The real issue with trying to recreate Viking food comes down, in the end, to aesthetics. We can know what they ate (from an ingredient standpoint) and what they used to cook those things because all of that stuff is still in the dirt. What we can’t know, and the part that’s hard to even theorize about, is what their aesthetic was like.
Every cuisine has some fixed aesthetic that transcends recipes. If you’ve cooked enough Italian food, for example, you can make new dishes that fit within an Italian food gestalt without having a specific dish. One of my biggest goals is to try and get a handle on what they Viking food gestalt was like.
Because the “Vikings” were geographically spread over such a wide area, there must have been wide variations in what their food was like. The environment and available materials in the Danelaw or in Denmark (or Byzantium, obviously) are much different from what would have been available in Iceland or Trondheim.
One of the influences (if that’s the right word) that we can take a pretty good guess about is lactic fermentation. In a cool Northerly climate, pretty much anything that’s wet will sour eventually. Vegetables, grain, dairy products, and possibly meat and fish all can be soured. The farther North you get, the harder or more expensive it is to get salt, so sour flavors enhance the taste of food in lieu of salt.
Given the above, I think the “Viking” diet (if we can even characterize it as such) would have contained more sour flavors that we are used to in our modern American diet. Grain-based porridge, if soaked overnight or longer in water will sour, particularly if it is soaked in a wooden or pottery vessel that is impregnated with lactobacilli. There are modern or early modern equivalents to be found in the oat porridge of Scotland and the millet porridge of Africa, both of which have traditionally been allowed to sour. There are numerous examples of sour dairy products such as cultured or clabbered milk, “sour cream”, etc. Syra (soured whey) was commonly mixed with water as a drink in (at least medieval) Iceland.
Given that, and bearing in mind some of Daniel’s musing on sweets I think the Viking aesthetic probably involved more sour, and less sweet and salty flavors that we are used to in modern America. Aside from that, I still have plenty of thinking to do.