Aeration and rheology of buttercream icings

WALTON, H; CALVER, K; ORONA, JD; FERNANDES, RR; MEZA, BE; PERALTA, JM; WILSON, DI; ZORRILLA, SE

Auckland

Congreso; Chemeca 2023; 2023

Institution of Chemical Engineers

Aerated icings, also called buttercreams or frostings, are a fat-rich, sweet, and uncooked type of glaze materials made by mixing powdered sugar and fat (e.g. butter, vegetable oil shortening) together to form a bubbly fluid. Aerated icings are usually used to coat baked products and desserts for decorative, flavouring, and protective purposes. An ideal aerated icing will exhibit viscoplastic behaviour, flowing when the imposed stresses exceed a critical (yield) stress. The final appearance and shape of the product is intrinsically associated with this critical stress, which should be large enough to overcome gravitational and surface tension effects, avoiding slumping or other loss of shape. Much of the research on bubbly liquid rheology has focused on systems with a Newtonian continuous phase. In aerated icings the continuous phase is non-Newtonian, with at least three phases – in this work, particulate sugar and an emulsion (butter). The continuous phase is marked by a relatively high critical stress, making it difficult to characterise in standard rotational rheometers. Aerated icings were generated in a planetary mixer and the air volume fraction, , followed a simple growth kinetic with little long term decay exhibited in creams. Optical microscopy and X-ray microtomography indicated that most of the air was entrained as small (~ 10 µm diameter) bubbles but some larger voids were also present. Methods developed for dense suspensions (pastes) were used to quantify the yielding, flow, and creep behaviour of the materials, and to determine how these depend on . Vane tool testing was used to quantify static critical stresses for yielding, and showed a strong dependency on . Lubricated upsetting (constant volume compression) proved to be superior to squeeze flow testing for determining the extensional viscosity, and the data were fitted to the Herschel-Bulkley for Pastes model (Mascia and Wilson, 2008, J. Rheol., 52(4), 981-998).The results are presented in terms of a framework for understanding the impact of processing and formulation on the properties of complex food fluids.