One of the first things anyone says at every public demo we do about Viking food is “oh, lutefisk!  Gross!”.  The Vikings did not, in fact, have any lutefisk.  What they had instead was stockfish, which is unsalted cod dried hard as a board.  Much later, the Scandinavians figured out that stockfish was more easily edible if it was soaked in lye water until it softened, producing lutefisk at last.

The real fallacy here, though, is that whatever our Norwegian/Swedish grandmothers cooked must have been what the Vikings ate.  Much of what we think of as “traditional” Scandinavian cooking probably didn’t mature in it’s present form until the early modern period, 300-400 years ago.  There are New World ingredients such as potatoes (lefse, mashed potatoes, Jansson’s Temptation, klubb…) or beans that figure prominently in modern folk cooking in Scandinavia. 

That isn’t to say that there is nothing to learn from modern Scandinavian cooking.  The constraints such as short growing season, limited arable land, high consumption of dairy products, etc. applied just as much to Scandinavia 400 years ago as they did during the Viking age.  However, that only helps us when taken in aggregate as it applies to the whole cuisine.  Any comparison between modern dishes individually and potential Viking age equivalents can only lead to error.