(NPR) - In a laboratory, deep under a mile-high stretch of the Alps on the French-Italian border, Philippe Hubert, a physicist at the University of Bordeaux, is testing the authenticity of a bottle of wine.

"We are looking for radioactivity in the wine," says Hubert. "Most of the time the collectors send me bottles of wine because they want to know if it is fake or not."

First, Hubert takes the bottle in the hand and puts it close to a detector. After he closes the shielding, which blocks the radiation, he records the gamma rays. The level of those gamma rays emitted can often tell him something about when the wine was bottled. For example, if it was bottled before about 1945, there shouldn't be any cesium 137 — radioactive evidence of exploded nuclear bombs and the Atomic Age — in the wine.

But that's not the only way to do it. Maureen Downey, wine detective and founder of Chai Consulting wine appraisal and authentication in San Francisco, has a toolkit of items she uses to forensically examine bottles of wine — razor blades, magnifying glasses, jewelers loupes, flashlights, blue light.

"Counterfeit wines have become a much bigger problem of late," says Downey. "In the last year, I myself have written reports for about $5 million worth of fakes."

And as fraud goes up, experts are going to greater lengths than ever before to authenticate wine — the fibers of the label paper, the tiny pits in the glass, the depth of the punt in the bottom of the bottle, all hold clues. And so do the corks.

"Fraudsters put a lot of work into trying to make their corks look distressed," says Jancis Robinson, a longtime wine writer for The Financial Times. "It's important that the label look like it's been around the block a bit, so they might rub it with a bit of earth or coffee grounds."