Pulque, a Traditional Mexican Alcoholic Fermented Beverage: Historical, Microbiological, and Technical Aspects

Abstract

Pulque is a traditional Mexican alcoholic beverage produced from the fermentation of the fresh sap known as aguamiel (mead) extracted from several species of Agave (maguey) plants that grow in the Central Mexico plateau. Currently, pulque is produced, sold and consumed in popular districts of Mexico City and rural areas. The fermented product is a milky white, viscous, and slightly acidic liquid beverage with an alcohol content between 4 and 7° GL and history of consumption that dates back to pre-Hispanic times. In this contribution, we review the traditional pulque production process, including the microbiota involved in the biochemical changes that take place during aguamiel fermentation. We discuss the historical relevance and the benefits of pulque consumption, its chemical and nutritional properties, including the health benefits associated with diverse lactic acid bacteria with probiotic potential isolated from the beverage. Finally, we describe the actual status of pulque production as well as the social, scientific and technological challenges faced to preserve and improve the production of this ancestral beverage and Mexican cultural heritage.

Keywords: Saccharomyces cerevisiae; aguamiel; dextran; fructans; lactic acid bacteria; maguey; probiotics; pulque.

Figure 1

Traditional pulque elaboration process. The traditional process involves four common steps: (A) Castration of the mature plant by cutting the floral bud and make the pit (cajete). (B) Pit scraping to promote aguamiel accumulation and sap extraction. (C) Seed preparation. (D) Fermentation. For details of the castration process see Supplementary Files 1, 2.

Figure 2

Aguamiel extraction from producing maguey, transportation to the tinacal and fermentation process. (A) Tlachiquero extracting freshly aguamiel with an acocote (Hidalgo state). (B) Aguamiel is transferred into a plastic container for transportation to the tinacal (Morelos state). (C) Freshly collected aguamiel appearance (Morelos state). (D) Aguamiel accumulated in cajete previous to the twice-daily extraction (Hidalgo state). (E) Aguamiel pouring into a plastic vat for seed preparation (Hidalgo state). (F) Fermented pulque in a plastic vat (Hidalgo state). (G) Fermented pulque in a traditional leather vat (Hidalgo state). (H) Serving pulque for direct consumption from the fermentation vat (Tlaxcala state). Note the characteristic filament associated to final product viscosity.

Figure 3

Microbial, metabolic and physicochemical changes during pulque fermentation. Proposed microbial, physicochemical and metabolic changes during pulque fermentation as described by Escalante et al. (2008). (A) Total CFU/mL counts for yeasts; (B) Total mesophilic aerobes (TMA); (C) LAB determined during 6 h fermentation in laboratory; (D) Sugar consumption expressed as mM hexose equivalent; (E) Fermentation products (ethanol, lactic acid, and acetic acid) expressed as mM C; (F) Cultivable diversity (% of four most abundant isolates); (G) Culture-independent diversity (% of four most abundant 16S rDNA clones); (H) Scanning electron micrograph corresponding to pulque fermentation after 6 h showing some yeast and short cocci chains (T6) (non-previously published photograph); (I) Aguamiel accumulated in cajete; (J) Fermented pulque. AM, aguamiel, T0, T3, and T6, the start of the fermentation, 3 and 6 h of cultivation, respectively. Ama, Acetobacter malorum; Ara, Acinetobacter radioresistens; Eag, Enterobacter aglomerans; Erh, Erwinia rhapontici; Ent, Enterobacter sp.; Kas, Kluyvera ascorbata; Lbh, homofermentative Lactobacillus sp.; Lbs. Lactobacillus sp.; Lac, L. acidophilus; Lla, Lactococcus lactis; Lme, Leuconostoc mesenteroides; Lci, L. citreum; Lki, L. kimchi; Sce, Saccharomyces cerevisiae; Zmo, Zymomonas mobilis; Uba, Uncultured bacterial clone.

Figure 4

Metabolic traits of main microbial groups present in aguamiel and during pulque fermentation. Main metabolic traits comprise homo- and heterofermentative lactic acid metabolism by LAB. Production of ethanol by Saccharomyces, non-Saccharomyces yeasts, and Z. mobilis. Acetic acid metabolism. Extracellular polysaccharide synthesis resulting in the synthesis of dextran and levan polymers by Leuconostoc sp. and Z. mobilis (levan). Microorganisms and metabolic pathways involved in the amino acid production, vitamins, and some antimicrobial compounds remain to be determined. Functional properties such as prebiotic and probiotic activities are related to fructooligosaccharide content in aguamiel and pulque or produced by LAB such as Leuconostoc sp. Probiotic properties are related to diverse LAB identified as Lactobacillus sp. and Leuconostoc sp.