Basic Theoretical Concepts
Stirring and mixing are complex homogenization operations involving hydrodynamic (discharge regime), thermal (transfers), chemical (reaction) and mechanical (shearing) phenomena. These operations, when carried out industrially, require the implementation of efficient mixing systems to ensure the stability and the consistency of the mixtures at low costs (minimal time and energy). It is within this context that blenders by mechanical rotation were imposed in many industries for all kinds of mixtures:
Special Case of the mixture of high viscosity fluids
The aim being not to only mix several ingredients, but also to texture the final product (alignment of fibers) The mixture of these materials is often done under laminar or transition regimes. There is therefore no transport by vorticity, but only convection due to agitation movements. It is often the case of putting in place the following repetitive cycle: Bandin - Shearing - Recombining
Special case of dispersions Liquids-Liquids dispersions and emulsions
It consists of mixing two immiscible liquids. We talk of dispersion in the case of a coarse unstable mixture and of emulsion in the case of a fine and stable mixture. We are in the presence of an aqueous phase (W) and an organic phase (O). The most common products identified with this definition are cosmetic creams, shampoos, mayonnaise, ice cream, alleviated butter, water paints.
Special case of kneading bread dough
The first phase of the bread production process is the dough mixing. These are the rheological characteristics of the dough, obtained during this phase, which largely determine the structure of the crump in terms of form and dimensions of gas bubbles in the dough. Dough mixing has the objective of mixing water, flour and other ingredients by providing a certain amount of energy. During mixing, a portion of the amount of water binds to flour starch and its proteins, while the remaining quantity of water is used to dissolve other ingredients such as salt and sugar.
Yeast bread / Sourdough bread / Poolish bread
The bread dough is subject to swelling of basic ingredients used, due to fermentation. That is what differentiates the flatbread and it is commonly called leavened dough. The flour comes mainly from bread-bound cereals characterized by the presence of gluten, protein groups of elastic properties that can imprison the carbon dioxide bubbles released by fermentation. This fermentation is initiated by the incorporation into the dough of micro-organisms such as yeast, in more or less important quantities depending on the flour and bread recipes.
Hydration of flour
The hydration rate of the dough is a fundamental parameter from both qualitative and economic points of view. Each flour has a basic hydration rate which depends of course of its own organic properties, but also of a number of external parameters. The technique of incorporating water into flour, that is to say the various dough mixing parameters, starting with the mixing, can have an influence on the ability of the baker to take maximum advantage of the hydration capacity of his flour.
Measure of the Energy Transferred during Kneading
For the past several years VMI has carried out research regarding the control of various parameters during kneading operations. In most cases, for small businesses or industrial manufacturing, the baker relies on criteria gathered by the sensorial examination of the dough to determine the optimum length of the kneading process. Efficiency and more specifically duplication factors have recently led some bakers to request a real time follow-up of the kneading process that takes into account the rheological characteristics of the dough being produced as well as the various operational parameters of the kneaders. The energy generated by the kneader and transferred to the dough is one of the physical values which meets this goal and can, with some precautions, provide precious benefits in the follow-up and optimization of a variety of settings.