Age group determines the acceptability of protein derived off-flavour

•Heat-treatment of protein ingredients can impart sulfurous flavours into beverages.•Sulfurous flavours negatively impacted consumer acceptance of a dairy beverage.•Older adults had greater acceptance of sulfurous flavours compared to younger adults.•Diacetyl reduced the negative impact of these compounds for both age groups.•Best estimate thresholds give a conservative estimate of off-flavour acceptability.