For example: a rice-flour substrate inoculated with Rhizopus and brewer’s yeast becomes small qu, from which rice wine and jiuniang can be made. A broad-bean substrate inoculated with Aspergillus oryzae becomes mouldy beans, used to make doubanjiang (fermented broad bean chilli paste). A glutinous-rice substrate inoculated with Monascus and Aspergillus niger becomes Wuyi red qu, used for brewing red yeast rice wine and rose vinegar. And the celebrated Japanese rice koji is simply rice inoculated with Aspergillus oryzae — a substrate that the Japanese and the contemporary culinary world have developed into an inexhaustible range of uses: soy sauce, shio koji, miso, and so on and so forth.

In my home fermentation experiments, mould-based fermentation is the only category in which I rely on a fermentation box and commercial starter cultures. Traditionally, people inoculated grain substrates by covering them with straw and leaves, capturing the microorganisms naturally present in the air and the soil. However, this approach to wild fermentation is intimately tied to the specific temperature and humidity of a particular place and season, making it very difficult to replicate in an urban setting with a completely different climate and microbial ecology. Using industrially purified single-strain cultures, where each step can be precisely quantified, does indeed lower the learning threshold for mould fermentation. This is probably also why Japanese rice koji has taken the world by storm.

◉Red qu mould (Monascus purpureus) is widely used for brewing and vinegar-making along the coasts of Guangdong, Fujian and Zhejiang. The pigment metabolites produced during fermentation bathe food in a vivid red. These regions, where Monascus has been cultivated for generations, are also precisely the points of departure for many early Chinese migrants. Red Terroir is a series of still-life works I created in 2025, drawing on fermented foods from Southeast Asia, Japan and Europe — regions where the migration paths of the Chinese diaspora have historically intertwined. The work invites viewers to reconsider the connections between the spread of moulds and the great waves of human migration.

Multi-Community Fermentation

Of course, many fermented foods arise from the combined action of different microorganisms. Kombucha and kefir, for instance, are fermented beverages that rely on a SCOBY (Symbiotic Colony of Bacteria and Yeast). Wild yeast starters also harbour lactic acid bacteria and some moulds, while naturally produced qu involves the participation of yeast and lactic acid bacteria.

◉Growing a SCOBY is part of the kombucha- and vinegar-making process: it is a “pellicle” — a film formed by active microorganisms at the interface between the liquid and the air.

◉A pellicle incubated in a face-mask-shaped vessel, said to have skin-beautifying properties.

III. I Tend the Microbes, and the Microbes Tend Me

I have noticed that over the past few years, fermented foods have gradually become more widespread and fashionable among the urban middle classes.

As both a follower and an observer of trends, I sometimes feel a quiet wistfulness. Guided as they are by consumer-oriented social media, when we first begin to explore a particular type of food, we seem all too prone to becoming absorbed in techniques and tools. Tea drinkers love collecting and displaying teaware; coffee enthusiasts design themselves one set of expensive, intricate stainless steel equipment after another. As for fermentation, it becomes a pursuit of that open crumb structure in bread-making, that fine fizz in kombucha — after all, these are the parts that most catch the eye in image-driven media.

Still, I quietly hope that the pursuit of diverse flavours will, in time, lead those with taste-related hobbies to learn about varieties, genetics, terroir — the agricultural and crop-related issues behind flavour. If the fermentation trend does not stop at surface-level aesthetic appeal but instead gives urban dwellers a little more awareness of the varieties and origins of their ingredients, that too would be a fine thing.

◉The WWW (We, Wheat, Weave) project collects the various wheats and grains I encounter in daily life and while travelling, and, with the support of local communities, weaves them using traditional basketry techniques into a “growing” sculpture.

For me, exploring fermented foods has reawakened my awareness of the turning of the seasons and made me treasure the particularities of each region all the more.

Making fermented foods has anchored the cycles of my life: tending the yeast and nurturing the bran bed go on day by day, refreshing kombucha week by week, while vinegar, miso and other sauces mature over months or even years… Within these rhythmic cycles, I have found a pace that suits me, letting the rhythm of my microbes and the rhythm of my life slowly fall into step.

◉The story of Leonardo da Vinci “drawing eggs” is widely known in Chinese primary and secondary education. This fictional anecdote about the Western master stresses that diligence trumps talent, and that the birth of art depends on day after day of repetitive foundational practice. Such monotonous, repetitive labour is not only evident in the basic training of art but is also deeply rooted in the invisible caring labour of everyday life — housework, cooking, caregiving — all forms of nurturing work deemed uncreative. Circle Practice stems from my daily bread-baking routine. In each repetition of the same recipe, every loaf leaves its own mark on the baking paper, “drawing” a different “circle” that reveals the evolution of form and the passage of time hidden within repetition.

In selecting ingredients and providing habitats for my microbes, I have gradually learned that fermentation should follow the seasons and suit the land: in winter, moulding sufu; in the first lunar month, brewing wine; during the dog days, making sauces and drying white chillies; in late summer, pickling vegetables in rice bran; and in spring and autumn, when fresh produce floods the market, providing an endless stream of inspiration and ingredients for lacto- and acetic-acid fermentation.

At the end of this summer, a friend in Hangzhou and I ran a synchronised fermentation experiment across two cities. In her thirty-plus-degree heat she fed her sourdough starter, which wilted and languished, yet her jiuniang came together effortlessly. In my twenty-three-degree flat, I tried to keep my brewing qu alive — it either turned rancid or dried to cracks — while the sourdough starter I was maintaining in a rushed, careless fashion grew vigorously, yielding some truly delicious loaves.

The seasonal character of fermentation has reawakened my sensitivity to the changing temperatures and the produce of each season; and these parallel experiments across different cities with a friend have deepened my appreciation for the qualities that distinguish one place from another. Meanwhile, discovering how similar fermentation techniques have evolved along different paths and aesthetics in different cultures is a pleasure unique to cross-cultural fermentation practice.

Foodthink Author

Xu Xijing

Designer, fermentation enthusiast and contemporary art practitioner. Born in Changsha, Hunan, she now lives and works in Berlin. Her current practice and research focus on grains and fermentation. Principal of Dǒu Fǒu; in 2025, she co-founded TÍHÚ (food design studio). Contact: info@xijingxu.com

All images in this article are provided by the author

Editor: Xiao Dan