Surströmming: “Sour Herring”

Rotten FishSurströmming is an ostensible “delicacy” common to northern Sweden. Referred to as “fermented* or “soured” herring, it is made by putting fresh caught fish in barrels to sit for a couple months, with just enough salt added to suppress the more nasty varieties of bacteria that would propagate in the slurry, otherwise. After two months, the fish is transferred to cans where the “fermentation” process continues, often causing the can to swell (which we in the U.S. would equate with the presence of botulism).

The swelling results from the production of carbon dioxide gas through the action of Haloanaerobium , a species of bacterium which feeds upon the fish.

Rotten Fish on Cracker-breadThe fish has such a foul odor that it is often opened and consumed out-of-doors. The smell results from the following compounds, produced during the “fermentation” period, which also add to the “complex” flavor of the product:

  • propionic acid: pungent/acrid quality
  • butyric acid: rancid-butter
  • hydrogen sulfide: rotten-eggs
  • acetic acid: vinegar-like

Praise it

Flush This
*Not accurate. The process of fermentation refers specifically to the biological action of organisms breaking down carbohydrates (as in grains, fruits, etc.). The processes which occur in animal products (which contain almost no carbohydrate) are properly called “putrefaction” and “rancidification.” It may be that purveyors of putrid, rancid flesh products adopted the term “fermentation” because 1.) The process superficially resembles the process of fermenting carbohydrates 2.) Because “fermented” sounds less noxious than “putrid” and “rancid.”

3 responses to “Surströmming: “Sour Herring”

  1. damn thats stinky

  2. I think fermentation could apply in this case. For example, production of yogurt is the fermentation of lactose by yogurt cultures that produces lactic acid, which acts on milk protein to give yogurt its texture and its characteristic tang. Sure, lactose is a form of sugar. But it makes up only around 2~8% of milk (by weight). Could it be a similar process for sour herring?

    • But that’s precisely the point. You ADD starter cultures to milk and control the temperature to make yogurt. Milk just doesn’t turn into yogurt by itself – it spoils. With the sour herring, nothing is being done but adding salt in a certain proportion. A sort of fermentation takes place because of the presence of lactic acid in the fish’ spine, but it is fermentation by autolysis, i.e., the cells of the fish begin to digest themselves. Autolysis CAN occur in beer or wine under the right conditions, but imparts an “off” taste that essentially ruins the product. Meanwhile, anaerobic bacteria are acting upon the fish to produce such compounds as butryic acid, a key by-product of rancidification (ever smelled rancid butter – that’s butryic acid you’re smelling) propionic acid (from the breakdown of amino acids), hydrogen sulfide, and related compounds, all of which result during putrefaction, and which are repsonsible for giving the fish its strong smell. Propionic acid and acetic acid, which are also produced, tend to prevent the growth of other bacteria, which explains why it doesn’t kill you. But it is not the lactic acid that preserves the fish or imparts the sour flavor, but rather the propionic and acetic acids.

      Technically, putrefaction IS a form of fermentation, but it is not the same process that occurs in yogurt, wine, etc….

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