Whey was fermented using different lactic acid bacteria in order to obtain an ingredient as a substitute for butter in pastry products. Lactococcus lactis subsp. lactis biovar diacetylactis was selected based on its capacity to produce buttery flavours like diacetyl. Fermentation parameters such as temperature, aeration, citrate addition, and the duration of each fermentation step were selected in order to boost diacetyl production. Fermented whey was then added as an ingredient to white sandwich bread which did not initially contain any butter in the recipe. Sensory analysis brought to light that the buttery aroma was under the perception threshold in the bread containing the mixture even though the fermented whey contained diacetyl.