Fermentation of worts with high concentrations of fermentable sugars has become common practice in large clear beer breweries that use high gravity worts containing 16-18% (w/v) dissolved solids to obtain high alcohol contents. Normal and high gravity worts, ranging from 12 to 20% (w/v) initial dissolved solid contents were used in industrial opaque beer brewing and the biochemical characteristics of the brews were determined. Characteristics of the beers varied according to wort gravity. Decreases in dissolved solids and maltose contents were recorded during fermentation for all the brews. Higher residual dissolved solids, ranging from 6.5 to 11% (w/v), were recorded for the high gravity brews as compared to the normal brews, which had 3.5% (w/v) residual dissolved solids. An increase in ethanol levels was recorded during alcoholic fermentation for all the brews and the maximum ethanol levels, recorded after 72 h of fermentation for all the brews, were 3.5 and 6.0% (v/v) for the normal and high gravity beers, respectively. The optimal wort dissolved solids content recorded with regard to ethanol productivity was 18% (w/v). Increases in lactic acid and acetic acid levels were recorded for the brews, reaching maximum levels of 2.25 and 0.48 g/L, respectively, after 96 h of fermentation. No propionic acid was detected in any of the brews. Considering the quality of the beer, there was no settling observed for all the beers at 48 h of aging. Viscosity values, ranging from 100 to 190 mPa.s were higher than the expected levels for the industrial opaque beer (60-80 mPa.s) and values recorded for head were within the expected range for the industrial opaque beer (3 to 4).
Key words: High gravity, opaque beer, dissolved solids, ethanol.