Superheated Ice

About

Researchers at Swansea University have developed a novel method for manufacturing aerated semi-frozen products such as ice cream. Negative pressures and sub-zero temperatures are used to suspend a water mixture in a so-called double metastable state. Nucleation of gas bubbles throughout the mixture is initiated by an impulse force, resulting in a freshly prepared aerated semi-frozen product. The technology is patented and is being offered for exclusive or non-exclusive licence. Technology When pure water is cooled below the freezing temperature it will not become solid immediately, but rather stay liquid in a so-called metastable condition. However, as soon as a solid nucleus forms due to random fluctuations or a disturbance from outside, large enough to initiate the freezing event, the whole system will rapidly transform into ice. The underlying theory of such liquid-solid transitions is well known and documented. The Swansea invention extends this concept by forcing a water based product into a doubly metastable condition. In this state the sample wants to simultaneously vaporise (as it is under negative pressure) and freeze (as it is below freezing temperature). When a bubble nucleates and expands the surface of the bubble cools further, freezing instantaneously. This creates a surface for further bubble nucleation, the process cascades and the entire sample freezes instantly with micro bubbles (diameter <1um) entrapped. The net effect is the instantaneous transformation of a simultaneously supercooled and superheated liquid into an aerated semi-frozen product. Achieved without mechanical beating, this process is simpler and faster than conventional ice cream production techniques. Furthermore, because it does not involve mechanical beating, energy consumption and clean up costs are reduced. Applications Ice cream is manufactured using processes virtually unchanged since Agnes Marshall invented her ice cream machine in the 1890s. Air bubbles are introduced mechanically by scraping the ice cream mixture against the walls of a frozen container. Depending on blade speed and temperature, air cavities are typically >50um. Unfortunately this is a time consuming and energy intensive process, whilst product quality and “mouth feel” are affected by the size and distribution of micro cavities and storage conditions before consumption. The Swansea invention presents a radically new method for producing aerated semi-frozen foods such as ice creams, water ices, sorbets and sherbets. Since aeration is achieved without beating, the energy consumption is less than conventional methods whilst product texture is enhanced. Furthermore, since the product can be manufactured instantly, it is amenable to shipment and storage in liquid rather than aerated frozen form. This has the potential to transform the way ice cream is stored and distributed, opening up new markets where inadequate cold storage and logistics preclude the sale of frozen confections.