RESUMEN
Acid whey is a by-product from cheese processing that can be employed in beverage formulations due to its high nutritional quality. The objective of the present work was to study the physicochemical characterisation of acid whey from Petit Suisse-type cheese production and use this by-product in the formulation of fermented milk, substituting water. In addition, a reduction in the fermentation period was tested. Both the final product and the acid whey were analysed considering physicochemical determinations, and the fermented milk was evaluated by means of sensory analysis, including multiple comparison and acceptance tests, as well as purchase intention. The results of the physicochemical analyses showed that whey which was produced during both winter and summer presented higher values of protein (1.22 and 0.97 %, w/v, respectively), but there were no differences in lactose content. During the autumn, the highest solid extract was found in whey (6.00 %, w/v), with larger amounts of lactose (4.73 %, w/v) and ash (0.83 %, w/v). When analysing the fermented milk produced with added acid whey, the acceptance test resulted in 90 % of acceptance; the purchase intention showed that 54 % of the consumers would 'certainly buy' and 38 % would 'probably buy' the product. Using acid whey in a fermented milk formulation was technically viable, allowing by-product value aggregation, avoiding discharge, lowering water consumption and shortening the fermentation period.