WHICH IS NOT TO SAY that tequila has completely lost its reputation as firewater, the go-to slam juice for frat boys. But Tim and I are past all that (yeah, right), so we set up our trip more like a Napa Valley wine tour. With the help of guide and designated driver David Ruiz, a well-connected 58-year-old who retired from Silicon Valley to lead custom tequila tours, we carefully scheduled the first three and a half days and left the last two and a half free for "follow-up." Tim, a 32-year-old wine importer from Colorado, would function as our professional taster-think of him as the Nose.

Leaving Guadalajara at 8:30 A.M. on opening day, we exited Highway 15 at Arenal, the start of La Ruta, crossed over a river green with sludge, and parked at our first small distillery, Fabrica de Tequila Cascahuin, which recently began producing a $700 limited-edition tequila called Revolución Oro. Inside, we saw that the fermented agave traveled to the distillation tanks through an open ditch in a concrete walkway, so we didn't stay long enough to taste it. Mistake. By early afternoon, we realized that a lot of tequila, including some great stuff, is produced under conditions that look pretty disgusting. We decided to spend more time drinking and less time peering at factory floors.

We became wonks, noting "slow legs" and "long finishes," "amber hues" and "hot burns." Experts will tell you that the differences in sipping tequilas are not as dramatic as they are with single-malt Scotches, but we found more than enough subtleties to keep us fascinated-hints of brown sugar, honey, pepper, butter, cabbage, sweet potato, cooked banana, apricot, apple, lemon, pear, mint, strawberry, coconut, and apple blossom. Alas, Tim forbade me to use the word ambrosia.

On our second day we tasted 17 tequilas and found ourselves agreeing with the cognoscenti: The tequilas on La Ruta taste more herby, while those from the highlands are more floral. We also developed two theories of our own. First, that tequilas produced by the big tequila houses tend to be more approachable, because they taste pure, while the product from smaller manufacturers tends to have more character, more varied flavors. Second, that an aged tequila is the highest form of the art.

This came to us while tasting what proved to be our favorite, a stellar extra añejo called D'Antaño de la Casa Siete Leguas. In many aged tequilas, the agave flavor is buried under sweet oak, or it appears out of nowhere, a come-hither look followed by a slap across the face. But this rare five-year crescendoed through toffee, caramel, pear, and banana to a twinkling high note of slightly peppery agave, then faded back to sweet and slowly away.

And did I really just say that? Hmmm. I think it's time to put down my stemware and holster the similes.