Caught in the months of May and June, processors immerse the fish for a day in brine and then decapitate and clean it. Next they stack it in barrels, trundling it out into the summer sun and left there for 24 hours to get the fermenting process started. An inch or two of space is left at the top of each barrel so that any gas formed during the fermentation can accumulate with out causing an explosion.

Put into a cool storage room, the herring ferment at a slower rate. As they do, their aroma grows progressively stronger, and only the most acute nose can determine the precise point at which they are ready for canning.

Among those who like surstromming best, and its fans are many, there's the belief that the contents of a can left for a year at a temperature of 68̊ F. actually improve; the can will have begun to swell, and at its puffiest must be opened gingerly, like a bottle of champagne.

Swedes eat ripe surstromming with paper-thin hard bread and boiled potatoes, usually an almond-shaped variety that comes from the north. It has a sharp, cutting taste. Sometimes, they drink milk with it, but beer and aquavit more often accompany the dish. Some Swedes down it without a second thought to its smell; others, in order to partake of it at all, first have to rinse it in purifying soda water.

Sales of surstromming are on the increase in Sweden, but its future as an export item is, predictably, dim. Although 800 cans of it used to be exported annually to Hollywood when a Swedish movie colony could still be found there, U.S. customs officials have since come to view it with suspicion, despite its proven nontoxicity. Moreover, the product doesn’t always travel well. Only recently a Swede found this out. Thinking to amaze an important New York client and the assembled board of directors with so bizarre a food, he produced the swollen can he had carried all the way from Sweden in his luggage and dramatically laid it on the table. At that moment, the can exploded.