It is said that bread-making is an art. Indeed, bread is the subject of popular still life paintings drawn by artists like Vincent van Gogh and Monet. It is a dearly loved, staple food item in most people’s diets, so even a picture of a loaf of bread can remind us of the pleasure of biting into a crunchy crust to find a soft crumb and the enjoyable flavour of fresh bread.

On the face of it, making bread is simple. Mix some flour with water, salt, sugar and yeast, let the dough rise and then bake. So, why is bread making an art? There are a number of reasons. The selection of flour is important; until bread is baked, it is hard to know how well the flour will work. Bakers have found from experience that how the dough is mixed, shaped and baked affect the quality of the baked products. Thus, the skills of the individual baker are important. Even in industrial productions, human intervention is common as doughs are often mixed to “baker’s feel” and downstream processes adjusted accordingly.

Breads are porous materials. Some consumers prefer crumbs that have large holes while others prefer small holes. How the pore structure affects appearance and texture of crumbs is not well understood. It was reported by Baker (1939) that breads were permeable to air and that low permeability breads had a brittle texture. Thus, pores affect mechanical characteristics of breads. But little more is known.

A simple analysis of the baking process tells us that breads must contain open cells. During proofing, carbon dioxide, produced by yeast, migrates to air bubbles present in doughs and the dough expands. Further expansion of pores takes place in the oven when the starch gelatinizes imparting solidity to the structure. The bubbles burst which stabilises the expanded structure with respect to atmospheric pressure. If the bubbles did not burst, the bread would collapse when taken out of the oven. Thus, it stands to reason that some bubbles interconnect form open cells, but further details, like how the internal structure looks or how it affects softness, chewiness and other textural qualities of bread remain unknown.

The role of pores governing the permeability of rocks is well studied in the Geosciences. The size and distribution of open pores determine the permeability of rocks, which ultimately affects the production of oil and gas from a well. A new area within Geosciences is digital rock technology. The two mainstays of this technology are computerised X-ray micro-tomography (micro-CT) and computer simulation of fluid flow in digital rocks, re-constructed using the 3D scans of pore structures (Jie et al. 2009). Investigating the effects of pore structure using ‘digital’ rocks provides ideas for innovative technologies for oil and gas production.

We followed the methodologies established for rocks to visualize the pores in a range of sandwich breads in 3D. We reconstructed images to obtain 3D maps of pores with estimation of pore volumes, which showed that breads were almost 80% porous and 99% of pores were interconnected. Thus, breads are made of a single, massively interconnected, open cell. However, closed cells are also present. The size and distribution of closed cells affect the stress-strain plots of crumbs, measured from true strain rate compression tests (Wang et al, 2011, Youtube clip).
A key learning from this study has been the realization of the importance of closed pores in affecting the pliability of breads. On bending a slice of bread, the path of fracture propagation is long as the cells are extensively interconnected in bread. This means the bent portion of slice does not break off; it needs to be torn off. However, with a larger number of closed pores, the path for fracture propagation is shorter as in cakes, which are crumbly.

To date, there is no known method by which texture of bread can be controlled to produce prescribed pore structures. So, we constructed digital breads using experimental data for pore sizes. Visually, the ‘look’ of the virtual bread crumbs was similar to that of real bread. We also investigated the ‘feel’ of bread by performing ‘virtual’ compression tests assuming a linear elastic model for the solid phase of the digital bread. Results showed that for a given porosity, a 50% decrease in the average closed pore volume of the experimental data could soften the bread by 25% (Wang et al. 2013).

Moving on, we are analysing pore structures in doughs to gain a more comprehensive understanding of how flours affect the expansion of pores during proofing as that’s when the distinction of closed pores in breads are most likely set.

Overall, the technique of developing digital breads and doughs could lead to low cost alternatives to understand flour selection for making breads and widen the choice of flours to make breads. It is conceivable that bread-making will not remain as much an art as it is now!


Baker, J.C., (1939). “The permeability of bread by air”, Cereal Chemistry 16, 730 – 733.
Liu, J., Regenauer-Lieb, K., Hines, C., Liu, K., Gaede, O., Squelch, A., (2009), “Improved estimates of percolation and anisotropic permeability from 3-D X-ray micro- tomography using stochastic analyses and visualization”, Geochemistry Geophysics Geosystems 10 (5)
Wang. S. , Austin P. And Chakrabarti-Bell, S., (2011), “It’s a maze: The pore structure of bread crumbs”, J of Cer. Sci., 54, 203-210 (doi:10.1016/jcs.2011.05.004)
Wang, S., Karrech, A., Regenauer-Lieb, K. and Chakrabarti-Bell, S., (2013), Digital bread crumb: Creation and application, J Food Engr., 116 852 – 861 Analyzing and Quantifying the Pore Structure of Baked Products, (