Secret inside the delicious croissant

What makes a delicious croissant and fluffy cotton? Save the secret, Braulio Macias Rodriquez and Alejandro Marangoni at Guelph University in Ontario, Canada, did not expect their research to contribute to the opening of new topics in material science.

Croissants are layered according to the characteristics of specialized fats used for baking.(a) Special fats are deformed differently than multi-purpose fats.The diagram demonstrates the internal forces (tension force is the force per unit area) growing cyclically (tension force is the amplitude of the relative size increase) at a corner frequency (also called is the angular speed) of 3.6 radians per second.The tension in multipurpose fats gradually increases markedly and a sudden drop indicates that the internal structure is broken.(b) In many fats, triglyceride molecules crystallize into thin plates at the nanoscale as shown in this electronic microphotograph.Thin sheets represent the smallest level of three structural layers in a dedicated fat.(c) Electronic microphotographs a characteristic of the largest structure of fat, a crystal network at the micro level, which can add liquid oil.

It can be seen that there is no need for too many ingredients to make croissants, just a little dough - mainly wheat flour and water, with a little fat, usually butter. If making bread on an industrial scale, the dough and butter layers only 1 cm thick are stacked or the fat is put in between the dough layers. Kneading dough to create alternating layers of flour and fat at a thickness of 100-200 µm, thereby giving the cake shape and porous texture we often see: when baking, water evaporates as layers of powder bulging and stretching like balls.

Flow and deformation of fat

The rheological properties of fat - in other words, the flow and deformation of fat , is an important factor in making a delicious croissant. Fat must have a certain hardness: if it is too hard, it may not be possible to laminate the powder, even break it, and if it is too soft, the powder will absorb the fat.

So using unsuitable fat will make the cake not blooming and easy to break. Fortunately, the baker and scientist realized that not all fats are suitable for all types of foods. So they developed 'specialized' fats for special purposes.

An example is finding a fat suitable for stuffing biscuits. The best croissants are made with butter but sometimes when the price of butter increases or some temperature problems, one must replace it with another type of fat. The bakers know that, in order to handle the dough with butter successfully, the room temperature should only fluctuate in a small range - from 15 to 20 ^degrees Celsius, and the floating dough can help dough in the wider temperature range.

In the lab, Braulio Macias Rodriquez and Alejandro Marangoni studied flour-made croissants. They found that different fats give different properties.

The rheology in fat helps create an underlying colloidal network of fat crystals. Formed by the crystallization and format of fat, this network has a multidisciplinary structure. To successfully roll the dough, it must 'keep an eye out' for the crystallization process: the fat needs to be cooled, molded to create many tiny crystals and form a lattice.

The baker assesses the fat with the eyes and the feel of the fingers. Scientists have a better way of doing deformed fat, such as periodic oscillation, and expressing their states in a stress (internal forces arise on each a unit of area in a deformed object) with a link extension, such as the following table a:

In this case, the approach applied by the researchers is to create a diagram with a large amplitude oscillatory shear (LAOS) technique - itself a new research topic. LAOS can be applied in all cases to investigate the structure and function of different materials, including polymers, glues and foods because it has the ability to decay an oscillating response of an object. material into elastic properties.

As the table shows, because the strain is very small, the stress of both specialized and multi-purpose fats has a linear response. Fats act as solids with viscosity and deformation; In fact, it is possible to detect the ability to behave like a solid of fat when observing its frequency spectrum.

This linear state is very small and ends at 0.01% tension - the critical value of materials within a narrow range or van der Waals interactions. When beyond the critical value, these tensile forces are sufficient to break the crystal net and bring it into a non-reversible elastic state. Therefore specialized fat must withstand the pressure to be easily transferred to the nonlinear state during lamination.

Through their LAOS experiments, two types of fats are capable of producing the highest tension at the same level - or elastic tension in the range of 4000 - 5000 Pa. But their plastic flow behaviors are completely different: when deformation, tension of specialized fat is stable and tension in multipurpose fat abruptly decreases, indicating internal breakage; Therefore, multipurpose fat cannot help to thin the dough well.

Multi-scale structure

The rheology of fat increases from the hierarchical self-aligning structure, which combines layers according to the physical length in the range of a few angstroms to tens of micrometers. At the molecular level, fats are formed from triglyceride molecules (TG), in which fatty acid triplets emanate from the glyceryl spindle. Because of our love of croissants, we may not be interested in the fact that specialized fats may contain a lot of metabolic acid, if too much is allowed, it can lead to heart disease.

Croissants.

Therefore, one of Braulio Macias Rodriquez and Alejandro Marangoni's goals is to find other, healthier fats but also be able to make delicious, fluffy cakes to replace specialized fats. use.

X-ray scattering experiments have distinguished three levels of structure in specialized fats, since it is reflected in non-Newtonian (power-law) states - the dynamics of substances with viscosity obey Newton's law, evident in a graph of small super-angle scattering intensity with scattering angle. The structure at the first level consists of thin plates at nanoscale, TG crystals. These specialized fat crystals are not only smaller than multipurpose fat crystals but also softer in the border between them.

The second-level structure consists of crystalline, cylindrical blocks and has the ratio of height - small diameter, naturally clinging together to form clusters at the micro and super-micro dimensions. It is these additional techniques that create the third structural level, an extremely small crystal net that covers liquid oil. Electron microscopy techniques show that crystal clusters in specialized fats are arranged into a sequential layered network (see figure c) and conventional fats do not have a dislocation this self.

Different levels of internal length in a structural order of a fat have important implications for how energy is consumed as we see it in rheology. In natural materials and biological materials, the linkage between different lengths can lead to orderly tolerances in alignment with a very small structure that allows for high stress consumption. If not, it will lead to damage to the material.

Indeed, specialized fats with a three-level structure consume 10 times more energy than multipurpose fat. The stress dissipation in the fat and the response of the micro structure in the nonlinear deformation state are still topics that need further investigation. An interesting problem is that there is one more feature of specialized fats: the slip of these crystalline layers can affect the energy consumption and porosity of croissants.