A look at the label can be revealing (NZ)

Whatever the price of a bottle of wine and the degree to which this influences the buyer, the label still plays an extraordinarily important role in its purchase. The label also provides the buyer with the other information that he or she wants and needs to know about the wine. Why the need, then, for a second or back label on the reverse side of the bottle? It is there to provide a warning to people who are allergic to certain foods, or are vegans and do not eat these foods, that traces could be present in the wine. The puzzling bit is how you get traces of fish, dairy products or eggs, the usual culprits, in wine, writes Warren Barton in The Southland Times.