Ah. This is actually really obscure and appears to be something the author has simply made up on the spot. There's a famous story about how the Pharaoh Cleopatra made a bet that she could spend ten million sestertii (a Roman currency) on a feast, which she allegedly won by dissolving one of her priceless pearl earrings in a cup of vinegar and then drinking it.
Here, the author is using the phrase 'Cleopatra claret' to refer to really expensive wine - claret is a kind of wine, and vinegar is like decayed wine. 'Four pearls to the bottle' indicates wine that's even more ludicrously expensive than the stuff Cleopatra drank.
Hope this helps.