If you Google "Irish butter", I think this blog is the 7th reference on the page. That's kind of big. I get more international hits for my, "What's Irish Butter Got That American Butter Ain't"? entry than any other entry. Second place is any entry with the name "Christian Bale" in it. For real. I get hits every single day from countries all over the globe looking for, I guess, clarification on what exactly constitutes Irish butter.
If you go to "http://www.answerbag.com/q_view/1962097", you will find information on what makes butter Irish. This information is supplied by Kerrygold Dairies. Here's what you'll find:
Like several European-style butters, Irish butter has a higher butterfat content than used in American butter. As a result, Irish butter melts more easily and at lower temperatures for cooking.
Irish butter has a smoother, creamier texture than American butter. It tends to be less waxy than its American counterpart.
Because of its high butterfat content, Irish butter takes only 15 minutes to come to room temperature and easily burns when used for frying foods. Blended into pie crusts and pastries it produces a flakier product and is particularly well-suited for flavorful whole grain home-baked breads.
Irish butter has a richer, almost cheesy, character. It tends to be saltier and less bland than American butters.
Irish butter is a startling golden sunshine yellow color, far more yellow than the whitish butters found in North American varieties.