Surströmming (sour herring) is the name given to a fermented can of fish which once opened can clear a room in seconds.
Here's the technical bit about why it smells so bad:
Surströmming was created long ago, when brining food was quite expensive due to the cost of salt. When fermentation was used, just enough salt was required to keep the fish from rotting. The salt raises the osmotic pressure of the brine above the zone where bacteria responsible for rotting can thrive and prevents decomposition of fish proteins into oligopeptides and amino acids. [source]Basically it ferments in the can like a forgotten yougourt left in a school locker over the summer holidays. Then, just as the tin bulges and buckles under the built up pressure you open it and serve it as a meal.
Can you see how much the tin has expanded!?
Apparently a Japanese study has shown that the smell of a newly opened can of surströmming is the most putrid smell of food in the world. So what was Farfar thinking when he made us close all the windows and doors and open the can inside the house???
Perhaps unsurprisingly this traditional food is served with strong vodka. Here is Farfar enjoying his fragrant fish supper. "Mycket gott!" he said as we all held our stomachs.