I've been "making cider" with the left over yeast cake from whatever beer I happened to rack to keg. I typically go buy 4 gallons of AJ and just dump and stir it up real good. Usually comes out pretty decent for basically hooch.
The last two I did I left in the primary for 4 weeks. Two weeks longer than my typical ferment. I racked them to kegs and carbonated with CO2 as usual. These two have almost zero taste.
It tastes pretty good when I mix in 1/2 a glass of regular AJ. Could I pour a gallon or so of regular AJ in the keg or do I need to boil it first?