Investigation of chemical constitution and impurities in traditional brews consumed in the Dar es Salaam area.

Local brew brands from the Dar es Salaam area have been examined for their chemical constituents, impurities, quality parameters, the mode of brew deterioration with shelf life, and factors influencing metal uptake from container surfaces to the brew. Various constituents of human health concern have been identified. No strict specifications are discernible within samples of the same brand. The quality data is characterised by large variability and attendant quality unpredictability. Alcohol levels fluctuate widely from as low as 2% (v/v) (mbege) to 8.3% (v/v) in wanzuki while in moonshine spirits levels range between 21 to 44% (v/v). Sugar content varies between 4.0 - 9.5% (w/v) except in high - alcohol brands which are devoid of sugar. Discernible reverse trends are observable between alcohol and sugar thus the greater the alcohol strength the lesser the sugar content. The quality of brew changes with time as the alcohol content increases progressively with continued fermentative conversion of available sugar to alcohol. The quality however, continues to deteriorate and attains a critical shelf life (18 hours in Dar es Salaam) beyond which it is unacceptably objectionable. Moonshine contains substantial quantities of fusel oils (up to 800 ppm butanol) and methanol (in the range of 150 ppm). Ester levels differ from brand to brand but are a maximum in moonshine spirits. In banana brew (mbege), ester levels are noticeable due to the presence of iso-amyl acetate associated with banana aroma. Acetaldehyde up to 122 ppm is recorded in wanzuki. High acidity is a general ch~uacteristic of local brews and increases with shelf life. Predicted conductivity trends paralleling increasing Total Dissolved Solids (TDS) values are blurred due to substantial varying sugar (non-electrolyte) levels in traditional brews. Density correlates with alcohol strength in non-turbid products i.e. varies inversely with alcohol strength. Lack of stringent filtration procedures is partly responsible for high Total Suspended Solids (TSS). Continued fermentation in the ready product due to un-removed yeast leads to quality changes as the product ages. Metallic contaminants in some local brews have been found to exceed the WHO standards for drinking water. High levels of lead (over 0.8 ppm) have been recorded in bamboo wine. Alarming amounts of cadmium are observable in some brands including kimpumu and coconut palm wine (0.78 and 0.64 ppm respectively). High copper levels (upwards of 30 ppm) are reported in moonshine spirit. The zinc load is < 15 ppm (i.e. below WHO maximum. permissible level for zinc). Substantial amounts of iron (up to 115 ppm in coconut palm wine) have been found in most brews. While acidity (the principal determinant of metal dissolution), shelf life and temperature enhance metal uptake from container surfaces, sugar suppresses uptake. For certain metals (e.g. zinc and iron) alcohol suppresses uptake while for others (e.g. copper) uptake is enhanced. The extent of metal leaching depends on the type of metal and brand of brew, and assumes serious proportions with some metals including zinc. Leaching efficiency of metals by local brew brands is ranked thus: zinc > iron > copper. Examination of local brews laden with copper has shown depletion of copper levels by between 75% - 100% of initial levels upon handling in a galvanised steel container. The potential application of this observation is discussed.