Fruit at the discount grocery store is usually old/nearing end of life. Citrus, and limes in particular, get noticeably more bitter as they age and oxidize. Th

Fruit at the discount grocery store is usually old/nearing end of life. Citrus, and limes in particular, get noticeably more bitter as they age and oxidize. This actually leads to a schism in European/American bartending. Europe juices their citrus a la minute, so the juice has no time to oxidize, making the acid component punchier. American bars pre-juice before service, and it has time to mellow out a little. Someone (Dave Arnold maybe) ran a blind taste test with bartenders from Europe and America and found that the their preferences lined up with the customs in their country. Personally I follow the Europeans. Not because I like it better, but because I don’t have the kind of foresight to juice hours before I’m making drinks :-)