Apparently it's a secret recipe and was originally stored for 21 years before being drunk (two pints down in one) in a strange initiation ceremony involving men eating radishes and standing on one leg. Until in the 1870s the lure of free beer was too much and the young men of Kendal started trashing the place.
It's a decent example of a strong(ish - only 5.5%) sweet slightly spicy beer. I'd guess the original recipe was brewed much stronger, and it could do with more alcohol. It's now brewed over 50 miles away on the other side of the Pennines and
is available in Waitrose, as well as at Levens Hall (recommended - a stately home that feels lived-in and homely, despite some of the best panelling and leather wall-hangings you'll ever see.)