Crack formation in chocolate pralines

Abstract: Chocolate pralines are complex food products that contain a soft filling surrounded by achocolate shell. One problem with pralines is that the filling often starts to migrate throughthe shell which causes major structural changes that, for water or liquor based fillings, couldresult in cracking of the shell. Cracking is one of the major issues that lead to reduced shelflife in chocolate pralines. The main suggestions for crack formation are that cracks form dueto moisture or ethanol migration through the chocolate shell, or due to an unbalanceddistribution of moisture in the filling that causes some parts to shrink and other to expand.In this work, two praline geometries and four different model fillings (with water activities(aw) between 0.67 and 0.99) were analysed with respect to chocolate shell cracking duringstorage. The pralines were stored for 28 days, during which high resolution images of thepralines were collected and analysed by a digital colour imaging system. Furthermore, wateractivity measurements in the shell, combined with weight changes in the pralines gaveinformation on migration properties during storage.The results showed that pralines with aw 0.99 in the model filling cracked first and to thehighest percentage for both geometries. Pralines with model filling aw 0.86 and aw 0.78 hadquite similar results to each other, and cracked to a considerably lower percentage thanpralines with model filling aw 0.99. For model filling aw 0.67, square pralines did not crack atall while round pralines cracked at a low percentage. Round pralines started to crack first forall model fillings during the storage period.The major conclusions that can be drawn from this work are that both water activity (aw) inthe model filling and praline geometry have an impact on crack formation in chocolatepralines.