four pearls to the bottle
Sorrows of the Millionaire
by George Bernard Shaw

.....
In the advertisements of the manufacturers of the country, I find that everything is produced for the million and nothing for the millionaire．Children，boys，youths，“gems”，ladies，artisans，professional men，even peers，and kings，are catered for; but the millionaire’s custom is evidently not worth having; there are too few of him．Whilst the poorest have their Rag Fair，a duly organized and busy market in Houndsditch，where you can buy a book for a penny，you may search the world in vain for the market where the 50￡boot，the special dear line of hats at forty guineas，the cloth of gold bicycling suit，and the Cleopatra claret，four pearls to the bottle，can be purchased wholesale．
How to explain"four pearls to the bottle "? Thank you for answering!

Question

four pearls to the bottle
Sorrows of the Millionaire                
    by George Bernard Shaw                           

.....
In the advertisements of the manufacturers of the country, I find that everything is produced for the million and nothing for the millionaire．Children，boys，youths，“gems”，ladies，artisans，professional men，even peers，and kings，are catered for; but the millionaire’s custom is evidently not worth having; there are too few of him．Whilst the poorest have their Rag Fair，a duly organized and busy market in Houndsditch，where you can buy a book for a penny，you may search the world in vain for the market where the 50￡boot，the special dear line of hats at forty guineas，the cloth of gold bicycling suit，and the Cleopatra claret，four pearls to the bottle，can be purchased wholesale．
 How to explain"four pearls to the bottle "?  Thank you for answering!

Answer

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.