Quantitative MRI study of layers and bubbles in Danish pastry during the proving process

Abstract

Proving of a real sized Danish pastry (10 cm × 5 cm) was studied by MRI to visualize dough and fat layers and their evolution. The number of fat layers was varied from 4 to 12, the latter being relevant to the lower range used on an industrial scale. A new method of quantification of the three components, gas, gas-free dough and fat, in partial volume was applied to MRI images of Danish pastry during proving. The method estimated accurately the proportion of gas with a maximal bias of 5%. Sheeting steps up to 3 did not modify the inflation process of pastry and hence did not alter the gluten network and its capacity to retain gases at the global scale. A degassing effect of lamination was observed from the third sheeting step (dough layers with median thickness of about 750 μm). Thickness between dough layers was not the same from the bottom to the top of the laminated dough and this was amplified during proving. However, the gas proportion in these layers was homogenous and there was no effect of the position of the layer on its expansion. Large bubbles (> 0.5 mm) were visualized in dough layers but they were not elongated at this step of processing, as are bubbles typical of Danish pastry once baked. Eye-shaped bubbles were instead visualized in fat layers; their number increased more rapidly than that of fat layers. They contributed to less than 10% of overall inflation. Finally, large, undetectable portions of fat (40 ± 13 mm equivalent to about 80 pixels) were assigned to missing fat material and breaks in the layering, considered as undesirable by the bakers. These void spaces represented 7.7% of the expected total length of fat layers in the MRI images, a proportion also reported from CLSM images of the same pastries.