B Corp certification is considered a viable instrument to support small and medium-sized enterprises (SMEs) in adopting sustainable practices. However, there is a lack of evidence to what extent this instrument can anchor sustainability at the core of SMEs. This study investigates the B Corp certification process of a SME, a craft brewery in southern Sweden, regarding the extent to which it helped infusing sustainability into the business’ mission, practices, corporate form, certificates, and capacities. Results show that the B Impact Assessment, as part of the certification process, positively influenced the business’ mission, practices, and capacities. Limited influence on social commitment and adoption of a sustainable corporate form can be explained through regulatory context and time required for deep organizational change. To enhance the effectiveness of B Corp certification, we recommend making it even more adaptable to different geographical and social contexts and increase focus on impact business models.