The question of Yule, its origins, pre- and post-Christian forms, festivity and drink, are far beyond our scope here.
Nonetheless I have now reviewed dozens of 19th century references in general literature to Christmas and ale. I thought there had to be a proximate cause, at least, for the association.
There is, or so I conclude, it is St. Thomas’ Feast Day. St. Thomas of course is one of the 12 apostles. December 21 was originally his day, one devoted to Christmas preparations. The date was later changed in the Catholic calendar to July 3, but some Anglicans still remember the earlier date.
December 21 (this Monday) is the Solstice, the shortest day of the year in our part of the hemisphere. On that day in England and many parts of northern Europe, Christmas preparations began: preserving, baking, mending garments or tools, etc.
John Harland, in a journal of archeological and religious history in 1865, explained the old practice of recording the days by pictograms on sticks or staves. In a chronology drawn from one of these, December 21 is the day the “Christmas ale” was brewed. Often, a barrel was engraved to convey the significance to a pre-literate society.
A modern (2017) blog account of St. Thomas’ Day references the tradition especially in a Norwegian context, but it existed in many northern places. The different names for the stick have recognizable variants in the different places.
Messedag stick was one term known in England (Mass Day). The blog account includes an image of a stick (portion) showing a barrel with drinker for 21 December. A second stick appears to depict a tub of some kind, for mashing or fermenting on that date.
Other accounts suggest that in Norway, the beer was actually tasted on December 21 and hopefully pronounced good, with brewing taking place earlier in the month. Some explanations suggest the beer was subjected to fermentation on December 21, so broadly brewing again.
One way or another the day was connected to the beer to be enjoyed at Christmas and through Yule-time.
Of course such beer would be “mild” by Christmas, meaning newly brewed. This does not mean all Christmas beer was new beer.
But the fact that freshly-brewed (mild) beer was often associated with Noel, probably in many cases made from carefully husbanded ingredients, shows a connection to St. Thomas Day, in our view.
According to the Harland account the Winterside of the stick reflects that for January 13, the 20th day after Christmas, “the Christmas ale is then finished”. The pictogram is an upturned horn or barrel. Points for clarity to the craftsmen of these devices.
So this gives some idea how deep is the taproot of Christmas and ale, in those parts of the world. Is there a straight line to Hallett & Abbey’s Christmas Mild Ale of 1857-1860? No, but it’s all connected.
Unlike much that concerns brewing history, beer style is not the point here. The type of beer would have varied depending where and by whom it was made.
The keynotes are brewing as such, the Yule period, and Christianity.