SWMBO and I made up a Guiness Ice Cream last week. It called for reducing the Guiness over a low simmer to 3/4 volume, then adding it into the custard prior to running it in the machine.
It turned out okay, but there were loads of ice crystals after freezing. Our next attempt at this we will use our own Stout brew which is fuller bodied than the Guiness and reduce it to 1/2 volume.
I don't have the recipe here at work, but if my memory recalls it was something like this:
2 cups heavy cream
1 cup whole milk
6 egg yolks
1 cup sugar
1 vanilla bean (split with seeds removed and added to mixture along with bean hull)
12oz Guiness Beer
Reduce the Guiness on a low simmer to 3/4 volume and cool in the refridgerator
In a large sauce pan heat the heavy cream, milk, sugar and vanilla to a light boil. In a separate bowl beat the egg yolks and slowly add 1 cup of the cream mixture to the eggs while wisking (you do not want scrambled eggs so be careful). Add the egg and cream mixture to the sauce pan while wisking and bring the mixture up to 170F. for 5 minutes (wisk or stir constantly). Cool the mixture for 2 hours in the refridgerator.
Add the Guiness reduction to the cooled custard and place in the ice cream machine.
Pack ice cream in containers and put it in the freezer for at least 1 or 2 hours.