What Does Surströmming Smell Like? Sourced Facts

Most of the internet spells it surstromming, because most keyboards have no ö, and most of the internet is asking the same two questions: how bad, and why. Wikipedia answers the first with a sentence that has clearly been read aloud to a colleague. This report has the sourced version of both, the chemistry, a court case that ended with a can being opened in front of a judge, and a generator for the awkward note you will need to leave for the neighbors.

The short answer

Four things at once, on purpose. Wikipedia names the notes as pungent (propionic acid), rotten-egg (hydrogen sulfide), rancid-butter (butyric acid) and vinegary (acetic acid), and says surströmming has “one of the most putrid food smells in the world,” stronger than the fermented fish dishes hongeo-hoe, kusaya and hákarl. It is fermented, not rotten: the salt is there to keep the herring from rotting while it ferments.

Interactive, three choices

The Neighbor Notice 🥫

Draft the notice to residents for opening a can of surströmming. The building will tell you how much of its patience you used.

The traditional premiere is the third Thursday of August.

1. Where does the can get opened

2. How many cans

3. How much warning

Cologne tolerance used

Well inside

NOTICE TO ALL RESIDENTS

Re: Scheduled opening of one (1) can of fermented Baltic herring

On the third Thursday of August, the undersigned will open the above in the garden, punctured while immersed in a bucket of water. The date is the traditional surströmming premiere.

Wikipedia says this is how the can is often punctured, so that the escaping gas does not spray brine. The undersigned considers it the minimum.

A single can, for personal use.

This notice is posted seven days ahead. The undersigned would like credit for the lead time.

Residents are asked to close their windows. Complaints may be addressed to the can.

Tolerance used: 5%. Well inside. Comfortably within what a fellow tenant can be expected to tolerate. Expect a polite nod and a closed window.

Signed, the undersigned (a tenant in good standing, pending the above)

Share my notice

Tolerance used is a joke scale: every place, can count and lead time carries a number we picked, and no court has ever measured a neighbor in percent. The facts in the notice come from Wikipedia's Surströmming article. This is a humor page, not advice about how to treat your neighbors or your landlord.

The smell, in four notes

The Chemical process section of Wikipedia's article lists what the fermentation produces: propionic acid, butyric acid and acetic acid, plus hydrogen sulfide. The Production section pairs each with a smell. Fermentation also produces carbon dioxide, which is not a smell and is the reason for the next section.

Propionic acid

Pungent

That is the whole description Wikipedia gives it. Pungent is the word you use when a lawyer has approved the sentence.

Hydrogen sulfide

Rotten egg

The same gas is entry #6 on the Smell Index and a trace guest in the fart report. In a can it is one of four notes.

The fart report →

Butyric acid

Rancid butter

Entry #10 on the Smell Index, and the one that turns up in Parmesan, vomit and body odor. Surströmming is a greatest hits compilation, sold sealed.

Butyric acid on the Smell Index →

Acetic acid

Vinegary

The note you already own. It is in your kitchen cupboard, and nobody has ever been evicted over a salad dressing.

Fermented, not rotten, and the can bulges

Wikipedia says that during production just enough salt is used to prevent the raw herring from rotting while allowing it to ferment, for at least six months. Fermentation starts from a lactic acid enzyme in the spine of the fish, through autolysis. The salt raises the osmotic pressure of the brine above the zone where the bacteria responsible for rotting can thrive, and instead Halanaerobium bacteria such as H. praevalens decompose the fish glycogen into organic acids, which makes it sour.

Then the fish goes into the can, and keeps going. Wikipedia says fermentation continues in the can, causing it to bulge noticeably, “which would usually be a sign of botulism or other food poisoning concern in non-fermented canned foods.” A swollen can of surströmming is the product working as designed. A swollen can of anything else in your pantry is, per the same sentence, usually a warning sign, so do not take this paragraph into the kitchen.

From the Baltic to the bucket

SpringHerring are caught when they are in prime condition and about to spawn, before they have fattened.
About 20 hoursIn a strong brine that draws out the blood.
ThenThe heads and innards are removed and the fish goes into a weaker brine in barrels, kept at 15 to 18 °C (59 to 64 °F).
Early JulyCanning, for three to four weeks. The fish is still fermenting when the lid goes on.
Ten days before the premiereThe final product goes out to wholesalers.
Third Thursday of AugustThe premiere. Retailers sell the year's catch, and somebody fills a bucket.

A lease, a flight and a fire

Surströmming has a short and dramatic public record, and all of it is about pressure and neighbors.

Cologne, 1984

The landlord who brought a can to court

Wikipedia describes a West German eviction. In 1982 a landlord evicted a tenant for intentionally spreading surströmming brine on the edge of a witness's balcony and on the bushes in the garden. The tenant had already received a warning for spreading brine in the building's stairwell on the night of 24 to 25 December 1981. The tenant disputed the eviction, and in January 1984 the regional court of Cologne ruled the termination justified, after the landlord's party demonstrated their case by opening a can inside the courtroom.

The ruling, as Wikipedia quotes it, said the court “had convinced itself that the disgusting smell of the fish brine far exceeded the degree that fellow-tenants in the building could be expected to tolerate.” Note what the case was about: spreading the brine around other people on purpose, twice, after a warning. Eating a can was not on trial. An exhibit that argues for itself is rare in a courtroom.

April 2006

The airlines that said no

Wikipedia says several major airlines, among them Air France, British Airways, Finnair and KLM, banned the fish in April 2006, claiming that the pressurised cans were potentially explosive, and that the sale of the fish was subsequently discontinued at Stockholm Arlanda Airport. The people who make it called the decision “culturally illiterate” and said it is a “myth that the tinned fish can explode.” Neither side, in the article, mentions opening a can in the cabin to settle it.

2014

The warehouse

Wikipedia says that, due to the gases, a thousand cans of surströmming exploded over a period of six hours during a fire at a Swedish warehouse in 2014. That is the best evidence in the file for the airlines, with one caveat the file also supplies: it was a fire. The producers' claim is about cans in ordinary conditions, and we are not qualified to rule between a fish company and a fire.

How Swedes actually eat it

Outside, mostly. Wikipedia says that because of the strong smell, surströmming is often eaten outdoors, and that the pressurized can is usually opened some distance from the dining table, often punctured while immersed in a bucket of water, or after tapping and angling it upwards at 45 degrees, to prevent escaping gas from spraying brine. That is the first two options on the Neighbor Notice, and the reason the bucket is the low-tolerance choice there.

Wikipedia says the ungutted kind is gutted before eating and the backbone and sometimes the skin are removed. Then you build a surströmmingsklämma, the sandwich from the High Coast: two pieces of buttered hard tunnbröd, the fish, potatoes (sliced or mashed, often almond potatoes) and finely diced red onion. In the south it comes with gräddfil or crème fraîche, chives, and sometimes tomato and dill. Västerbotten cheese is sometimes added to counterbalance the fish. What to drink is disputed among connoisseurs, in Wikipedia's words, and the candidates are snaps, light beers, svagdricka, water and cold milk. The whole event is called a surströmmingsskiva.

The numbers, as Wikipedia gives them

Premiere: sales of the year's production were forbidden before the third Thursday in August by a royal ordinance sought by producers in the late 1940s. The ordinance is no longer in force, and retailers keep the date anyway.
About 2 million people eat it annually, per the Surströmming Academy's 2009 statistics.
Only 0.2 percent of all surströmming produced is exported.
Because it is made from Baltic herring, it contains higher levels of dioxins and PCBs than the EU permits. Sweden was granted exceptions from 2002 to 2011 and applied for a renewal.
As of 2023, with Baltic herring catches dramatically down, retailers sell out the whole supply within minutes of the annual release.

That last line is the one we find hardest to read. The world's most notorious smell sells out in minutes. So does everything we make.

Is it the smelliest food in the world?

Wikipedia says surströmming has one of the most putrid food smells in the world, even stronger than similarly fermented fish dishes such as hongeo-hoe, kusaya and hákarl. Here is what the same site says about those three.

Hongeo-hoe

Fermented skate, Jeolla province, Korea

Wikipedia says it emits a very strong, characteristic ammonia-like odor “reminiscent of an outhouse.”

Kusaya

Salted, dried, fermented fish, Izu Islands, Japan

Wikipedia says it has a pungent smell and is similar to the fermented Swedish herring surströmming.

Hákarl

Fermented shark, Iceland

Wikipedia says it has a strong ammonia-rich smell and fishy taste, making it an acquired taste.

That is a ranking by one encyclopedia, not a laboratory. We covered the one cheese with a real lab result in the smelliest cheese report, and surströmming is entry #3 on the Stenchi Smell Index, between the corpse flower and cadaverine. Another food that has cleared a building is covered in the durian report.

Questions people ask from a safe distance

What does surströmming smell like?

Several things at once. Wikipedia names the notes as pungent (propionic acid), rotten-egg (hydrogen sulfide), rancid-butter (butyric acid) and vinegary (acetic acid), and calls it “one of the most putrid food smells in the world.” It also says the smell is stronger than the Korean hongeo-hoe, the Japanese kusaya and the Icelandic hákarl, which are fermented fish dishes with reputations of their own.

Why does surströmming smell so bad?

Because the herring keeps fermenting inside the can. Wikipedia says Halanaerobium bacteria such as H. praevalens decompose the fish glycogen into organic acids, and that together with the bacteria, pungent-smelling acids form: propionic, butyric and acetic acid. Hydrogen sulfide is also produced, and carbon dioxide makes the can bulge. Wikipedia says a fermentation of at least six months gives the fish its characteristic strong smell.

Is surströmming rotten fish?

No, by Wikipedia's account it is fermented on purpose. During production just enough salt is used to prevent the raw herring from rotting while allowing it to ferment. The salt raises the osmotic pressure of the brine above the zone where the bacteria responsible for rotting can thrive. The result smells terrible anyway, which is a separate matter.

Can a can of surströmming explode?

The producers say it is a “myth that the tinned fish can explode,” according to Wikipedia, and they called the airline bans “culturally illiterate.” The same article says fermentation continues in the can, which bulges noticeably, and that a thousand cans exploded over a period of six hours during a fire at a Swedish warehouse in 2014. That was a fire, and the producers' claim is about ordinary conditions. We are not a food safety authority, we sell fictional deodorant.

How do you open and eat surströmming?

Outdoors, according to Wikipedia: because of the strong smell it is often eaten outside, and the can is usually opened some distance from the dining table, often punctured while immersed in a bucket of water or after tapping it and angling it upwards at 45 degrees, to stop the escaping gas spraying brine. The ungutted kind is gutted first, the backbone and sometimes the skin are removed, and it is eaten with tunnbröd (flatbread), potatoes and finely diced red onion.

When is the surströmming premiere?

The third Thursday of August. Wikipedia says producers lobbied at the end of the 1940s for a royal ordinance forbidding sales of the current year's production before that date. The ordinance is no longer in force, but retailers still maintain the date for the “premiere.” It falls on August 20 in 2026 and August 19 in 2027. Swedes usually eat it from that Thursday through early September.

Why did airlines ban surströmming?

In April 2006, Wikipedia says, Air France, British Airways, Finnair and KLM banned it, claiming the pressurised cans were potentially explosive, and the sale of the fish was subsequently discontinued at Stockholm Arlanda Airport. The producers called the decision “culturally illiterate.” We could not find an airline's own statement, so we only report what the article says.

What does surströmming taste like?

Wikipedia says fermentation gives the fish its “characteristic strong smell and somewhat acidic taste,” and calls it an acquired taste. It also quotes the German food critic Wolfgang Fassbender, who wrote that “the biggest challenge when eating surströmming is to vomit only after the first bite, as opposed to before.” Many Swedes like it, and many do not: it is more popular in northern Sweden than elsewhere in the country.

What does the word surströmming mean?

Swedish for “sour herring,” according to Wikipedia. Strömming is the Baltic herring, which is smaller than the Atlantic herring found in the North Sea. The ö is why most searches spell it surstromming. Both spellings mean the same fish, and the can does not care.

Is there a number for how bad surströmming smells?

You may see a score of 8,070 “AU” on lists of the smelliest foods. We could not trace it to a primary source we were able to read, so we do not use it. The only comparison we can source is Wikipedia's: its smell is stronger than hongeo-hoe, kusaya and hákarl. Nobody we could cite has put the cans in a room together.

More field reports

Surströmming is entry #3 on the Stenchi Smell Index, which is ten harder cases. These are the other reports from the Odor Research Division.

What does a skunk smell like?What does durian smell like?Why do farts smell?What do stink bugs smell like?What is the smelliest cheese?What does a corpse flower smell like?

Sources

Quotations are verbatim from the pages above. The Cologne ruling, the 2006 airline ban, the 2014 warehouse fire and the production and market figures are reported as Wikipedia states them; we did not read the court judgment or the original news reports. The jokes, the Neighbor Notice, the tolerance percentages and the Stenchi products are ours. This is a humor page, not food safety advice and not advice about how to treat your neighbors. Stenchi products are fictional and cannot be bought.

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