Possible Clues:

• Grain used in brewing
• Grain some animal took
• Island wanting a source of whisky and beer
• Rat's food, in 'The House That Jack Built'
• Island finally runs out of top grade whisky
• Drink with a foamy head
• What the rat in Jack's house ate
• Grain prepared for brewing or distilling
• Brewmaster's buy
• Lose feathers, say, when given barley