chestnuts
In southern Europe in the Middle Ages, whole forest-dwelling communities which had scarce access to wheat flour relied on chestnuts as their main source of carbohydrates.

To preserve chestnuts to eat through the winter, they must be made perfectly dry after they come out of their green husk; then put into a box or a barrel mixed with, and covered over by, fine and dry sand, three parts of sand to one part of chestnuts.