'Irish stout Guinness must be served exactly 42 degrees from the equator, according to Roarty.Quality-control teams at the company say that the temperature should be 8 degrees, and not 50 degrees, as it seems.When used at a higher temperature, a creamy tan head with “yellows and hicks” looks like.'
https://acdc-beverage.com/what-temperature-should-guinness-beer-be-served-at/
Cold Guinness is a new thing. When were taught to pour Guinness we held the glass so the Guinness landed on the thumb to bring it to the correct temperature.