Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from PDF version of thesis.Includes bibliographical references (p. 113-117).Carbonated frozen foods are not common on the market due to the limited liquid water available to dissolve CO₂ . CO₂ clathrate hydrates can change this because CO₂ is trapped in crystalline water. The CO₂ flash-freezing process developed in this thesis forms CO₂ hydrates directly in a confection as it freezes. In this process, the confection mixture is dispersed in liquid CO₂; then the combined fluids are flashed to 10-20 bars. The mixture breaks up into small fragments, which rapidly crystallize into CO₂ hydrate (instead of ice) due to the intimate contact between mixture and evaporating CO₂ . This CO₂ hydrate formation results in a frozen, carbonated confection. CO₂ hydrates have a significant impact on packaging and storage requirements for the confection. This study shows that the minimum storage pressure is determined by the ice- CO₂ hydrate-gas equilibrium (IHG) curve, which does not change with the concentration of solutes in the aqueous phase. The minimum CO₂ content in a storage vessel is determined by the amount of CO₂ needed to avoid ice; in the presence of ice CO₂ can redistribute quickly, leading to an inhomogeneous product. Packaging must therefore be designed considering the significant CO₂ evolution from dissociating CO₂ hydrates during heat shock. Warming of a confection causes CO₂ hydrates to dissociate, even at pressures greater than the IHG pressure due to the requirement of chemical equilibrium between water in aqueous and crystalline phases. In packaging with limited heads pace, this CO₂ release increases the pressure significantly.(cont.) When CO₂ hydrate confections are consumed CO₂ is strongly perceived both through tingling caused by carbonic acid and through tactile stimulation caused by bubbles. A higher concentration of CO 2 is required in CO₂ hydrate confections than in carbonated beverages for similar fizziness perception because a significant fraction of the CO₂ escapes when a consumer exhales. The CO₂ concentration in the melted confection does not exceed the solubility of CO₂ at atmospheric pressure, but ingredients in the recipe can modulate the growth of bubbles as the confection melts. Consumer testing is needed to define the form and style of CO₂ hydrate confection that should be pursued.by Teresa Baker Peters.Ph.D
