METHOD AND APPARATUS FOR MIXING

Abstract: Apparatus for mixing dough comprises a dough mixer chamber 2 which has a lid 4. The chamber 2 is associated with a flour hopper l4 and also provided with a conduit 30 for oxygen-enriched air, a water inlet 22, and a vent pipe 26. In operation of the chamber 2, dough 6 is agitated by agitator l0 and a valve 42 in the conduit 30 is opened for chosen intervals of time to allow oxygen-enriched air to be passed into the chamber 2. During chosen time periods a valve 24 in the water inlet 22 is opened to enable at least that part of the conduit 30 proximate the chamber 2 to be flushed with water. Safe operation of the apparatus is thus made possible.

Description: This invention relates to a method and apparatus for mixing. In particular, it relates to the mixing of dough, a step in the manufacture of bread and like products. In the United Kingdom, much bread is made by the Chorleywood Bread Process. This process is described in publications of the FMBRA, for example, 'The Chorleywood Bread Process: the importance of air as a dough ingredient' (August 1977) N Chamberlain and T H Collins. In this process a dough comprising yeast, soya flour, fat and, if desired, emulsifier is inserted into a high-speed mixer. The dough is then mixed. The oxygen in the head space tends to undergo a reaction with an enzyme in the dough while the nitrogen remains unreacted, and forms bubbles in the dough which are subsequently expanded during the bread making process and are responsible for giving the baked bread its crumb structure. The dough typically also includes ascorbic acid and potassium bromate as bread improvers. Ascorbic acid is converted in the dough to dehydroascorbic acid as a result of a reaction with atmospheric oxygen in the presence of the flour enzyme ascorbic oxidase. Potassium bromate also acts as an oxidant and, if present in sufficient quantity, it is effective even in conditions where there is a scarcity of atmospheric oxygen. Typically, the dough is mixed for about 5 minutes employing a relatively high mixing speed. The head space of the mixer is then subjected to a partial vacuum so as to promote the formation of small gas bubbles in the dough. The dough may then be allowed to rest for up to 10 minutes and be proved for 30 minutes to an hour. It is then divided into desired shapes which are passed through a tunnel kiln and are baked in the kiln and then cooled. It has been reported that by performing the mixing of the dough in atmosphere comprising oxygen-enriched air, it is possible to use ascorbic acid as the sole improving agent, thus making it unnecessary to employ additives such as potassium bromate. Experiments demonstrating this result have been performed on a laboratory scale. However, there remains a need for a safe and reliable apparatus and method for using oxygen-enriched air in dough mixing on a commercial scale. This invention aims at providing apparatus and method that meet such need, particularly by flushing with water that part of an oxygen introduction conduit proximate a chamber in which the dough is mixed. It is also known to use oxygen-enriched air in other bread making processes. See FR-A-2 515 001 which discloses an apparatus for mixing dough including a closable dough mixing chamber, and separate valved conduits for introducing water, flour and other ingredients and oxygen-enriched air into the chamber to enable a dough to be formed in an oxygen-enriched atmosphere. According to the present invention there is provided apparatus for mixing dough, including a closable dough mixing chamber, a first conduit communicating at one end with the interior of the chamber and connectible to a source of oxygen or oxygen-enriched air, an automatically-operable valve in said first conduit whereby, in operation, the first conduit is able to be opened to the passage of oxygen or oxygen-enriched air into the interior of the chamber for chosen intervals of time, a second conduit communicating at one end with the interior of the chamber and connectible to a source of water, and an automatically-operable valve associated with said second conduit, whereby, in operation, the valve associated with second conduit may be opened to permit water to pass into the interior of the chamber for chosen periods of time, characterised in that the apparatus additionally includes a third conduit extending from a region of the second conduit upstream of the said automatically operable valve associated therewith and downstream of an additional automatically operable valve to a region of the first conduit downstream of the said automatically-operable valve associated with the first conduit, said additional valve being able to be opened so as to enable at least that part of said first conduit proximate the chamber to be flushed with water for chosen periods of time. The apparatus according to the invention may additionally include a vent pipe communicating at one end with the interior of the chamber and at its other end with the ambient atmosphere, and an automatically-operable valve in said vent pipe, whereby in operation the vent pipe may be open during chosen time periods. The apparatus according to the invention may additionally include a fourth conduit extending from a region of the second conduit downstream of said additional automatically-operable valve to the vent pipe whereby on opening said additional automatically-operable valve at least that part of the vent pipe proximate the chamber is able to be flushed with water. The apparatus according to the invention may additionally include a flour hopper having an outlet leading to the interior of the chamber and at least one automatically operable valve in said outlet whereby, in operation, flour may be passed into said chamber during chosen periods of time. The apparatus according to the invention may additionally include valve actuation control means, wherein said chamber has a lid, closure of which actuates a sensor to generate a signal to said control means and thereby to start a predetermined sequence of valve openings and closures. The control means may be arranged such that periods for which the valves in the first conduit and the vent pipe are open, are each insufficient for the composition of the gas in the head space of the chamber to become as rich in oxygen as said oxygen or oxygen-enriched air. The apparatus according to the invention may additionally include in at least one agitator in said chamber, and a variable speed motor for driving said agitator. The automatically-operable valve in said first conduit may be arranged to be open during at least part of the period in which said motor is operating at a relatively slow speed, or is adapted to be open only during periods in which said motor is not operating. The parts of the first conduit and the vent pipe which are flushed with water may have their internal surfaces formed of polytetrafluoroethylene. The invention also provides a method of mixing dough, including the steps of supplying oxygen or oxygen-enriched air through a first conduit to the interior of a mixer chamber so as to create in the chamber an atmosphere comprising oxygen-enriched air, introducing flour, water and other dough making ingredients into the interior of the mixing chamber, the water being supplied through a second conduit, and mixing the dough in the chamber in the presence of said atmosphere comprising oxygen-enriched air, characterised in that prior to the introduction of said oxygen or oxygen-enriched air into the chamber, at least that part of the first conduit proximate to the chamber is flushed by passing water from the second to the first conduit via a third conduit. We believe, that by employing an oxygen-enriched air atmosphere in the head space of the chamber, the atmosphere typically comprising from 40 to 60 per cent by volume of oxygen and from 60 to 40 per cent by volume of nitrogen, it is possible first to employ only ascorbic acid as an improving agent in the dough, and second to eliminate the need for a partial evacuation of the head space prior to mixing. Moreover, the apparatus according to the invention facilitates mixing under safe conditions and helps to prevent permanent accumulations of flour in the first conduit from arising. The method and apparatus according to the invention will now be described by way of example with reference to the accompanying drawings, in which : Figure 1 is a schematic diagram of a dough mixer, and Figure 2 is a schematic diagram illustrating a control circuit for the pneumatically - acutated ball valves employed in the apparatus shown in Figure 1. Referring to Figure 1 of the drawings, there is shown a dough mixer chamber 2 having a lid 4 and containing a mass 6 of ingredients which may be mixed to form a dough. The lid 4 shown in its closed position. There is a head space 8 above the surface of the mass 6 of ingredients in the mixer 2. The mixer 2 is provided with at least one agitator 10 driven by a suitable electric motor 12. The arrangement of agitator or agitators 10 and electric motor 12 may be the same as employed in the conventional dough mixers. Various means are provided in association with the lid 4 for feeding flour, water and oxygen-enriched air into the mixer chamber 2 and for venting gas from the head space 8 of the mixer chamber 2. These means include a hopper 14 for flour having an outlet 16 terminating in the lid 4. The outlet 16 is provided with automatically operable upper and lower butterfly valves 18 and 20, respectively. A water inlet conduit 22 also terminates in the lid 4. Pneumatically-actuated ball valves 24 and 46 are located in the conduit 22, the valve 46 being associated with the lid 4. A vent pipe 26 also terminates in the lid 4. Another pneumatically actuated ball valve 28 is disposed in the vent pipe 26. The vent pipe 26 has an outlet terminating in communication with the ambient atmosphere. The lid 4 is further provided with an inlet conduit 30 for oxygen-enriched air. In order to form the oxygen-enriched air, commercially pure oxygen is supplied from a source 32 thereof to a Witt gas proportioner or mixer 34 which mixes the oxygen with air to form a mixture of chosen composition. The mixer 34 and the source 32 of oxygen are typically located outside a room (not shown) in which the chamber 2 is located. The resulting mixture is supplied to a conduit 36 having a pneumatically-actuated ball valve 38 disposed therein and a manually operable flow control valve 40 disposed downstream of the valve 38. The conduit 36 terminates at its end remote from the gas mixer 34 in the oxygen-enriched air conduit 30. The conduit 30 has another pneumatically actuated ball valve 42 disposed therein. Extending from a region of the water inlet conduit 22 downstream of the valve 24 is a conduit 44 which terminates in the oxygen-enriched air conduit 30 downstream of the valve 42. Another conduit 48 terminates at one of its ends in the conduit 44 and at its other end in a region of the vent pipe 26 upstream of the valve 28. Opening the valve 24 thus places the conduits 44 and 48 in communication with the source of water (not shown) and enables the parts of the pipe 26 and conduit 30 nearest the lid 4 to be flushed with water. Each of the pneumatically-actuated ball valves 24, 28, 38, 42 and 46 has an associated pilot line. One such ball valve is indicated by the reference 90 in Figure 2 and the pilot line is indicated by the reference 92 therein. A solenoid valve 94 is located in the pilot line 92. The solenoid valve 94 is actuated either directly or indirectly as a result of closing the lid 4 of the mixer chamber 2 shown in Figure 1. Referring again to Figure 1, a sensor 52 is typically associated with the lid 4 such that a signal is generated on closure of the lid 4. Such signal is transmitted to a valve controller 56 which is adapted to open the solenoid valves associated with each one of ball valves 24, 28, 38, 42, and 46. The controller 56 is typically also operatively associated with a sensor 58 which is adapted to be engaged by the lower butterfly valve 20 of the flour hopper 12 when the valve 20 is in its closed position. The arrangement is such that the ball valves 38 and 42 cannot be open when the valves 20, 24 and 46 are open. The controller 56 is also employed to actuate the motor 12 that drives the agitator 10, although other means for actuating the motor 12 may be employed. The pipe 26 preferably has at least that portion thereof extending between the valve 28 and its end in the lid 4 formed of a flexible, stainless steel, braided, polytetrafluoroethylene (PTFE) internally-lined hose. Similarly, that part of the conduit 30 extending from the valve 42 to its end in the lid 4 is formed of such hose. Such hoses are safe to use with oxygen and have the advantage that they offer a low friction surface to any particles of flour entering their interiors, whereby such particles can be readily flushed therefrom by passage of water therethrough. Safe operation of the apparatus shown in Figures 1 and 2 is thus facilitated. The operation of the apparatus shown it Figures 1 and 2 to mix dough will now be described. With lid 4 of the chamber 2 open dough ingredients comprising fat, soya flour, yeast, ascorbic acid and, if desired, emulsifier are loaded into the interior of the mixer 2. The relative proportions of these ingredients may be selected in accordance with conventional practice for making bread by the Chorleywood Process. The lid 4 is then closed. A signal is thus generated and passed to the controller 56. The controller 56 thereupon provides signals opening the valves 18 and 20 to allow wheat flour to flow from the hopper 14 into the mixer 2. Simultaneously with the opening of the valves 18 and 20, the valves 24 and 46 are opened. As described with reference to Figure 2, the opening of the valves 24 and 46 is effected by opening solenoid valves associated therewith to apply a pneumatic pressure on valve members of the valves 24 and 46 in a valve-opening direction. The wheat flour employed in the operation of the apparatus may be of a kind conventionally used in making bread by the Chorleywood Process but will typically be unbleached and untreated. The relative proportions of wheat flour to water and other ingredients of dough may be as normally employed in the manufacture of bread by the Chorleywood Process. By opening the valves 24 and 46, water is caused to enter the interior of the mixer 2 mainly through the pipe 22 but also through the proximal ends of the pipe 26 and the conduit 30. The water is thus effective to flush flour and any particulate material from the pipe 26 and the conduit 30. Typically from 5 to 20 per cent of the total water flow into the chamber 2 is diverted through the pipe 26 and conduit 30. It is to be appreciated that the pipe 26 and conduit 30 will be arranged so as to avoid the creation of any internal volume in which water can be trapped. After a predetermined time, the controller 56 generates a signal effective to close the valves 18, 20, 24 and 46. On closure of the valve 20, a signal is generated by the sensor 58 and relayed to the controller 56. The controller 56 thereupon generates a signal to open the solenoid valves in the pilot lines associated with the valves 28, 38 and 42 thus opening these valves. An oxygen-air mixture, typically including 60 per cent by volume of oxygen, then flows into the pipe 30 and enters the head space 8 of the mixer 2 displacing air therefrom through the vent pipe 26. Supply of the oxygen-air mixture to the head space 8 is continued for a predetermined period of time, say, 20 seconds, this period being sufficient for the composition of the atmosphere in the head space 8 to assume substantially the same composition as the incoming air-oxygen mixture. The controller 56 then generates signals to close the valves 28, 38 and 42 and to start operation of the motor 12 so as to agitate and mix the dough therein. In the event that the motor 12 has a slow speed setting (or "star phase" as it is sometimes called) it is possible to start operation of the motor 12 and hence agitation of the mass 6 of ingredients simultaneously with the commencement of the supply of oxygen-air mixture to the head space 8, rather than at the termination of this supply. After an initial period of mixing, the speed of the motor 12 may be increased to a maximum and mixing of the dough continued at the maximum speed for a period of, say, 4 to 5 minutes. After a chosen period of time, the motor 12 may be de-actuated and mixing thus stopped. The dough may then be allowed to stand and prove, and after being removed from the mixer 2 may be divided into suitable shapes and passed into a kiln for baking in the normal manner. Typically, in the apparatus shown in Figure 1, as a safety measure, the valves 24, 38, 42 and 46 are all arranged so that in the event of a failure of, for example, pneumatic supply the valves remain in the closed position while the valve 28 in the vent pipe 26 is arranged contrariwise such that in the event of a failure of the pneumatic air supply, the valve remains in the open position. The apparatus shown in the drawings may be built to custom to mix dough. Alternatively, an existing dough mixer may be retro-fitted with an oxygen-air mixer and the necessary valves and pipes to operate in the manner described above. Various changes and modifications may be made to the apparatus shown in the drawings without departing from the invention. For example, instead of employing the mixer 34, to make an oxygen-air mixture, pure oxygen may be supplied from the conduit 36 to the pipe 30. In such an example of the invention, the period for which such pure oxygen is supplied is limited to that necessary to give an atmosphere of chosen composition in the head space 8 (for example oxygen-enriched air containing 60 per cent by volume of oxygen), i.e. for a period insufficient for all the air to be displaced from the head space 8. In addition, although it will be generally unnecessary to provide a partial evacuation of the head space immediately prior to the addition of oxygen or oxygen-enriched air to the head space, such a partial evacuation may, if desired, be performed. It is also possible for the period of oxygen introduction into the headspace to last for as long as the slow speed operation of the mixer or even to extend into the period of high speed operation of the mixer. If desired, a pressure sensor may be provided in the conduit 36 upstream of the valve 40 and arranged through the controller 56 to inhibit the start of the cycle of operations in the absence of oxygen pressure. Thus, it is possible to keep to a minimum the risk of mixing the dough in the absence of an oxygen-enriched atmosphere in the head space 8. By employing an oxygen-enriched air atmosphere in the head space 8 of the mixer 2, conversion of ascorbic acid in the dough to dehydroascorbic acid in the presence of the flour enzyme ascorbic oxidase is facilitated to the extent that it becomes unnecessary to add other oxygen-releasing improvers such as potassium bromate to the wheat flour. Typically, the ascorbic acid may be employed at a level in the order of 80 to 200 parts by weight per million of a wheat flour. As a result of the enhancement of the oxidising effect of the ascorbic acid, it becomes unnecessary to apply a partial vacuum as a means of improving the crumbed cell structure in the finished bread.

Claims: Apparatus for mixing dough, including a closable dough mixing chamber (2), a first conduit (30) communicating at one end with the interior of the chamber (2) and connectible to a source (32, 34) of oxygen or oxygen-enriched air, an automatically-operable valve (42) in said first conduit (30) whereby, in operation, the first conduit (30) is able to be opened to the passage of oxygen or oxygen-enriched air into the interior of the chamber for chosen intervals of time, a second conduit (22) communicating at one end with the interior of the chamber (2) and connectible to a source of water, and an automatically-operable valve (46) associated with said second conduit (22), whereby, in operation, the valve (46) associated with the second conduit (22) may be opened to permit water to pass into the interior of the chamber (2) for chosen periods of time, characterised in that the apparatus additionally includes a third conduit (44) extending from a region of the second conduit (22) upstream of the said automatically-operable valve (46) associated therewith and downstream of an additional automatically-operable valve (24) to a region of the first conduit (30) downstream of the said automatically-operable valve (42) associated with the first conduit (30), said additional valve (24) being able to be opened so as to enable at least that part of said first conduit (30) proximate the chamber (2) to be flushed with water for chosen periods of time. Apparatus as claimed in claim 1, additionally including a vent pipe (26) communicating at one end with the interior of the chamber (2) and at its other end with the ambient atmosphere, and an automatically-operable valve (28) in said vent pipe (26), whereby in operation the vent pipe may be open during chosen time periods. Apparatus as claimed in claim 2, additionally including a fourth conduit (48) extending from a region of the second conduit (22) downstream of said additional automatically-operable valve (24) to the vent pipe (26) whereby on opening the said additional automatically-operable valve (24) at least that part of the vent pipe (26) proximate the chamber (2) is able to be flushed with water. Apparatus as claimed in Claim 2 or Claim 3, additionally including a flour hopper (14) having an outlet (16) leading to the interior of the chamber (2), and at least one automatically operable valve (18, 20) in said outlet (16) whereby, in operation, flour may be passed into said chamber during chosen periods of time. Apparatus as claimed in any one of Claims 2 to 4, additionally including valve actuation control means (56), and wherein said chamber (2) has a lid (4), closure of which actuates a sensor (52) to generate a signal to said control means (56) and thereby to start a predetermined sequence of valve openings and closures. Apparatus as claimed in Claim 5, in which the control means (56) is arranged such that periods for which the valves (42, 28) in the first conduit (30) and the vent pipe (26) are open, are each insufficient for the composition of the gas in the head space (8) of the chamber (2) to become as rich in oxygen as said oxygen or oxygen-enriched air. Apparatus as claimed in any one of claims 2 to 6, in which there is at least one agitator (10) in said chamber (2), and a variable speed motor (12) for driving said agitator (10), and said valve (42) in said first conduit (30) is arranged to be open during at least part of the period in which said motor (12) is operating at a relatively slow speed, or is adapted to be open only during periods in which said motor (12) is not operating. Apparatus as claimed in any one of claims 2 to 7, in which said parts of the first conduit (30) and the vent pipe (26) have their internal surfaces formed of polytetrafluoroethylene. A method of mixing dough, including the steps of supplying oxygen or oxygen-enriched air through a first conduit to the interior of a mixer chamber so as to create in the chamber an atmosphere comprising oxygen-enriched air, introducing flour, water and other dough making ingredients into the interior of the mixing chamber, the water being supplied through a second conduit, and mixing the dough in the chamber in the presence of said atmosphere comprising oxygen-enriched air, characterised in that prior to the introduction of said oxygen or oxygen-enriched air into the chamber, at least that part of the first conduit proximate to the chamber is flushed by passing water from the second to the first conduit via a third conduit.

Inventors: BOOKER, PAUL IAN, LEESON, RICHARD HARVEY
Applicants: THE BOC GROUP PLC
Application year: 1987
Main classification: A21C1
IPC codes: A21D8, A21C1