I got the story from Eric Illott, and it was definitely brandy. Brandy was reserved for the officers, and jealously guarded - the level in the barrels was recorded, and woe betide the crew if any was missing. Some bright spark on the Victory's lower decks realised that the barrel with the Admiral in wasn't going to be opened until they reached London, when the crew would be paid off and have a chance to get away before the deed was discovered. Apparently there wasn't a drop of brandy left when the barrel was opened. Like any story (or song) that has been through the oral transmission process, I wouldn't take it too seriously as history, but never let the facts get in the way of a good story (as our local paper says).