Why a hole is worth a second look
The holes in Swiss cheese are, strictly speaking, nothing at all. They are pockets of gas and empty space inside a wheel of Emmentaler, and yet they are the single feature that makes the cheese recognisable from across a room. Children draw them, cartoon mice burrow through them, and supermarket packaging relies on them to tell you what you are buying before you read a single word. It is a strange situation when the most famous part of a food is the part you cannot eat, and that strangeness is exactly why the holes are such a good place to go looking for ideas. They invite a question that creative people, engineers and scientists ask all the time in different words: what does the empty space tell us about the thing around it?
This post takes that question seriously and follows it in several directions. It starts with the microbiology of how the holes actually form, including a century-old puzzle that Swiss researchers finally cracked in 2015 with the help of CT scanners and a pinch of hay. It then looks at what happened when the holes started disappearing from modern cheese, at the famous safety model that uses cheese slices to explain why accidents happen, at a mathematician from Bern whose “Swiss cheese” was forgotten for years, and at the artists and designers who treat empty space as a material in its own right. Along the way, the recurring lesson is a simple one: a hole is never just an absence. Something made it, and it shapes everything that surrounds it.
The science of the eyes: gas, bacteria and a pinch of hay
Cheesemakers do not call them holes at all; they call them “eyes”, and a wheel that fails to develop them is described as “blind”. The eyes are the visible result of a quiet relay race between microbes. First, starter cultures turn the sugar in milk into lactic acid. Then a second organism, Propionibacterium freudenreichii, takes over during the warm ripening phase and breaks that lactic acid down into propionic acid, acetic acid and carbon dioxide. The two acids give Emmentaler its sweet, nutty flavour, while the carbon dioxide has nowhere to go. It dissolves into the young cheese until the curd is saturated, and then it gathers wherever it can find a weak spot, slowly inflating a bubble. According to the reference summary on cheese eyes, a large 80 kg wheel produces so much gas that only about 20 litres end up in the eyes, while roughly 60 litres stay dissolved in the cheese and around 40 litres escape altogether. The person who ripens the cheese, the affineur, can steer the size and shape of the eyes by adjusting the storage temperature, which is a reminder that even this “natural” feature is shaped by human judgement.
The gas, however, only explains half of the story, and for about a century that missing half was a genuine scientific puzzle. In 1917 the American dairy scientist William Clark published a detailed study, “On the Formation of ‘Eyes’ in Emmental Cheese”, which correctly identified bacterial carbon dioxide as the source of the holes. What Clark could not explain was why the gas gathered in some places and not in others. A bubble needs somewhere to begin, in the same way that a raindrop in a cloud needs a speck of dust to condense around, and nobody knew what those starting points were inside a wheel of cheese.
The answer came from Switzerland in May 2015. Researchers at Agroscope, the federal centre for agricultural research, worked with the materials scientists at Empa to watch cheese ripen from the inside. They used computed tomography, the same CT technology used in hospitals, to follow the number, size and position of the eyes over 130 days. In their trials they made experimental Emmentaler from microfiltered milk, which is almost completely free of particles, and then added tiny, carefully measured amounts of powdered hay, ranging from a fraction of a milligram to a few milligrams. The result was striking: the more hay they added, the more eyes formed, and the researchers found they could control the number of holes almost at will. Microscopic bits of plant material had been the missing seeds all along. They give the carbon dioxide a place to collect, and without them the gas simply stays dissolved. For anyone looking for a metaphor, it is hard to beat. The energy was always there in the form of gas; what was missing was a tiny, slightly messy point of contact that allowed that energy to take shape.
When the holes disappeared: the problem of milk that is too clean
The hay discovery did more than satisfy curiosity, because it explained a problem that Swiss cheesemakers had been worrying about for years. Older producers remembered winters when Emmentaler tended to have too many eyes, but in the 10 to 15 years before 2015 the opposite happened: wheels came out of the cellar with noticeably fewer and smaller holes, a trend German-speaking cheesemakers came to call Löcherschwund, or “hole shrinkage”. The cause turned out to be progress itself. Traditional milking in the barn, with milk collected in open buckets, had allowed tiny particles of hay dust to drift in naturally. Modern, closed milking systems pipe the milk directly through filters into sealed tanks, which is excellent for hygiene and food safety but leaves almost nothing behind for the carbon dioxide to gather around. In other words, the milk had become too clean to make the cheese look the way people expected it to look.
What followed is a wonderfully Swiss story about tradition, regulation and the meaning of authenticity. Emmentaler carries a protected designation of origin, known as AOP, and its production rules forbid most additives and processing aids. In 2022 the producers’ organisation Emmentaler Switzerland asked the Federal Office for Agriculture to allow small amounts of hay flower powder in the official specification, so that cheesemakers could reintroduce the particles that modern milking had removed. The federal office refused, arguing that the cheese was still of very high quality and worrying that the powder would let producers standardise their wheels in an industrial way. The producers appealed, and in April 2025 the Federal Administrative Court ruled in their favour. The judges stressed that relaxing the rules for a protected product must remain the exception, but they accepted the evidence and made a memorable observation: because a cheese can also end up with too many holes, adding hay powder does not guarantee a uniform, factory-perfect result. The full judgment, B-6947/2023, is available in German, and the federal office later decided not to appeal.
There is a lesson here that reaches far beyond the dairy. Many of the things we optimise away in the name of efficiency, cleanliness or control turn out to have been doing quiet, invisible work. An open-plan office without chance encounters, a writing process without wandering thoughts, or a product roadmap without room for experiments can all become a kind of microfiltered milk: pure, predictable and strangely flat. The Emmentaler solution is instructive because nobody suggested going back to dirty buckets. Instead, the cheesemakers deliberately reintroduced a small, measured amount of the old randomness. For creative work, that might mean scheduling an hour each week for reading outside your field, keeping a notebook of half-formed ideas, or inviting someone from a completely different discipline to review a project. You do not need chaos to get holes; you need just enough grit for something interesting to start forming.
The Swiss cheese model: how holes became a way to think about failure
Outside the kitchen, the most influential idea ever inspired by Swiss cheese probably belongs to the British psychologist James Reason, who spent much of his career at the University of Manchester studying why people and organisations make mistakes. In a 1990 paper for the Royal Society on latent human failures in complex systems and in his book Human Error, published the same year, he laid the groundwork for what became known as the Swiss cheese model of accident causation. The image is simple enough to sketch on a napkin. Picture an organisation’s defences against disaster as a row of cheese slices standing one behind the other: training, procedures, alarms, supervision, equipment checks and so on. Every slice has holes, because no defence is perfect. Most of the time a hazard passes through a hole in one slice and is stopped by the solid part of the next. A real accident happens only on the rare occasions when the holes in every slice happen to line up, opening a straight path from hazard to harm.
Reason explained the idea to a wide medical audience in a short and much-cited 2000 article in the BMJ, “Human error: models and management”. There he contrasted two ways of looking at mistakes. The “person approach” looks for the careless nurse or the distracted pilot and tries to fix the individual through blame, retraining or discipline. The “system approach” accepts that humans will always make errors and asks instead how the system allowed an ordinary slip to become a catastrophe. In his model the holes come from two sources: active failures, which are the unsafe acts of people at the sharp end, and latent conditions, which are weaknesses built into the system long before anything goes wrong, such as understaffing, confusing equipment design or unrealistic schedules. Crucially, the holes are not fixed. They open, close and drift as conditions change, which is why a system that looked safe yesterday can fail today. The model has since spread into aviation, healthcare, process engineering and computer security, where the same idea goes by the name of layered security or defence in depth. During the COVID-19 pandemic it found an entirely new audience: virologist Ian Mackay’s version of the diagram, with a slice for each everyday protective measure, went viral, and in New Zealand microbiologist Siouxsie Wiles and illustrator Toby Morris used it to explain the country’s layers of pandemic defence.
No metaphor is perfect, and safety researchers have pointed out the holes in this one too. A 2005 paper in BMC Health Services Research asked, with a nice pun, whether there are holes in the metaphor, noting that people use the model in inconsistent and sometimes vague ways, and a 2020 review in Safety Science traced both the good and bad reasons for its enormous popularity before concluding that it remains relevant. Still, the core insight is a generous and useful one, and Reason, who died in February 2025, left behind a way of thinking that applies to creative work as much as to operating theatres. Instead of trying to build one flawless wall, you stack several imperfect ones. A writer does not need a perfect first draft if there is also a second draft, an editor, a friend who reads it aloud and a night’s sleep before publishing. Each layer will miss things, but the holes are unlikely to line up. And when something does slip through, the most productive question is not “who failed?” but “which holes aligned, and how can I shift one of them?”
Holes in mathematics and the cosmos
If cheese holes can explain plane crashes, it should not be too surprising that they have also found their way into pure mathematics, and here the story returns to Bern. Alice Roth was born in the Swiss capital in 1905, studied mathematics, physics and astronomy at ETH Zurich and worked with the celebrated mathematician George Pólya. In 1938 she earned her doctorate at ETH, one of the very first women to do so in mathematics, with a thesis so highly regarded that it won the ETH silver medal. Hidden inside it was a clever construction that mathematicians now simply call the “Swiss cheese”. Imagine taking a solid disk and punching out an infinite sequence of ever smaller circular holes, chosen so that the holes are scattered densely everywhere while their total size stays finite. What remains is a lacy, almost ghostly set with no solid interior at all. Roth used it to show something surprising about approximation: on such a set, not every continuous function can be imitated arbitrarily well by simple rational functions. The holes, in other words, were not decoration. They were the reason the mathematics worked.
The rest of Roth’s story is a lesson in how good ideas can themselves disappear into a hole. A year after her thesis was published, the Second World War broke out, and her result was largely forgotten. Roth spent the next three decades teaching mathematics and physics at a private school in Bern, while in 1952 the Soviet mathematician Sergei Mergelyan independently rediscovered the same kind of example. It took until the late 1960s for her priority to be properly recognised. Remarkably, after retiring from teaching in 1971 she returned to research and produced new results, including what became known as Roth’s fusion lemma, which influenced a new generation of mathematicians. Since 2022 the Department of Mathematics at ETH has honoured her with the annual Alice Roth Lecture, given by outstanding women in mathematics. Her story is a reminder that an idea which seems to have vanished can be waiting, perfectly intact, for someone to look in the right place again.
Physics has its own Swiss cheese, and it operates on the largest scale imaginable. In 1945 Albert Einstein and his young assistant Ernst Straus asked a deceptively simple question: if the universe is expanding, why don’t individual stars and their planets drift apart along with it? Their answer, published in Reviews of Modern Physics as “The Influence of the Expansion of Space on the Gravitation Fields Surrounding the Individual Stars”, is now known as the Einstein–Straus vacuole or the Swiss-cheese model. They imagined a smooth, expanding universe and then cut spherical bubbles out of it, placing all the mass that had been removed from each bubble at its centre. Inside each hole, space behaves as if the cosmic expansion did not exist, while the bubble’s edge keeps moving outwards with the rest of the universe. Later cosmologists used this “Swiss-cheese universe” to study how lumps and voids in the cosmos bend and delay light on its way to us. The model has known weaknesses, since it relies on perfectly spherical holes and is unstable when they are distorted, but the picture it offers is still a lovely one: a universe full of quiet pockets that are shielded from the restless expansion all around them. Anyone who has tried to protect a few hours of deep work from an ever-growing calendar will recognise the appeal.
Negative space in art, design and nature
Artists have understood the power of holes for a long time, but one moment in 1931 stands out. The English sculptor Barbara Hepworth was working on a small abstract carving in pink alabaster when she decided to cut straight through it. The piece, Pierced Form, was later destroyed during the Second World War, but its effect on modern sculpture was lasting. Hepworth later recalled the experience in almost spiritual terms: “When I first pierced a shape, I thought it was a miracle.” By opening the stone, she let light and air become part of the work and invited the viewer to look through the sculpture rather than only at it. Her friend and rival Henry Moore soon took up the idea, and the Tate’s essay on Hepworth’s “hole of life” recounts how Moore even called 1932 “the year of the hole”. For both artists, the empty space was no longer what was left over after carving; it was a shape in its own right, as carefully considered as the stone around it.
Designers talk about the same idea under the name of negative space. The classic demonstration is the Rubin vase, popularised by the Danish psychologist Edgar Rubin, in which the same black-and-white image reads either as a vase or as two faces in profile, depending on whether your brain treats the empty area as background or as figure. Typographers spend surprising amounts of time on the enclosed spaces inside letters such as o, e and a, which are called counters; when those little holes are too small, text becomes hard to read at small sizes. Japanese aesthetics has a word, ma, for the meaningful gap or pause between things, whether in a garden, a room, a piece of music or a conversation. In every case the lesson is the same as in the cheese: the empty parts are not passive. They give the solid parts their shape, their rhythm and their legibility.
Nature, too, makes surprisingly deliberate holes. The popular houseplant Monstera deliciosa is widely known as the Swiss cheese plant because its mature leaves are full of slits and openings, a feature botanists call fenestration, from the Latin word for window. Young plants on the dark forest floor grow solid leaves, and the holes only appear once the plant climbs towards the light. In a 2013 paper in The American Naturalist, provocatively titled “How did the Swiss cheese plant get its holes?”, biologist Christopher Muir proposed an elegant explanation. In a rainforest, light reaches the understorey in brief, scattered sunflecks. A holey leaf uses the same amount of tissue to cover a much larger area, so it intercepts a slice of many more sunflecks, even if it misses part of each one. According to his model, the holes do not increase the average amount of light the plant receives so much as make its supply steadier and its growth less of a gamble. Other researchers have suggested that fenestration also helps rainwater reach the roots, and the question is not entirely settled. Either way, the Monstera offers a thought worth keeping: sometimes the smartest way to catch more opportunities is not to grow a bigger solid surface, but to spread out and leave gaps.
Practical ways to put “Swiss cheese thinking” to work
It is one thing to admire holes and another to use them. The stories above suggest a handful of habits that anyone can borrow, whether you write, design, build software, run a team or simply want to think more freshly about a problem.
- Look for your speck of hay. Ideas, like carbon dioxide in a young cheese, often float around in a dissolved state for a long time without taking shape. What turns them into something visible is usually a small, specific point of contact: an odd customer complaint, a strange detail in a dataset, a photograph that does not quite fit. When you notice a tiny irritant like that, write it down and treat it as a possible nucleus rather than as noise.
- Reintroduce a measured amount of randomness. The Emmentaler producers did not abandon hygienic milking; they added a precise pinch of hay back in. In the same spirit, you do not have to give up an efficient workflow to make room for serendipity. Reserve a fixed slot each week for reading outside your field, take a different route to work, or ask someone with an unrelated job to look at your draft.
- Stack imperfect layers instead of chasing one perfect wall. James Reason’s model is a reminder that every check has holes, including your own judgement. Rather than trying to make a single step flawless, add several independent ones, such as a checklist, a peer review and a cooling-off period, so that their weaknesses are unlikely to line up.
- Design the empty space on purpose. Hepworth’s pierced stones, the counters inside letters and the Japanese idea of ma all treat emptiness as a material. Apply that to your own work by deciding deliberately where the white space goes on a page, where the pauses fall in a presentation and which hours in your calendar stay unbooked.
- Spread out to catch more sunflecks. The Monstera’s holes let a leaf cover more ground with the same tissue. For creative work, that suggests a broad, loosely connected collection of interests and inputs rather than one dense, narrow focus, because breadth makes it more likely that a stray beam of inspiration will land somewhere useful.
- Revisit what fell into the gaps. Alice Roth’s Swiss cheese was forgotten for years before anyone noticed its value again. Old notebooks, abandoned drafts and half-finished side projects often contain ideas that were simply early. Schedule an occasional afternoon to go back through them with fresh eyes.
- Protect a quiet vacuole. Einstein and Straus described pockets of space that stay calm while everything around them expands. Most of us need something similar: a time, a place or a device-free routine that is shielded from the constant growth of messages, meetings and obligations, so that ideas have room to form.
Conclusion: the shape of nothing
The next time you cut a slice of Emmentaler, it is worth pausing for a moment before you eat it. Each of those eyes is the visible trace of an invisible process: bacteria quietly turning acid into gas, a speck of hay giving that gas a place to gather, and a cheesemaker deciding how warm the cellar should be and for how long. The same humble image has helped safety experts make hospitals and aircraft safer, given mathematicians a way to explore the limits of approximation, offered physicists a model of quiet pockets inside an expanding universe, and inspired artists to cut light into stone. What links all of these stories is a shift in attention from the solid to the empty, and from asking “what is there?” to asking “what made this gap, and what does it make possible?”
That shift is available to anyone. The holes in Swiss cheese show that absence is rarely random, that a little imperfection can be the seed of something beautiful, and that a system built from imperfect layers can be stronger than one that pretends to be flawless. They also show that it is possible to lose something valuable through too much tidiness, and that the cure is not chaos but a careful, deliberate pinch of the unexpected. Whether you are writing a novel, designing an app, planning a project or simply looking for a new idea on a grey afternoon, it might be worth asking where the holes are in your own work, and whether some of them are exactly where they need to be.