There’s little agreement anymore on what should or should not go into an Irish stew. The meat in the stew would have always been “sheep”, as sheep was what they raised — lamb, or more probably, mutton. (Though well before that, the meat would actually have been kid — as in young goat.) When the Irish came to America, though, they would have adapted: after all, Irish stew was about using what you had, and that would have been beef, so now there are versions that use beef or lamb.
Should you think beef is a “new heresy” for Irish stew, having only been happening, oh, since the early 1800s or so, you might want to get excited about the potato, too. Potatoes weren’t generally available or accepted in Ireland until the mid 1600s, and so wouldn’t have been part of Irish stew originally, either. The stew would have been thickened with barley, or with pieces of a bread such as oat bread broken up into it. By the early 1700s, the Irish had definitely switched to using potatoes to thicken their stews instead.
Some recipes will have you layer the ingredients, but this may be North Americans confusing Irish Stew with pictures of Lancashire Hot Pot. Most will just have you toss stuff in and get on with it. In all recipes, the stew is stewed for hours, and ends up very thick.
Some recipes will call for dumplings (Ireland got baking soda in the 1840s.)
The addition of Guinness is most certainly a modern innovation, as country folk in the 1800s wouldn’t have always had tins of Guinness Draft sitting in the fridge, but nevertheless, it is a most welcome innovation.
The earliest written reference that we know of to Irish Stew was in 1812, by Lord Byron in an unfinished poem:
“The Devil returned to Hell by two,
And he stayed at home till five;
When he dined on some homicides done in ragout,
And a rebel or so in an Irish stew.”
Literature & Lore
“Wipe and cut in pieces three pounds lamb from the fore-quarter. Put in kettle, cover with boiling water, and cook slowly two hours or until tender. After cooking one hour add one-half cup each carrot and turnip cut in one-half inch cubes, and one onion cut in slices. Fifteen minutes before serving add four cups potatoes cut in one-fourth inch slices, previously parboiled five minutes in boiling water. Thicken with one-fourth cup flour, diluted with enough cold water to form a thin smooth paste. Season with salt and pepper, serve with Dumplings.”
— Fannie Merritt Farmer. The Boston Cooking School Cookbook. 1918.
In Irish, the stew can be referred to either as “ballymaloe” or “stobhach gaelach”.