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The flow behavior, pH and the main microbial populations of kefir, produced from commercial pasteurized and homogenized bovine milk with fat contents of 0, 1.5 or 3.5% (w/w) and the addition of 1, 3 or 7% (w/w) of kefir grains, were examined after storage for 0, 7 and 14 days at 4C. Increasing the kefir grain inoculum or the storage time of the final product resulted in pH reduction. The viscosity of kefir increased as the fat content of the milk increased, whereas it was reduced during storage for 14 days. Samples prepared with 7% kefir grains exhibited greater viscosity values when compared with samples prepared with 1 and 3%. The increase of kefir grain content resulted in a reduction of lactococci and an increase of yeasts, whereas increasing storage time of kefir resulted in population reduction for lactococci and lactobacilli and to an increase of yeasts. PRACTICAL APPLICATIONS Kefir is a dairy product with noticeable nutritional and health‐related attributes increasing its market potential in today's health‐oriented food market. The quality of the product, its standardization and the parameters affecting it is of scientific and commercial interest. The present study investigates the effect of milk fat content, kefir grain inoculum and storage time on the microbial populations, the pH and especially the rheological properties of the product. A prototype pneumatic tube rheometer was used for the study of the rheological properties of kefir and their development during fermentation and storage.

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