Abstract: An semi-solid mixture, such as a particulate meat mixture, is brought into contact with a vibrating surface, whereby energy is transported across the surface into the mixture. The vibration is generally contemplated to be in the ultrasonic frequency range, and the energy injection is contemplated to be sufficient to cause local physical and chemical changes in mixtures susceptible to such changes, and generally to cause changes in the direction of increased tensile strength and resistance to flow. In general a skin is formed on the mixture, and with greater processing efficiency then if such skin were formed by purely thermal means.