Studies with ¹³C-2 labeled glycine in model systems containing 3-hydroxy-2-butanone or glyceraldehyde have indicated that the β-dicarbonyl compounds, the immediate precursors of pyrazoles, are produced in Maillard model systems through two pathways. One pathway involves dehydration of α,β-dihydroxy carbonyl compounds with elimination of the α-hydroxyl group and the other through aldol condensation of an α-hydroxy carbonyl compound with simple aldehydes to produce α,β-dihydroxy carbonyl moiety that can undergo the above-mentioned dehydration to produce β-dicarbonyl structures. The conversion of β-dicarbonyls into pyrazoles can be achieved through 1,3-diimine formation by reaction with either two ammonia molecules or with a primary amine and an ammonia. After imine–enamine isomerizations the resulting dienamine can be oxidized to form pyrazole rings similar to the oxidation of two thiol moieties into disulfide linkages. The α-dicarbonyl species can serve as hydrogen acceptors since in their absence no pyrazole formation was detected. Glycine/3-hydroxy-2-butanone system generated 3,4,5-trimethyl-pyrazole (associated with the aroma of tequila) and 1,3,4,5-tetramethyl-pyrazole whereas, glycine/glyceraldehyde generated 1,5-dimethyl and 1,3,5-trimethyl-pyrazoles.