The technique of ‘ autolysis – explained by the teacher Piergiorgio Giorilli
The dough is one of the main phases in the preparation of bread and bakery products in general. From its quality depend for about 80% of the characteristics of the finished product, for which a correct execution of the mixture is of a fundamental importance to obtain a finished product excellent. There are various methods in the preparation of a dough. The most common are: direct, in which all the ingredients are mixed in a single step; indirect, where before it is prepared as a Preimpastato chariot or poolish made of flour, water and compressed yeast that ferments at the end of which is inserted into the mixer and mixed with the other ingredients. The dough can also be prepared by the method semidirettoutilizzando pasta carryover or a pre-ferment. Furthermore, there are various techniques which intensified the dough, the dough hot etc ….Plays a ‘particular importance technique of autolysis. Its use gives numerous benefits to the final product, mainly due to the characteristics of the dough, the consistency of which is very smooth, elastic, malleable, able to absorb more water. The finished product acquires more volume and its crumb is very developed and fluffy. They also have benefits in terms organoleptic (taste and smell like) and storability. Before explaining the details of this technique, and the reason that using this method you have the benefits listed above, you should describe the processes of mix in general. In any mixture, regardless of its method of preparation, physical and mechanical processes take place, colloidal, biochemical and microbiological.
1. The physical and mechanical processes
The first stage is the formation of the dough which consists in mixing the ingredients and, providing energy (or manually or with the use of the mixer), forming a smooth and homogenous mass, which has a certain softness and a certain elasticity . The kneading is a very important process, from which depend on the characteristics of the dough and its behavior during the fermentation is that during the firing and, consequently, the quality of the finished product.
You need to mix all ingredients well, not only for incorporation in the dough evenly, but also because it is obtained by mixing the friction and the union at the molecular level of the chemical components of the flour and other ingredients, which form a homogeneous mass called ” dough “. The main reaction of this step is the formation of gluten. Wheat proteins have different sizes and during the dough cohesion forces combine the molecules of different sizes, forming a plastic mass and elastic, called gluten. Not all proteins, present in the flour have capacity to form gluten, but only those insoluble according to the classification of Osborne, with which all the flour proteins are divided into four groups according to their solubility and which are so divided
• albumins (water soluble)
• globulins (soluble in saline solutions)
• prolamins (soluble in alcohol)
• glutelins (soluble acids and bases)
Each of these fractions has different physical properties, are also their different molecular size, which increases going from albumin to glutelins. The gluten is formed only by the two fractions not soluble in water and in salt solutions (prolamin and glutelin), which are joined together under the action of water and of ‘energy, supplied to the dough. Protein molecules of a flour during the mixing, after having joined together, are ironed and are oriented so that the electronegative groups are subjected to the action of water. Then the protein content of the flour and the amount of water required are closely related to each other. The water added in the dough must never be in an amount such as to remain, even in part, free. The amount of water absorbed by depends on various factors, including the particle size, the protein content, the quality, the moisture of the flour and the presence of other ingredients in the dough, the hydrometric degree of the environment and the degree of consistency you want to have the dough. The mixtures containing more water must be mixed for longer, so that the water runs tied el ‘dough reaches optimum consistency. Also during mixing the dough appropriates a part of the air, it becomes less dense and softer. Oxygenate the dough is important not only to make it more soft and more flexible, but also to promote the fermentation process, as the oxygenation of the dough stimulates the vital activity of the yeasts. The action of oxygen strengthens the gluten, formed during kneading, because oxidize thiol groups of proteins in the flour, turning them into disulfide groups. The physical processes that occur during mechanical kneading are to change in physical and mechanical properties (strength and elasticity) of the dough, they depend on the mechanical revolutions. The effort that opposes a kneading the dough is not always constant and it changes depending on the characteristics of the dough. By measuring these efforts from the beginning of mixing, we can highlight three periods:
– The first period, after mixing of the ingredients, the effort of the mixer increases and this is due to the formation of gluten, which becomes more rigid and therefore opposes an increasing resistance to the kneader up to the maximum point, after which remain stable and then you can highlight
– The second period, when the effort of the mixer is always constant. In this period the mixture has the optimal characteristics (it is very smooth and rough extensibility). This is due to the fact that the gluten dough gaining extensibility, mind its resistance decreases, because it starts the reaction of proteolysis. In this period the dough is ready and should be removed dall’impastatrice, in fact it is very elastic and does not stick to the walls. Continuing the operation will worsen its features.
– The third period, namely when efforts dall’impastatrice are decreasing, the dough becomes more springs for an excessive heating and to the excessive mechanical stress occurs and the breakage of the gluten network.
For each mixture the time necessary to reach the optimal characteristics (second period) varies and depends on:
– the strength of the flour (the time of a mixture of weak flour is lower than the mixing time of a strong flour, as it has a resistance of gluten mesh minor);
– the type of mix (soft, soft, dry). The soft dough must be kneaded more, must have a temperature higher finishing and be mixed up to reach the top of their consistency. The dough should be fairly dry cold after ìimpastamento, removed before dall’impastatrice, even if they are not fully formed, because they generally are cylindered. During the calendering takes an additional heating of the dough and reaches its optimum consistency;
– the type of the mixer . For example, with a ‘kneading “spiral” the dough is formed earlier than a’ kneading machine with plunging arms, because the type “spiral” by more friction to the mixture. The mixer “fork” is the one that gives less effort and among all types is the slowest. During the heating the mixture takes place, due to the type of the mixer, and other factors, which varies from 3 ° C to 18 ° C.
2. The processes colloidal.
Mixing the flour and water, begins to form the complex colloidal very hydrated. The proteins of the flour are capable of absorbing and connect the quantity of water 2-3 times higher compared to their weight. The proteins, which belong to groups of prolamine and glutelin (insoluble in water and in salt solutions), absorbing water, swell, stretch and bind together by covalent bonds, disulfide etc., Forming gluten . In addition the dough will create the bonds dipolar, hydrogen (with water), ionic (caused by mineral salts, which in part are contained in the flour itself (phosphates, sulfates, chlorides etc ..) and in part added, such as sodium chloride (salt). The addition of salt in percentages moderate (around 2%), the better the strength and elasticity of the dough, the ability to retain the gas and ultimately the volume of the bread, while high amount of sodium chloride due to the formation of an excessive number of ionic bonds that make the dough too stiff and rigid. The starch, whose quantity in the mixture is conspicuous, absorb water and form the electrostatic bonds with gluten , creating a homogeneous mesh. Even the dough lipids (especially polar ones, such as mono- and diglycerides) have the ability to bind with proteins, forming the lipo-protein complexes, thereby improving the extensibility and the retention capacity of the gas by the dough.
The gluten thus formed absorbs the water, liquids and gases present in the dough, not only on the surface, but also in depth, which causes swelling of the gluten mesh itself. The dough can be imagined as a complex system that includes three phases: solid, liquid, gaseous.
The solid phase
The solid phase of the mixture is represented by the insoluble proteins (linked together in the gluten mesh), from the granules of the starch and from residues of the bran. The granules of the starch does not have the same capacity for absorption of liquids such as gluten (they absorb only 30-35% of water by their mass), and therefore do not increase so much of their volume. However, whereas there is much starch in the flour, the amount of water will be absorbed more or less equal to that absorbed by proteins. The capacity for water absorption of the starch granules increases with their being damaged during grinding (unless they are excessively damaged, otherwise absorb less water). The residues of the bran are those which absorb the greater amount of water (up to 800% of their weight).
The liquid phase
Besides water, the liquid phase belong all other substances that are in solution: the proteins soluble in water and in salt solutions (groups of albumins and globulins), the mineral salts and sugars, dissolved respectively in water , dextrin. Also the pentosans (gels) belong to the liquid phase of the dough. The liquid phase can be located around the surfaces of the solid phases and also of being absorbed inside.
The gaseous phase
It is made from dall’impasto forfeited during the kneading and by the carbon dioxide produced during fermentation.
A fragment of the mixture can be represented in this way:
3. The biochemical processes.
Are the processes of transformation of lipids, carbohydrates, proteins and other chemical components of the flour and the dough with the help of the enzymes in the flour and baking powder. The reactions that occur in the dough are numerous and complex. During kneading you create several links (covalent, dipolar, ionic, hydrogen, electrostatic etc.) Between the proteins forming gluten and other components (soluble proteins, minerals, starch, lipids etc.). building a uniform and homogeneous material called “dough.”
Furthermore, with the help of enzymes of the flour, activated with water, the dough begin the reactions of hydrolysis of the protein and starch. Under the action of proteases, protein flour begin disintegrate into peptides (the reaction of proteolysis), helping the dough to become softer and plastificabile. This process takes place in each dough, however, can be more or less active, depends on various factors (enzyme activity of the flour, the properties of gluten, dough temperature etc.). Also in the mixture of starch hydrolysis occurs under the action of amylase, which begins dall’impastamento, but develops more than anything else during the fermentation, making the foods (sugars) to the yeast cells, and for this reason has considerable importance. Although this process (the saccariferazione starch) liquefying the action takes place in the dough. Addition reactions take place in the transformation of sugars and lipids. The behavior of the latter has a dual effect: for themselves increase the extensibility of the gluten network and make the dough more pliable, if they are processed with the help of enzymes (lipase and lipossiasi) in substances peroxides (this process is partially and has a lower intensity) cause the opposite effect, because the latter makes the gluten stronger and more rigid.
4. The microbiological processes.
The microbiological processes (which concern the microflora of the dough) are: the multiplication of the cells of yeast and lactic acid bacteria and also the alcoholic fermentation and lactic below. During the kneading takes an active multiplication of these microorganisms, which begin to ferment during the first fermentation (also called “bet”) of the dough. The purpose of the fermentation is to obtain a mixture that has the optimal properties for its forming, and below the leavening and baking. During fermentation processes continue colloidal and biochemical: the granules of starch and the other components of the solid phase of the mixture continue to absorb gases and liquids; Furthermore, the gaseous phase increases for the formation of CO2 produced by the yeast, and then increase the volume of the dough and its softness. During fermentation, change the properties of the gluten molecules of gluten proteins continue to swell by absorbing the carbon dioxide produced by the yeast, relaxing and bind between them, making the mixture more spongy, also the reaction occurs proteolysis , which makes the dough more pliable. The main processes that occur during fermentation of the dough are the alcoholic fermentation and lactic.
Autolysis. The process and chemical aspects
The autolysis is a special technique that allows you to take advantage of the self-evolution of the characteristics of gluten. This system is practiced in three phases: initial mixing of the flour with water;autolytic rest of the dough so obtained; and in the end the final mixture. In the first stage dough are dosed the basic ingredients (flour and water (55%)), which are gently mixed (for example with the spiral kneading 5-8 minutes, only in the first speed). The dough thus obtained, is subsequently the rest (second phase), which can last from 20 minutes to 24 hours. If the rest period is longer than 5-6 hours, you may want to add to the mix a portion of salt and do not exceed 45-50% water, the subsequent storage should be carried out at a temperature of + 18-20 ° C. While for the rest period short enough the dough is left to the environment, possibly in the same tank revolutions. Finally follows the third stage (the final mixture), in which are added the missing ingredients in the recipe (yeast, malt, possibly water, salt), or other ingredients according to the recipe. The whole is mixed only in the second speed for the time necessary. The dough autolytic can be used totally or partially (with the minimum dose of 20%).
The technique of autolysis allows to obtain the final product, marked by three characteristics: a distinctive flavor, a great development and a longer shelf-life. Also reduces the time of mixing, the consistency of the dough becomes very smooth and malleable, it has a molding easier and the finished product has a higher volume, better alveolation and greater softness of the crumb.
These peculiarities in the product are the result of the physical, chemical and colloidal who take the field during the rest of the dough. In this phase the gluten undergoes changes (lysis) by enzymes (in particular amylase and protease), activated by the water of the dough. Under the action of the enzymes amylase, as has already been discussed, the starch is converted into sugars, providing more available sugars in the dough, thus facilitating the fermentation below and bringing to the final product the best organoleptic characteristics (such as the taste and the scent more intense). The protease enzymes are the protagonists of the reaction of proteolysis, the reaction, which occurs in any of the dough and takes development, especially during the rest period of the paste. With this reaction the gluten dough is broken into smaller pieces, the protein chains thus obtained are getting longer, the pasta, a greater extensibility, become more malleable. The reaction of proteolysis may be more or less active depending on the various elements (the structure of proteins (in particular the properties of gluten), the enzymatic activity of the flour, the presence of certain substances in the dough, dough temperature etc. ..). We explore this topic:
The structure of proteins
Proteins are made from amino acids and can be disposed of in shorter fragments (called peptides) under the action of the protease enzyme. Proteolysis is the reaction to the disintegration of proteins. This reaction disintegrates the globular structure of the protein. The proteolysis happens in each dough, however, may be more or less active, can involve more or less protein. The more active will be the reaction of proteolysis, the dough will become much softer . Proteolysis, destroying proteins, involved in the gluten network, lowers its capacity to water absorption and retention of carbon dioxide. So the progress of this reaction decreases the strength of the dough and increases its extensibility. The activity of the reaction depends dall’attaccabilità proteolysis of proteins by enzymes. The factors that determine the stickiness of proteins are the following:
- The presence of certain groups (thiol or disulfide)
The structure of proteins is quite complex, in addition to peptide bonds are also present other bonds, including, for example, those that involve the two sulfur atoms, so-called the disulfide bridges (-S = S-). So, in the proteins you can highlight groups thiol (-SH-) or disulfide (-S = S ).
A flour, which proteins possess most of the groups disulfide (-S = S), has less stickiness. This flour has a gluten stronger and more robust (reinforced by disulfide bridges).
Instead, the presence of thiol groups (-SH-), easily attacked by proteases, due to the formation of a gluten network rarer and weaker.
With the denaturation increases the stickiness of the proteins.
occurs when the protein, reacting to heat, lose the compact structure (globular) and are transformed into an intermediate position between the globular structure and fibrillar. With this process discarding the disulfide bonds of the protein, so after they are easily attacked by proteases. The denaturation of the proteins to the heat occurs in the dough prepared with the technique hot.
the quality of the wheat, which was produced flour
Concerns the genetic characteristics of the grain (which determine the protein content and chemical composition of proteins) and the climatic characteristics of its maturation (usually in warmer climates and drier the grains reach the highest protein values).
Particular importance has the same chemical composition of gluten.
The flour protein, insoluble in water and in salt solutions, have the ability to form during the dough an elastic structure, compact and spongy, called gluten. The strength of the flour is more dependent on the properties of gluten.
The higher the content of the gluten, the stronger is the flour .
Gluten is the one, which supports the dough, serves essentially the function of the load-bearing walls in a house. However, the amount of gluten does not determine everything, are also important characteristics. The two flours may have the same amount of gluten, however, a may be louder and the other weaker.
Gluten is composed of the prolamins (mostly represented by the protein gliadin) and glutelin (especially where there is the protein glutenin).
The gliadin in contact with the water forms a sticky mass and fluid, instead glutenin absorbing water, forms a compact mass, elastic and resistant.
The wet gluten possesses all the mechanical properties of the two proteins (gliadin is that of glutenin). Obviously, a flour to be stronger in the majority must have glutenins . If a flour has a high amount of gluten, but this is mainly composed by gliadin, the flour can not be very strong, because its gluten is soft and slightly spongy.
- The time of conservation of the flour
In a flour rested the stickiness of the protein decreases, however, in a flour expired, is too high.
The enzymes protease
Proteases are enzymes, contained in wheat, capable of undoing the proteins. Proteases unmake the globular structure of proteins, amino acids without going to, as they do not have the ability to destroy all the peptide bonds .
Also the protease can be found in the passive and in active form, depending on the groups contained in their structure (thiol or disulfide):
Pr-S = S-Pr Protease in passive form
Pr-SH Protease in active form
The activators and inhibitors of proteolysis
Activators of proteolysis are those substances, which transform the protease from passive in active form and favor with this reaction of proteolysis. Are substances that weaken the flour.
For example, are part of the glutathione and cysteine, the substance of protein nature, content in wheat germ and yeast.
The inhibitors of proteolysis , however, are those substances that produce the active form by proteases in passive form. Are the substances that strengthen the flour. As examples of inhibitors of proteolysis can list peroxides, oxygen, vitamin C and also oxidants like potassium iodate (KJO3) and potassium bromate (KBrO3). Also occurs in the dough autolytic an opposite reaction to proteolysis, or the reinforcement of the gluten network due to the action of the oxygen of air incorporated from the dough during kneading. Under the action of oxygen groups of the gluten network (SH) are transformed into disulfide bridges (-S = S), gluten is strengthened, becomes more elastic and can absorb larger quantities of water. This reaction takes development especially during dough (in the first phase of autolysis and the last stage (the final dell’impastmo)), to a lesser extent also occurs during the rest of the dough. During the rest of the dough the gluten is converted, thanks to these two reactions (that of proteolysis and that of oxidation), the protein chains get longer, they swell by absorbing the air and water, complete their hydration, so the dough during its final processing reaches the top of its consistency in shorter period, with the largest quantities of water. All in all autolysis is a technique that gives the dough a particular extensibility, but at the same time improves the elasticity and the degree of absorption of water, they also reduce the time and kneading dough is very smooth . This technique can be particularly useful for baking with the natural yeast, or when they are used flour, particularly resistant.