I currently detect zero threads in the history section and I am 3 months out from certification, so I almost have to start something on here.
Hello, I am a crazy person who does a lot of reading about the Dark Ages. I can answer questions or provide updates on information I have found. I am also working on a Dark Ages wargame with a few others (Has its own website), and I have a multi-faction "kingdom builder" campaign. So I discover things while trying to do research for the stuff I'm responsible for.
I know the most about areas we have the least information written by the OG sources, and the maximum portion of that is in English.
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Food Facts 1, North Europe
Despite what Total War or Civilization might imply, agriculture was not uniform in capability over Europe. The parts around the Med Sea were very fertile and like Mexico/Brazil/Florida today, places where specific things could be grown. At the same time, the soils were soft and easy to work with "scratch plows" made mostly of wood.
The people of around Northern Europe, Britons, Scandinavians were in a tough spot. The soil is hard and more advanced plows won't exist till around 700-900. More advanced blades for the plow, more advanced mechanisms, and the means to have a cheap, plentiful work horse do the pulling (Oxen are expensive, hungry beasts, slow too)... Will not fully be available till 900-1000.
Oh and people had a two field crop rotation system: growing food or fallow. The period of 700-900 sees the introduction of a three field system, where they plant beans or high protein, high put nitrogen in the soil crops as the step after or before grains.
Britannia struggled to grow Wheat, but Rye I think was introduced by the Saxons and that with Barley, oats grew pretty well. Bread, soaked grain, "table ale" was 90% of the diet or more. If you've heard of a "beer gutt" imagine if all you drank was like calorie filled, low alcohol beer, thats a table Ale. It has no hops in its making, mostly malt and barley/rye. People who did heavy, respected work was drink like a few liters of this a day.
I'm pretty sure that the most common meat was sheep, the most common cheese was "cottage cheese" (Hence the name) from goats or cows. In Ireland most trade is with female slaves and cows, and in Francia (France) I see gold soldini worth about a cow each.