The possibility of using sugar‐beet molasses as the sole carbon source by different strains of Xanthomonas was evaluated in terms of xanthan gum production. Highest yield of xanthan was obtained at a 50 g/kg sucrose concentration in a medium based on sugar‐beet molasses by the wild‐type isolate Xanthomonas campestris pv. campestris (19.8 g/L) (P < 0.05). The apparent viscosity of the xanthan produced by wild‐type isolates were compared with the commercially used gum in a mayonnaise product. No difference was shown. It seems that less expensive substrates could be a suitable and cost‐effective alternative for xanthan gum production. PRACTICAL APPLICATIONS Molasses is a co‐product of sugar production, both from sugar beet as well as from sugar cane, and is defined as the runoff syrup from the final stage of crystallization, from which further crystallization of sugar is uneconomical. Since this industrial by product constitutes valuable source of growth substances it is widely used as a substrate in microbial fermentations. Xanthan gum is a water‐soluble hetero‐polysaccharide that is produced industrially from sucrose or glucose by fermentation using the gram‐negative bacterium X. campestris. Commercially available xanthan gum is relatively expensive due to glucose or sucrose being used as the sole carbon source and the very stringent purity standards of the Food and Drug Administration for foods. Based on a preliminary analysis, the use of sugar beet molasses for xanthan gum production has the potential to be a cost‐effective supplemental substrate specially when non food grade gum is to be produced.

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