Flavour development during beef stock reduction

In beef stock, made of brisket, water and NaCl, reduction time was found to play a major role in development of volatile compounds and sensory characteristics. Nine stock reductions, made by varying concentration factor and reduction time (controlling power input from stove), were compared using dynamic headspace gas chromatography and a descriptive sensory analysis (n = 9). Aroma compounds could be classified into 5–6 groups, based on their concentration–time profiles. The initial flavour was found to be lost for both slow and fast reductions but, for fast reduction, insufficient time was left for development of new flavours. The decrease in volume alone, as often referred to in recipes, is accordingly not sufficient as the sole indication of flavour development. The observed changes in sensory properties, and changes in the underlying concentrations of chemical compounds during reduction, are discussed with regard to theoretical considerations about evaporation of volatile aroma compounds from the boiling two-phase (oil–water) liquid and heat-induced chemical reactions.