Abstract
This study evaluates the simultaneous effect of dried starter concentration and fermentation duration on the quality characteristics of the African opaque sorghum beer using response surface methodology. The aim was to improve the beer quality and to optimize its fermentation process. Results show that the granule starter concentration and the fermentation duration have significant effects on the dry matter, refractive index, titrable acidity, glucose, raffinose and fructose contents of the beer. The lactic acid bacteria, yeasts and total mesophilic aerobic bacteria counts were significantly modified as a result of these fermentation parameters. The pH was only affected by the fermentation duration. The optimum beer quality could be reached between 10 and 15 h at starter concentration in the interval of 100 to 120 g/L. The use of the dried starter granules revealed to be an efficient alternative to produce sorghum beer with stable quality at a shorter fermentation time. Key words: starter, kpete-kpete, sorghum beer, tchoukoutou.
Highlights
Opaque sorghum beers significantly contribute to the diet of millions of people in Africa due to their relatively low alcoholic content and high dry matter and nutrients concentration (Novellie and De Schaepdrijve, 1986)
This study evaluates the simultaneous effect of dried starter concentration and fermentation duration on the quality characteristics of the African opaque sorghum beer using response surface methodology
Several researches reported that the microorganisms contained in the traditional starters of African opaque beers mainly consist of yeasts and lactic acid bacteria (LAB) (Van der Aa Kühle et al, 2001; Demuyakor and Ohta, 1991; SefaDeheh et al, 1999; Sanni and Lönner, 1993)
Summary
Opaque sorghum beers significantly contribute to the diet of millions of people in Africa due to their relatively low alcoholic content and high dry matter and nutrients concentration (Novellie and De Schaepdrijve, 1986). The slurry is mashed under gradual heating until the boiling point is reached after 2 h, mixed with supernatant and allowed to ferment overnight, filtered, boiled (6 to 9 h), cooled, and inoculated with a starter called kpete-kpete, which is generally harvested from the bottom of a previous fermenting beer (resulting from 13 to h overnight fermentation). The microorganisms are kept alive by replacing the supernatant on a daily basis. The preservation of such starter is a tedious and a risky business since it is common that the starter loses its fermenting properties and fails to make the beer effervescent, as a result of the death of the involved microorganisms
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