This is what I've found so far in terms of evidence for actual dairy consumption...
As for the Germanic tribes, Tacitus, if he can be trusted, says that they consumed fruit, game and curdled milk. Would that be fresh cheese or a yoghurt like substance? They must have consumed meat from their herds as well, but he doesn't mention it.
Other ancient writers just said meat, milk, and beer. I don't know if that was curdled milk or just plain milk.
In medieval times, according to this book, extent records of doctors, some manor records etc., seem to indicate that it wasn't consumed very much among the upper classes except for the very young and very old (problems with their teeth?). The main concern seems to have been that it spoiled so quickly. Also, the ownership of a cow seems to have been beyond the means of many serfs. The milk from the herds of the manor seems to have been used for butter, which, along with lard, was a cooking fat, and cheese.
http://books.google.com/books?id=Ve...onsumption of milk in medieval Europe&f=false
This article finds no evidence for much actual milk drinking at all, but I can't find the original source upon which this translation is based.
http://www.eps1.comlink.ne.jp/~mayus/eng/MariaEng.pdf
While this book agrees that milk consumption was discouraged in adults in the medieval world, it does say poor people consumed it, but whether as whey in food isn't clear. In other words, the serfs would have gotten the leavings.
http://books.google.com/books?id=jt...ge&q=drinking milk in medieval Europe&f=false
This paper discusses the huge increase in milk consumption in the 19th century in Barcelona as the result of better and faster transportation and pasteurization.
http://scielo.isciii.es/scielo.php?script=sci_arttext&pid=S0211-95362010000100005
I can't get access to the book, so this is a second hand account:
" For England alone the answer would vary according to class
(dairy products had low status - the aristocracy avoided them, the
poor had no choice but to depend on them), region (some areas
emphasised pastoral farming, others arable), season, and period (the
balance between arable farming and pastoralism fluctuated, especially
before and after the Black Death - though ironically the expansion of
pastoralism after the plague was parallelled by rising peasant
prosperity, causing them to ape their betters by rejecting dairy
products).
Chris Dyer's 'Everyday Life in Medieval England' (London, 1994) has a
chapter, originally a 1988 Agricultural History Review article, which
discusses medieval peasants' diet and at pp. 82-3 analyses harvest
labourers' food allowances on a manor in Norfolk between 1256 and 1424
- the dairy element in these varied between 28% and 9% in terms of
value and 13% and 7% in terms of calories (though the calory data
include eggs with the dairy produce, for some reason).
He revisited the subject, and looked also at aristocratic diet, in
'Standards of Living in the later Middles Ages: Social Change in
England c.1200-1520' (Cambridge, 1989). At p. 56 he analyses several
14th- and 15th-century aristocratic households' diets - dairy produce
amounted to only 1-3% by cost.
I'm quoting this 2012 book, which is pretty venomous in my opinion about the "barbarian tribes", just for the section where he discusses the different classes at the bottom of society. He specifically points out the areas where tenant farms existed. It seems to me that in that situation, the tenant farmers might indeed have kept some of the fresh milk for themselves.
http://books.google.com/books?id=Mn...ge&q=dairy farming in medieval Europe&f=false
Bottom line, it seems that the Germanic tribes did consume dairy, but whether most of it was curdled, I don't know. When they were traveling it seems that they might have milked the cows, at least during the summer months after they calved.
The medieval period seems to have been one where milk drinking was not very popular among the upper classes, but butter and cheese were certainly used by everyone, and became a part of commercial exchange. Perhaps it was a situation where the poor serfs made do with some leftover buttermilk and whey? Tenant farmers might have been in a different situation. However, it seems to me from these papers that the widespread drinking of cow's milk is a very recent development, which I didn't previously understand.