Food chemists uncover the secrets behind pretzels’ unique scent

Brezn, Brezeln, pretzels—whatever you call them, the knotted snacks smell different from other baked goods. Despite regional variations, all soft pretzels are chewy, salty, and have a shiny brown crust made by treating the uncooked dough with lye before baking. Sebastian Schoenauer and Peter Schieberle at the Technical University of Munich say that shiny crust is where the unique smell of pretzels—or they might say Brezn—comes from (J. Agric. Food Chem.2019, DOI: 10.1021/acs.jafc.9b02601).

The pair bought freshly baked pretzels from their local bakery and used gas chromatography/mass spectrometry and professional aroma assessors to identify the odor compounds in the crusts. They found 22 odor compounds that contributed to the beguiling scent, and then recreated the fragrance by dissolving the compounds in ethanol. The team next tweaked the recipe to try to find which molecules were key to the pretzel scent.

Phenylacetic acid, for example, is in pretzel crusts and hasn’t previously been found in other breads. But if Schoenauer and Schieberle removed phenylacetic acid from their lab-made pretzel perfume, their testers couldn’t smell the difference. After removing other scent molecules individually, the researchers found two molecules that are essential to the unique pretzel scent: 2-acetyl-1-pyrroline, which has a roasted smell, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone, which has a caramel smell. These molecules are found in other bakery scents, but the difference, the researchers say, lies in the proportions of the molecules, and that is influenced by the chemistry that goes on as the lye-treated crust bakes.