Porous media characterization of breads baked using novel heating modes

The nature of pore spaces in breads baked using various heating modes (microwave–infrared (MIR), microwave–jet impingement (MJET) and jet impingement (JET)) were characterized in terms of total porosity, fraction of closed, blind and flow-through pores, and pore size distributions using several novel and old techniques (liquid extrusion porosimetry, scanned image analysis, pycnometry, volume displacement method and scanning electron microscopy or SEM). For the breads studies here, a very significant pore size distribution exists covering diameters of a few microns to several thousand microns. It appears that the pore size distribution is bimodal and only a combination of techniques can provide comprehensive information, i.e., any one technique cannot cover the large range of pore size, total porosity and flow-through vs. closed pores. A significant fraction of the pores was found to be closed. Breads baked in JET had the highest total porosity followed by MJET and MIR. Other measurements on breads baked in JET also lay on one end of the spectrum (either smallest or largest), which is consistent with SEM pictures where JET baked breads looked quite different from the ones baked in other ovens.