The leavening activity of kefir grains in lean dough and their efficiency in producing bread of good quality, in terms of loaf volume, flavour, texture and shelf life, were evaluated. Although the leavening rate of commercial baker's yeast was higher (30 ml/h), kefir performed well (24 ml/h), and produced bread of good quality, resembling traditional sourdough bread. Rising was satisfactory (specific loaf volume 3.0-3.3 ml/g) and breads produced with kefir retained more moisture, had a firmer texture, lower acidity (pH 4.9-5.5) and retained their freshness for longer compared to baker's yeast bread. Consumers showed a preference for kefir-leavened bread, although a preliminary headspace GC-MS analysis of volatiles did not reveal significant differences between the two types of bread. (c) 2004 Elsevier Ltd. All rights reserved.