According to the Senchus Mor, an ancient book of Irish law, Saint Patrick (b.~473 – d.~493 CE) employed a priest by the name of Mescan as his own household brewer. But what kind of beer would Patrick, patron saint of Ireland, have drunk?
First, it would have been an ale, rather than a lager. Proof of ale-brewing in Ireland comes from as far back as the sixth century CE. But it is certainly older than that as the Old Irish word for beer is cuirm, like the Greek korma, which indicates that beer has pre-Christian roots in Ireland.
The Senchus Mor, which is also known as Patrick’s Law (Cain Patrick) because he was responsible for having it compiled, indicates that ale was the most common intoxicating drink in Ireland, that it’s brewing was widely understood and practiced across the land, and that it was red in color. This ancient Irish law code also detailed the brewing process itself in some depth, describing the malting process and three quality control tests required for legally produced beer.
The main fermentable ingredient was malted barley, but other malted grains were also used, including rye, wheat, spelt, and oats. Brewers mashed with both whole and milled malts. Hops were not to be introduced as a flavoring in Ireland for roughly another thousand years, and ancient Irish ale may well have been served plain, though it is likely that aromatic bittering herbs and other ingredients such as red heather berries may have been used for flavoring.
The first mention of distilled spirits in Ireland doesn’t appear until 1405 when a chief named Richard MacRannall is noted as having died of an overdose of uisge beatha. The term “stout” wasn’t widely used to describe the beer style we associate with it today until around 1800 when Arthur Guinness’ brewery began marketing a stronger version of porter they referred to as “stout porter.”