How do you tell if a woman is a virgin?

The gemara in Kesubos 10b has the following story. A newly married couple came to Raban Gamliel. The husband claimed that he had intercourse with his wife and she was not a virgin (because the husband saw no blood), she claimed that not only was she a virgin but she is still a virgin. Raban Gamliel performed the following test to determine if she was a virgin.

He took 2 women, 1 a virgin 1 not and had them sit on a barrel of wine. While sitting on the barrel he smelled their breath. The non-virgin's breath smelled like wine (because the odor of the wine went in through the opening and out through her mouth) while the virgin's breath did not smell of wine (because the odor of the wine could not get in because she was a virgin). He then performed the same test on the newly married woman and as her breath did not smell of wine proclaimed her a virgin.

This story is brought down l'halacha in Shulchan Aruch (Even Haezer Siman 68) and is discussed by the early Acharonim. Some of the acharonim discuss that this test did not already work in their day (one suggestion was that our wine is not strong enough).

The difficulty with the story should be obvious to everyone, we know now that this kind of test proves nothing and in fact is based on a completely false physiological premise. The fact that this story is quoted l'halacha indicates clearly that the gemara needs to be taken literally and cannot be reinterpreted as relating to pnimiyus hatorah etc.