A beverage nucleator system for a supercooled beverage container may include a frame for receiving a beverage container and an ultrasonic transmitter positioned therein. A convex protrusion from the ultrasonic transmitter ensures good contact and therefore good transfer of ultrasonic energy through a top surface of a closure of the beverage container, even if the beverage container is positioned within the frame at an angle to the ultrasonic transmitter. Alternatively or additionally, a packaging holder comprising a plurality of supports may be provided to ensure that the top surface of the closure is parallel with the ultrasonic transmitter.