When drinking fine tequila, look for a clear or light yellow color, a smooth taste and a hefty dose of methanol, 2-methyl-1-butanol and 2-phenylethanol.

The presence of these three chemicals is significantly higher in tequila made from 100 percent blue agave, a spiky succulent plant that grows in Mexico, and now scientists have developed a test to determine whether tequila is pure or "mixto" with sugar.

In a statement timed to coordinate with the Mexican holiday of Cinco de Mayo, or May 5, the American Chemical Society said it was publishing research on a quality assurance test for tequila in the June 14 issue of the Journal of Agricultural and Food Chemistry.

"Tequila is one of the best regulated spirits in the world, with strict Mexican standards and labeling regulations," study leader Dirk Lachenmeier said in the statement. However, the researchers said adulterated samples have been reported.

To guard against this, they analyzed the chemicals in 31 samples of 100 percent blue agave tequila and compared the results to 25 mixed-tequila samples.

The pure agave versions had higher levels of methanol, 2-methyl-1-butanol and 2-phenylethanol, the scientists found.