It was in the barrel, yes. You use the soap.
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The barrel was the key. I had tried everything I could think of to clean the mold off the barrel and all I had to do was USE soap. I wish authors wouldn't use USE. It's a real cop-out. This game uses it a lot.
Anyway, once I had the big jerky, the rest of the game was a doddle. I've finished now.
P.S. Don't use the flask on Dennis, as you need it somewhere else.