Abstract:
The invention relates to a method of kneading dough in order to produce bread or similar products. According to the invention, the dough ingredients are introduced into a chamber and all of said ingredients are subsequently kneaded. The inventive method is characterised in that it comprises: a vacuum phase during which a vacuum is applied in the chamber; and one or more phases involving the introduction of gas, during which a gas containing oxygen is introduced into the chamber. The aforementioned vacuum phase continues more or less throughout the entire kneading phase, with at least one part of each introduction phase taking place simultaneously with the kneading phase. The invention also relates to a device that is used to carry out said method.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Phase Application of PCT/FR02/03542, which claims priority to French Patent Application No. 0113521, filed Oct. 19, 2001, entitled “Vacuum Kneading Method with the Introduction of Oxygen and the Device Used to Carry Out Said Method,” both of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     The invention concerns a method of kneading dough for making bread or similar products and a device for implementing the said method. 
     The document EP-A-0 246 768 describes a method and apparatus for kneading bread dough in an oxygen-enriched atmosphere. To this end, oxygen or oxygen-enriched air is introduced into the chamber of the apparatus contained in the dough before or during kneading. The atmosphere in the chamber is then discharged through a discharge pipe. This addition of oxygen promotes the action of the ascorbic acid, used as a single improving product (known as an improver in the technical field). 
     This document describes that the application of a partial vacuum in the chamber is not necessary but that it can be implemented before the introduction of the oxygen or the oxygen-enriched air. 
     However, this method does not make it possible to control the development of the bubble structure in the bread dough. 
     According to the document EP-A-0 629 115, it is known that the production of a partial vacuum during kneading improves the uniformity of the structure of the soft part of the bread. However, the creation of a partial vacuum removes the air, which reduces the oxidation of the improvers used by bakers (ascorbic acid or potassium bromate) for intensifying the formation of the gluten lattice and, stabilising the structure of the bubbles. 
     The document EP-A-0 629 115 describes a dough kneading method for optimising the use of ascorbic acid as an improver. To this end, the method comprises the kneading of the dough ingredients in the presence of air or a gas containing oxygen. During a first phase of this kneading, an overpressure is applied to the atmosphere surrounding the dough, whilst a reduced pressure is applied during a second phase of the kneading. The first phase allows oxidation of the ascorbic acid, the second phase controlling the structure of the bubbles in the dough. 
     This method has the drawback of requiring two kneading phases, including one phase under air overpressure which is difficult to achieve with normal kneading means. 
     This is because high forces are exerted by the air pressure on the mixing chamber and on its mechanical environment such as for example the mixing tool or tools, the sealing joint or joints, and the lid of the vessel. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The invention aims to resolve the aforementioned drawbacks of the prior art by proposing a method affording adequate oxygenation of the dough at the same time as controlling the structure of the bubbles within it. 
     The method thus optimises the uniformity of the structure of the soft part of the bread whilst guaranteeing sufficient oxygenation thereof. 
     To this end, a first object of the invention is a method of kneading dough for making bread or similar products, in which the ingredients of the dough are introduced into a chamber, and then the said ingredients are kneaded together, characterised in that it comprises:
         a negative-pressure phase during which a negative pressure is applied in the chamber ( 2 );   a phase or several phases of introducing gas G during which a gas G containing oxygen is introduced into the chamber ( 2 );
 
the negative-pressure phase lasting for substantially the entire duration of the kneading phase, at least part of each introduction phase being simultaneous with the kneading phase.
       

     No overpressure with respect to atmospheric pressure is thus applied in the chamber, which avoids the application of stresses. In a variant, the negative-pressure phase begins just a little time before or after the start of the kneading phase and/or finishes just a little time before or after the end of the kneading phase. 
     In another variant, the gas introduction phase or phases begin just a little time before or after the start or end of the kneading phase, and/or finish just a little time before or after the start or end of the kneading phase. 
     In one embodiment, the method comprises a single phase of introducing the gas G which lasts substantially throughout the kneading phase. 
     In another embodiment, the method comprises several introduction phases, the intervals of time between these phases and the duration of each of these phases being variable. 
     Each introduction phase can last from a few seconds to several tens of minutes. 
     Moreover, during each introduction phase, it is possible to vary the flow rate of gas G. 
     And during the negative-pressure phase, it is possible to apply an absolute pressure in the chamber ( 2 ) of between 0.02 bar and 0.98 bar. 
     In a variant, the gas said (G) can be introduced into the chamber ( 2 ) in the volume of the dough (P). 
     A second object of the invention is a device implementing the method described above. 
     This device comprises a chamber formed by a vessel intended to contain the dough and a removable lid hermetically closing the said vessel, and kneading means comprising a rotor. 
     The said device is characterised in that it comprises gas supply means opening out in the chamber and pipes for discharging the atmosphere from the chamber opening out in the chamber at a distance from the dough. 
     In a variant, the said supply means and the said discharge pipes are disposed on substantially opposite parts of the chamber. 
     In one embodiment, the said discharge pipes are connected to at least one vacuum pump. 
     In another embodiment, the said feed means open out in the bottom part of the said chamber. 
     The gas then passes through the dough before being discharged, forming air bubbles therein. The dimensions of these air bubbles are very rapidly reduced by virtue of keeping the chamber under partial vacuum. 
     In a first embodiment of the device, the axis of the rotor of the said device is horizontal and the fixing and sealed guidance of the rotor with respect to the said vessel are achieved by means of two bearings, each bearing comprising in particular
         a bearing body comprising means of fixing to the vessel, and having a central recess or seat for the end part of the rotor to pass;   sealing means arranged for providing the dynamic sealing of the chamber;   a jacket in the form of a substantially cylindrical part of revolution, fitted on the said end part of the rotor and interposed between it and the bearing body, the sealing means being disposed between the seat of the bearing body and the jacket.       

     The means of supplying gas to the vessel are then situated at the means of sealing the said bearing. 
     This configuration makes it possible to use means already existing for the introduction of the gas. 
     In a variant, the said bearing sealing means comprise a plurality of lip joints fitted in a housing of the seat, the lips of the joints cooperating with a first end part of the jacket turned towards the vessel, at least one of the joints being oriented so that its lip is turned towards the vessel, whilst at least one of the other joints is oriented so that its lip is turned in the opposite direction. 
     In this variant, the gas supply means open out in the housing between the vessel and the said joint whose lip is turned towards the vessel. 
     In another variant, the said bearing sealing means comprise a plurality of lip joints fitted in a housing of the seat, the lips of the joint cooperating with a first end part of the jacket turned towards the vessel, two juxtaposed joints being oriented so that the lip is turned towards the vessel whilst at least one of the other joints is oriented so that its lip is turned in the opposite direction. 
     In this variant, the gas supply means open out in the housing between the said juxtaposed joints whose lip is turned towards the vessel. 
     The gas arriving under overpressure then raises the joint disposed between the supply means and the vessel. In addition, the passage of the gas between the two joints prevents the dough from being introduced into this space, guaranteeing the hygiene of the latter. 
     In a second embodiment of the device the axis of the rotor of the device is horizontal and the vessel is asymmetric with respect to a vertical plane P passing through the rotation axis of the rotor. 
     The vessel comprises a first substantially vertical side wall, and a second side wall inclined by a given angle to the vertical. The curved vessel bottom connects the first wall to the second side wall, so that the vessel comprises, on the side of the second side wall, a space widening out towards the top in the form of a crescent, situated between the second side wall and the path followed by the free end of the rotor blades. 
     In this embodiment, the gas supply means open out in the said space. 
     Thus the supply means open out outside the passage of the rotor blades and are easily accessible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the invention will emerge during the following description of embodiments, with reference to the accompanying drawings, given by way of non-limiting examples, in which: 
         FIG. 1  is a schematic representation of a device implementing the kneading method of the invention; 
         FIG. 2  is a view in axial section of a first embodiment of the device in  FIG. 1 , said device comprising a vessel and a rotor rotatably fixed on the vessel by two sealed roller bearings; 
         FIG. 3  is an enlarged view of the sealing means of the sealed bearings of the device in  FIG. 2 ; 
         FIG. 4  is a variant of the sealing means depicted in  FIG. 3 ; 
         FIG. 5  is a view in axial section of a second embodiment of the device in  FIG. 1 ; 
         FIG. 6  is a diagram representing the starting of the rotor as a function of time during the kneading phase; 
         FIG. 7  is a diagram representing possible profiles of the negative pressure in the chamber as a function of time and; 
         FIG. 8  is a diagram depicting possible profiles of the gas flow as a function of time. 
     
    
    
     The X-axes of the diagrams depicted in  FIGS. 6 to 8  coincide so as to be able to compare the durations of the various kneading, negative pressure and introduction phases of the method. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  depicts schematically a kneading device  1 , comprising a chamber  2  formed by a vessel  3  intended to contain the dough P and a removable lid  4 , hermetically closing the said vessel  3 , and providing its static sealing. 
     The said device  1  also comprises kneading means  5  comprising a rotor  6 . 
     The rotation axis X of the rotor  6  can be either vertical or horizontal. The horizontalness being defined with respect to the floor on which the device  1  is resting, the vessel  3  being able to be fixed or tilting. 
     In the embodiments in  FIGS. 2 to 5 , the axis X of the rotor  6  is horizontal. 
     The rotor  6  is mounted for rotation in the vessel  3  and is actuated by a motor  7 . 
     Supply means  8  open out in the chamber  2  and for example in the vessel  3  to allow the introduction of a gas G containing oxygen into the said vessel. 
     In one embodiment, the supply means  8  open out in the bottom part of the vessel  3 , in the volume of the dough P, so that the gas G passes through the dough P. 
     These supply means  8  are for example nozzles or openings situated on the vessel  3  and connected to one or more reservoirs  9  of gas G. It is also possible to use, as gas supply means  8 , means of supplying water to the said chamber  2 . 
     A regulation valve  10  can also be provided for regulating the flow of gas G in the supply means  8 . 
     It is thus possible to regulate the flow of gas G, in particular according to the nature and quantity of dough, the volume of the vessel and the required result. 
     One or more flow meters  11  can be used for measuring the flow of gas G introduced by the supply means  8  into the chamber  2 . 
     The device  1  also comprises one or more pipes  12  for discharging the atmosphere present in the chamber  2 . These pipes  12  open out in the chamber  2  at a distance from the dough P. They can be situated on the lid  4  or on the top part of the vessel  3 , above the dough P. 
     These discharge pipes  12  are connected to at least one vacuum pump  13 , which provides a partial vacuum in the chamber  2 . The atmosphere in the chamber is thus under negative pressure with respect to the atmospheric pressure outside the chamber and with respect to the pressure in the supply means  8 . 
     Pressure measurement means, such as pressure gauges, can be used for measuring the pressures in the supply means  8  and in the chamber  2 . 
     The functioning of the vacuum pump or pumps  13  is adjusted so that no overpressure with respect to atmospheric pressure is applied in the chamber  2 . 
     Thus the gas G is introduced into the chamber  2  through the supply means  8  and is then sucked into the discharge pipes  12  by the vacuum pump or pumps  13 . A circulation of gas is thus caused in the chamber  2 . This circulation is represented by the arrows F in the figures. 
     The gas supply means  8  and the discharge pipes  12  can be disposed on substantially opposite parts of the chamber  2  in order to help the gas G to pass through the dough P. 
     The pressure in the chamber  2  is such that it is lower than the pressure in the supply means  8  and/or the reservoir  9 . 
     A pressure difference is thus created in the chamber  2  and the reservoir  9  of gas G, assisting the introduction of the gas G into the chamber  2 . 
     The pressure difference can be accentuated by increasing the gas pressure in the reservoir  9  and/or in the supply pipes  8 . 
     Particular embodiments of the device  1  and of the supply means  8  are now described in detail. 
     In a first embodiment, with reference to  FIGS. 2 to 4 , the axis X of the rotor  6  is horizontal and the fixing and sealed guidance of the rotor  6  with respect to the said vessel  3  are achieved by means of bearings  14 . 
     One of the bearings  14  is now described in detail, assuming the two bearings to be identical. 
     The bearing  14  comprises a bearing body  15  which has a through central recess  16  called a seat, having symmetry of revolution, and in which an end part  17  of the rotor  6  is inserted. 
     The bearing body  15  is fixed to a side wall of the vessel  3  on the external side, by means of removable fixing means  18  such as screws regularly distributed over the circumference of the bearing body  15 . 
     The bearing body  15  is fixed in line with an opening  19  formed in the said side wall of the vessel  3 , so that the axis of revolution of the seat  16  coincides with the rotation axis X of the rotor  6 . 
     The bearing  14  is designed to provide a total seal of the inside of the vessel  3  with respect to the ambient atmosphere outside it. 
     To this end, the bearing  14  comprises dynamic sealing means  20  comprising a plurality of lip joints  21 ,  22 ,  23  mounted in series and fitted in a part of the seat  16  called a housing  24 , adjacent to the opening  19  formed in the side wall of the vessel  3 . 
     In the embodiment illustrated in  FIG. 3 , three lip joints  21 ,  22 ,  23  are provided, between a shoulder  25  of the housing  24  and an internal circlip  26  inserted in a groove formed in the housing  24 . 
     The joints  21 ,  22 ,  23  are arranged both to provide the dynamic seal for the vessel  3  and to maintain it under pressure, the pressure inside the vessel being able to be lower than atmospheric pressure, for example 50 millibars, whilst the speed of rotation of the rotor in operation is generally between 10 revolutions per minute and 250 revolutions per minute. 
     To this end, at least one  21  of the joints, for example the one closest to the vessel  3 , is oriented so that its lip is turned towards the inside of the vessel  3 , whilst at least one  23  of the others is oriented so that its lip is turned towards the outside of the vessel. 
     Means  8  of supplying gas G to the vessel  3  are situated at the sealing means  20  of the said bearing  14 . 
     To this end a bore is provided in the bearing body  15  in order to introduce the gas G. 
     This bore opens out on the one hand in the housing  24  of the sealing means  20  and on the other hand outside the bearing, on a part of the external surface of the bearing which is not in contact with another piece. 
     In the first variant in  FIG. 3 , the lips of the joints  21 ,  22  cooperate with the end part  17  of the jacket  32  turned towards the vessel  3 , the two joints  21 ,  22  being oriented so that their lip is turned towards the vessel  3 , whilst the other joint  23  is oriented so that its lip is turned in the opposite direction. 
     In this variant, the means  8  of supplying the gas open out in the housing  24 , between the juxtaposed joints  21 ,  22 . 
     The difference in pressure between the chamber  2  and the supply means  8  thus assist the raising of the lip of the joint  21  and the passage of the gas G to the chamber. 
     In the second variant in  FIG. 4 , only two juxtaposed joints  22 ,  23  are used, the two joints  22 ,  23  being oriented so that their lip is turned respectively towards the vessel  3  and in the opposite direction. 
     The gas supply means  8  then open out in the housing  24  between the vessel  3  and the said juxtaposed joints  22 ,  23 . 
     These supply means  8  can be disposed on the two bearings  14  of the rotor, or on one of the two. It is also possible to envisage the production of one or more bores in a bearing  14  for introducing the gas G. 
     The gas is thus introduced as close as possible to the dough, directly on the rotor. 
     One embodiment of the structure of a bearing  14  is now described in detail with reference to  FIG. 3 . 
     In order to ensure rigid holding of the joints  21 ,  22 ,  23  in their housing  24  between the shoulder  25  and the circlip  26 , at least one spacer  27  can be inserted between two successive joints  21 ,  22 . 
     In addition, in order to provide the rotational guidance of the rotor  6 , the bearing  14  comprises at least one roller bearing  28  interposed between the bearing body  15  and the end part  17  of the rotor  6 . 
     The bearing  28  comprises a fixed external ring  29 , associated with the bearing body  15  whilst for example being fitted in a bore  30  of the seat  16 , a movable internal ring  31 , and bodies rolling on each other, such as balls, needles or cylindrical or conical rollers. 
     The lip joints  21 ,  22 ,  23  and the bearing  28  are not in direct contact with the end part  17  of the rotor  6 . 
     This is because the bearing  14  comprises an intermediate piece  32  of revolution, substantially cylindrical and hollow, called a jacket, fitted on the end part  17  of the rotor  3  and interposed between the said part and the bearing body  15 . 
     The jacket  32  has a first end part  33  turned towards the inside and inserted in the seat  16  of the bearing body  15 , and a second opposite end part  34 , projecting from the seat  16  towards the outside. 
     The roller bearing  28  is interposed between the seat  16  of the bearing body  15  and the jacket  32 , its inner race  31  being fitted on the jacket  32 , and mounted clamped between a projecting shoulder  35  on the jacket  32  and a nut  36  screwed on the threaded part  37  of the jacket  32 . 
     In addition, the lip joints  21 ,  22 ,  23  are interposed between the bearing body  15  and the jacket  32 , their lips being in contact with the first end part  33  of the jacket  32 . 
     In addition, in order on the one hand to provide the clamping of the outlet race  29  of the bearing  28  and on the other hand to ensure a complementary seal on the bearing  14 , the latter comprises a cover  38  associated with the bearing body  15 . 
     To this end the cover  38  comprises a cover body  39  in the form of a part of revolution having a central recess  40  for passage of the end part  17  of the rotor  6  and of the second end part  34  of the jacket  32  fitted thereon. 
     The cover  38  also comprises removable means  41  of fixing the cover body  39  to the bearing body  15 , on the opposite side to the vessel  3 , that is to say on the side turned towards the outside. 
     These fixing means  41  are for example in the form of a plurality of screws regularly distributed over the circumference of the cover body  38 . 
     In addition, the cover comprises a lip joint  42  interposed between the cover body  39  and the jacket  32 . 
     The lip joint  42  is for example fitted in a housing  43  provided in the central recess  40  of the cover body  39 , its lip being in contact with the second end part  34  of the jacket  32 . 
     In addition, the jacket  32  has an end  43  projecting from the cover  38  towards the outside. 
     In order to connect together, at least with respect to rotation, the jacket  32  and the end part  17  of the rotor  6 , the bearing comprises an annular clamping collar  44  enclosing the end  43  of the jacket  32 , this collar forming a means for the removable fixing of the jacket  32  to the rotor  6 . 
     In a second embodiment, with reference to  FIG. 5 , the device is such that the axis X of the rotor  6  is horizontal and the vessel  3  is asymmetric with respect to a vertical plane P 1  passing through the rotation axis X of the rotor. 
     The vessel comprises a first substantially vertical side wall  45  and a second side wall  46  inclined by a given angle to the vertical. 
     The curved vessel bottom connects the first wall  45  to the second side wall  46 , so that the vessel  3  comprises, on the same side as the second side wall  46 , a space  47  opening out towards the top in the form of a crescent. 
     This space  47  is situated between the second side wall  46  and the path followed by the free end of the rotor  6  blades. This path is represented by the curve C in  FIG. 5 . 
     The gas supply means  8  open out in the said space  47 , outside the passage area of the rotor  6  blades, and are thus easily accessible. 
     A particular arrangement of the walls  45 ,  46  of the vessel  3  is described below. 
     The internal face  48  of the first side wall  45  comprises a vertical rectilinear portion  49  and a curved portion  50 , connected at a junction  51 . The junction  51  belongs substantially to a horizontal plane P 2  passing through the axis X of the rotor  6 . Thus the path C of the blades is substantially tangent to the internal face  48 , in fact separated by a space e, substantially from the junction  51  over approximately ¼ of a turn as far as the bottom vertex S 1  of the path C. The circular path C matching the shape of the internal face  48 , the portion  49  is tangent to the vertex S 2  of the path C. 
     The internal face  48  of the second side wall  46  comprises a rectilinear portion  52  and a curved portion  53 , connected at a junction  54 . 
     Along the second side wall  46 , the distance between the tangent to the path C at the vertex S n  and the intersection I n  between the second wall  46  and the radius R 1  of the path passing through the intersection I n  is defined as d n . 
     On the same side as the second side wall  46 :
         the portion  52  is inclined by an angle β of around 10° to the vertical;   the intersection I n  is separated from the vertex S n  by the distance d n .       

     Thus the plane P 2  intersects the second side wall  46  at the intersection I 1 , the vertex Sn is marked with the reference  55 , the intersection I 1  and the vertex  55  are spaced apart by the distance d 1 . 
     An angle δ is defined between on the one hand the vertical plane P 1  passing through the axis of the rotor  6  and on the other hand a plane P 3  passing through the axis of the rotor  6  and the junction  54  between the portion  52  and the portion  53 . The best results obtained correspond to a value of δ of around 100°. 
     It is possible to use a device comprising a vessel  3  as described in the second embodiment and where the fixing and sealed guidance of the rotor  6  with respect to the said vessel  3  are achieved by means of bearings  14  described in the first embodiment. 
     The supply means  8  described in these embodiments can then be used in combination or alone. 
     The dough kneading method is now described. 
     During a first step, the lid  4  is opened so as to allow the introduction of the ingredients of the dough P into the chamber  2 . 
     These ingredients comprise in particular flour, water and other elements used in baking. Amongst the latter, ascorbic acid can be used as an improver. However, good results are obtained with the method of the invention without using ascorbic acid. 
     The ingredients are then introduced into the chamber and the lid  4  is closed again hermetically in order to ensure that the chamber  2  is sealed. 
     The rotor  6  is then started up so as to stir the ingredients of the dough P. The functioning of the rotor corresponds to the kneading phase. 
     The method also comprises:
         a negative-pressure phase during which a pressure below atmospheric pressure is applied in the chamber  2 ,   one or more phases of introducing the gas G containing oxygen during which the gas G is introduced into the chamber  2 .       

     The negative-pressure and introduction phases help to create a circulation of gas in the chamber  2 . 
     The negative-pressure phase lasts substantially throughout the kneading phase. 
     It can begin just a short time before or after the start of the kneading phase and end just a short time before or after the end of the kneading phase. 
     Several introduction phases can be applied during the kneading phase. The intervals of time between these phases and the duration of each of these phases can be variable. 
     Each of these introduction phases takes place substantially during the kneading phase. A phase can however begin or end just a little time before or after the start or end of the kneading phase. 
     Thus at least part of each introduction phase and the kneading phase are simultaneous. 
     A kneading phase lasting from a few minutes to several tens of minutes, each phase of introducing the gas G can last from around a few seconds to several tens of minutes. Thus a phase can last substantially throughout the kneading only for a short time during the kneading. 
     The introduction of the gas G for a period less than the kneading time is implemented to the detriment of oxygenation but does however assist the reduction of the structure of the alveoli in the soft part of the bread obtained. 
     During the introduction phase, the rate of introduction of the gas G can be varied according to requirements. This rate can also vary from one phase to another during the same kneading phase. 
     During the negative-pressure phase, the negative pressure in the chamber  2  is achieved by means of vacuum pumps  13  which function as long as the pressure in the chamber  2  is to be reduced. 
     In particular, in the absence of introduction of the gas G, the functioning of the vacuum pumps  13  can be suspended if the seal on the chamber is sufficient for a negative pressure to be maintained in the latter. 
     During the negative-pressure phase, the absolute pressure applied in the said chamber  2  can be between 0.02 bar and 0.98 bar. It is possible to vary this pressure during the negative-pressure phase. 
     The number and duration of the gas introduction phases, as well as the duration of the negative-pressure phase and the value of the pressure applied to the chamber during this phase, depend in particular on the nature and quantity of the dough P, the volume of the vessel and the result required. 
     During the kneading, the speed of rotation of the rotor  6  can be varied in order to adapt it to the product required. The duration of the kneading phase is then in general longer and longer as the speed of rotation of the rotor  6  is reduced. 
     At the end of the kneading phase, the functioning of the rotor  6  is stopped and, when the pressure in the chamber  2  is equal to the atmospheric pressure, the lid  4  is lifted off and the dough can be removed. 
     In a variant of the method, during the phase of introduction of the gas G into the chamber  2 , the gas G is introduced into the chamber  2  in the volume of the dough P, so that the circulation of gas passes through the dough P. 
     In another variant, the gas G is introduced into the said chamber using the device for supplying water to the said chamber  2 . 
     The gas containing oxygen can be air or any other gas containing oxygen suitable for producing the food dough. 
     Finally, control means can be provided for regulating the various parameters of the method such as the pressure in the chamber and/or in the supply pipes, the flow of gas G, the speed of rotation of the rotor and the duration of the various phases. 
     Examples of durations of the various phases are described below with reference to  FIGS. 6 to 8 . 
       FIG. 6  depicts the functioning of the rotor as a function of time, the curve obtained representing the duration of the kneading phase. 
       FIG. 7  shows the pressure in the chamber  2  as a function of time. Thus curves a, b represent examples of change in the pressure during the negative-pressure phase. 
     Curve a (in a continuous line) corresponds to a phase during which the pressure in the chamber  2  is progressively reduced. The reduction in the pressure begins just a short time after the start of the kneading phase and stops just a short time after the end of the kneading phase. 
     Curve b (in a broken line) corresponds to a rapid reduction in the pressure just a little time before the start of the kneading phase, the pressure increasing once again just a little time before the end of the kneading. 
       FIG. 8  depicts the flow of gas G introduced into the chamber  2  as a function of time. Each curve c, d represents a phase of introducing the gas G. 
     Curve c (in a continuous line) corresponds to a single introduction phase during which the introduction of the gas commences just a little time after the start of the kneading phase and ends just a little time after the end of the kneading phase. During this phase, the gas flow varies as a function of time. Such a phase can for example be combined with the negative-pressure phase represented by curve a in  FIG. 7 . 
     Curve d (broken line) consists of three curves d 1 , d 2  and d 3  corresponding to three introduction phases. During each of these phases, the gas is introduced at a constant rate, the rate varying from one phase to another. The durations and the intervals between these phases are variable. 
     All these three phases, each of the phases, or all combinations between two of these phases can be combined with the negative-pressure phase represented by curve b in  FIG. 7 . 
     An example of an implementation of the method is described below. 
     In this example, the device  1  described in the first embodiment is used. The volume of the vessel  3  is 400 liters. 
     The gas employed is air and the latter is introduced through the two bearings  14  of the rotor. 
     For 260 kg of bread dough, the following conditions are used for obtaining a good-quality bread dough:
         duration of the kneading phase: 6 minutes 30 seconds;   at each bearing  14 : introduction of air at a flow rate of 50 liters per minute and a pressure of 3 bar in the supply means  8 ;   pressure in the chamber  2 : −0.8 bar, and the absolute pressure in the chamber  2  is then 0.2 bar.       

     The phases of negative pressure and introduction of the gas G last throughout the kneading phase, the chamber being continuously maintained under negative pressure. 
     The method according to the invention can be applied to any kneading device whose chamber can be put under partial vacuum. It then suffices to add means of supplying gas to the said chamber.