The Space Between: Reverse-engineering Bread

After our first five blogs, being highly focused on materials science and engineering, we are taking this time before Thanksgiving (apologies to all living outside of the US who read this) to write about an important foam that is traditionally part of the Thanksgiving dinner. That foam, of course, is bread. This blog is about the difficulties encountered in recreating a delicious foam, see Fig. 1, even when the exact ingredients are known. As materials scientists and engineers read this we hope you will see analogies to your own materials studies. For the bakers, both professional and amateur, we have a link after the bread story that will “translate” it from baking to materials terminology. We hope you enjoy!

Figure 1 A close-up photograph of bread showing the pore structure.Note the variation in pore structure at the various locations.

In 2013, when we first set out to write our book, Voids in materials: From unavoidable defects to designed cellular materials, one of us (GMG) travelled a lot, mostly by airplane. Frequently, he had conversations with the passenger sitting next to him. Sometimes it was a simple “hello, where are you travelling?” Other times it was the small talk “how’s the weather?” type of conversation. On the rare occasions he encountered a real “storyteller.” And he means this in the most positive way possible – there was an intent listening during the conversation, a desire to understand, etc. When he was lucky enough to sit next to a storyteller, our book would undoubtedly come up. He would give the short, four-sentence description and without fail a storyteller would relate to it. It got to the point that he could identify a storyteller after a few minutes of discussion and once the void book was brought up, he would ask – “what is your void story?” Over time, this question was asked to physicians, optometrists, chefs, and dancers, just to name a few.

The void story that GMG would like to relate is from a woman whose first career was as a professional bread baker. She had many other careers, baker, writer, translator, and was currently getting second Master’s degree from Queens College in New York in the Performing Arts. What follows is GMG’s account of her story, kind of a baker’s version of a materials scientist and engineer developing a foam:

The story starts with her as a child growing up in Florence, Italy. She lived there until she was 6 or 7 and they then moved to the US. Years went by and during her professional bread baking career, she moved back to Florence. She was walking through the streets where she grew up and she happened to walk by a restaurant that took her back to her childhood in Florence. It was the smell of bread in the air that took her back. She remembered sitting outdoors with her family, having lunch, while smelling and eating this bread. As a child she loved it and now, as a professional baker, she was pulled toward the restaurant to sit, have lunch and eat the heavenly bread. Would the bread taste as good now as it did when she was a child?

The bread was as good as she remembered and she went on a quest to recreate it, sort of a challenge. She studied the bread; the crust, the size of the holes, how the size of the holes changed as it approached the crust, the texture, how it felt when she ripped it apart, how it felt when she took a bite.

With all this information she went back to her kitchen to recreate the bread. During this first round of baking she was not very successful. She tried every combination of yeasts, salt, sugar, flour, and water that she could think of, but no luck. She decided to go back to the restaurant, explain to the server her story and ask to speak to the baker. The server brought out an old man in his 80s. He had been baking the bread since the time of her childhood.

The old bread baker quizzed her about the yeast, flour, and all of the other ingredients. He mentioned that she needed to use #1 baking flour. She had never baked breads with this type of flour and had no idea where to get it in Florence. The old baker told her to…. “go down this road, turn left…find the blue door, knock 3 time and tell the guy that answers the door that I sent you.” With this information she went on her way for another round of making bread.

This time using the #1 flour, with successive attempts, she was getting closer and closer to the old, taste, texture and the hole pattern. Finally she decided to make a few loaves and just take it to the old baker and ask him about the final tweaks to the ingredients to make it exactly the same. The following day she sat down with him and broke open the bread loaves. He studied the holes and how their size changed closer to the crust and larger in the center. He squeezed it in his hands and felt the resistance and how it bounced back after squeezing. He put the bread in his mouth, noting the texture and taste. He looked pleased. The old baker then asked her about the oven she used. Being a professional baker, it was a high-end professional home oven. The old bakers then said “come with me.” He took her to his kitchen where there was a 10-foot clay, wood-fired oven that he built himself. He told her, with the oven she had at home, the bread she brought that day was as close as she would ever get. The old baker’s wood- fired, clay oven was the missing ingredient.

To us, there are excellent analogies in this quest to recreate a loaf of bread and the design of materials, in this case a foam, that materials scientists and engineers do regularly. This quest reflects the interdependence of material chemistry, structure, properties and performance; see Fig. 2 (Liu, Chen et al. 2003).

Figure 2 A schematic illustrating interdependence of key factors in materials science and engineering (Liu, Chen et al. 2003). These dependencies have analogies in many disciplines such as baking.

In this case the chemistry was the ingredients; flour, salt, sugar, water, etc. The processing was done in a home-made clay, wood fired oven v. an expensive professional grade home oven. The homemade oven was built specifically to make bread while the home oven is a more flexible “processing unit” that can cook the bread, turkey, sweet potatoes and pumpkin pie for your Thanksgiving dinner!

We hope this story illustrates that The Space Between materials science and engineering and baking is not all that large. As in baking, there are a lot of intangibles that science and technology cannot replicate when making a material. Although we try to control every aspect of production, whether it is bread or polyurethane foam, duplication is always difficult. Factors such as ambient temperature, relative humidity, and elevation all can factor into product quality. Materials manufacturers deal with this issue all the time when manufacturing the same product in different parts of the world. However, many times it is this intangible that leads to the finest quality product (think of the old baker’s oven that he made himself). It can come down to one person; the operator, the baker, the quality technician, the grandmother, putting that special touch into the product or process to make it perfect.

In our book we highlight various way of introducing voids into materials such as the “chemical blowing agent” i.e. (leavening agents) and aeration, which are extensively used in the food industry. The chocolate bar in Fig. 3, taken from our book, Voids in Materials, illustrates a wide cell size distribution that can occur during aeration. Furthermore, in the early 2000s, the food industry started adopting the processes and characterization methods that had been established earlier for polymer-based foams. As in engineered foams, the microstructure is impor­tant in controlling the mechanical properties, texture, and esthetics in the foods (Lim, Barigou 2004).

Void structure, size, shape, and distribution are important to ensure consis­tency of foods like ice cream, soufflé, sponge cakes, chocolate bars, marshmal­lows, biscuits, and breads. Lim and Barigou (Lim, Barigou 2004) used X-ray micro-computed tomography, a technique that is common in engineered foams, to characterize the cell structure of many cellular foods. Figure 4 illustrates the wide cell size and shape distributions caused via the aeration process.

Figure 3. A chocolate bar, in which the center filling has been aerated. Note the large distribution of cell sizes.

Figure 4 X-ray micro-computer tomography section showing the pore structure of various aerated foods. (a) Mousse, (b) marshmallow, and (c) chocolate (Lim, Barigou 2004). Note the size and shape difference of voids within a single material.

Translation

As the story moved along, the integral skin foam was as good as she remembered and she went on a quest to reverse engineer it. In her mind it was a challenge. She studied the integral skin foam; the skin, the pore size and size distribution, how the pore size changed as it approached the skin, the texture, tear strength, the stress-strain response when it was compressed.

With these data she went back to her laboratory to reverse engineer this integral skin foam. During this first round of formulation she was not very successful. She tried every combination of chemical blowing agent, catalyst, polymer and diluent that she could think of, but no luck. She decided to go back to the university, explain her story and ask to speak to the foams expert. The expert was a professor that turned out to be in his 80s. He had designed the foams many years before, back when she was a child.

The professor quizzed her about chemical blowing agent, catalyst, polymer and diluent and all of the other raw materials. He mentioned that she needed to use a higher molecular weight polymer. She has never made integral skin foams with this polymer and had no idea where to get it. The professor told her to…. “go to Supplier B and ask for polymer XY.” With this she went on her way for the second round of formulations.

This time using the higher molecular weight polymer, with successive attempts, she was getting closer and closer to the professor’s compressive properties, texture, porosity size and size distribution. Finally she decided to make a few samples and just take it to the professor and ask him about the final tweaks to the formulation to make it exactly the same. The following day she sat down with him and sectioned the integral skin foam into standard test specimens, he measured the free-rise density and the porosity size and size distribution and how it changed closer to the skin and larger in the center. He performed compression tests, collecting stress/strain as well as compression-set data. He looked pleased. The professor then asked her about the oven she used. Having a well-equipped laboratory, it was a high-end programmable oven. The professor then said, “come with me.” He took her to his lab where there was a customized oven designed specifically for making this integral skin foam. He told her with the high-end utility oven in her lab, the foam she brought that day is as close as she will get to his original foam.

source: http://scitechconnect.elsevier.com/the-space-between-reversing-engineering-bread/?utm_source=socialmedia&utm_medium=Materials&utm_campaign=The+Space+Between%3A+Reverse-engineering+Bread&sf5983276=1#1