African traditional brews: quality, chemical constitution and health aspects.

Wide quality variability, unpredictability and lack of routine scientific quality control in African alcoholic beverages leads to uncertainty in the identity and quality of what is being consumed. The problem is important as these products are mass consumed and command the largest market share in the alcohol market. Ethanol, the target of fermantative conversion of sugar, is variable both within and between brands and ranges from ca. 3.5 to 8.2 % v/v in brews examined in this work. Fluctuating levels of unwanted fermentation by-products have been detected: methanol (0.3 - 3.2 ppm), butanol (9.8 - 39.6 ppm), propanol (10.6 - 51.4 ppm), isoamyl alcohol (42.5 - 231.6 ppm), furfural (56.8 - 412.3 ppm) and acetaldehyde (10.7 - 44.9 ppm). Metallic contaminants in some traditional brews have been found to exceed the WHO and Tanzanian Standards (TZS) for drinking water. In about 25 % of the processing water samples analysed, cadmium levels exceeded the WHO and TZS limits. Zinc levels in processing water were lower than the specified limits. Nutrient levels like fats range between 0:028 - 0.585 %,w/w while the levels of carbohydrates range between 3.395- 11.036 %,w/w. On average, protein content is high in maize/cereal based types but lowest in plant sap derived brands. Traditional brews generally have higher calorific value than Tanzania Breweries Ltd (TBL) brands. However, when the ethanol calorific value is included, the values double. This means consumers derive ca. 50% of their calorific needs from this objectionable source. Bacterial contamination for coconut palm wine brand averages of 11.20 ± 4.15/100 ml faecal coliform (F.C.) and 113.20 ± 11.4 /100 ml total coliform (T.C.). Some processing water samples have recorded high coliform (T.C.) 3,629.50 ± 440/100 ml (F.C.) 241.00 ± 22.5/ 100 ml). Contamination is not traceable to the plant sap but to handling. The quality of brew is dependent on shelf life and temperature. The quality however, continues to deteriorates and attains a critical shelf life at 17 hours (30°C), while at 40°C, this status was attained after 12 hours. At 17°C this is lengthened to ca. 32 hours. The levels of furfural increase with extent of fermentation. Rise in temperature favours the formation of furfural via the Amador Rearrangement Product (ARP) via 1,2,-enolisation. The concentration of protein decreases with shelf life where the rate is high in the first 10 hours, probably this interval is dominated by formation of Free a- Amino Acid (FAN).