Dough Mixing for Farinaceous Foodstuff Production

For many years attention has been directed in the bakery industry to the production of so-called "no-time" doughs, which may be generally defined as a dough which is not a sponge, but which does not require any or any substantial fermentation in bulk. The achievement of a satisfactory "no time" dough production method is an obvious desideratum, because bulk fermentation is one of the most time consuming steps in the breadmaking process.

As long ago as 1937 Baker and Mize (then of Novadel-Agene Corporation of Newark, N.J., U.S.A.) showed in a paper entitled "Mixing doughs in vacuum and in the presence of various gases" (published in "Cereal Chemistry, Vol. 14" page 721) that the texture of bread was largely influenced by the gas cells present in the dough. In another paper the same authors (then with Wallace and Tierman Laboratories of Newark) showed that the gas cells were all present after dough mixing and that "no-time" doughs could be made using oxidising agents. ("The origin of the gas cell in bread dough" Baker and Mize published in "Cereal Chemistry, Vol. 18, January 1941" at pages 19 to 33). This paper contains the interesting statement:

"The bread obtained by this no-time process is nearly identical to that obtained by the use of bromate in a two or three-hour straight dough process. The main difference is in the flavor."

The statement is interesting because subsequent attempts to make satisfactory "no-time" bread doughs on a commercial scale have been beset by two basic problems, namely (i) texture of the bread-i.e. distribution of the gas cells, and (ii) loss of flavour.

In England, successful production of no-time dough was achieved by the Flour Milling and Baking Research Association at Chorleywood in 1961 and it was shown that the process was essentially controlled by the energy input to the dough during mixing which has to be approximately 11 watt hours per kilogramme weight of the total ingredients and that this energy must be added within five minutes. (See Report No: 59 of the British Baking Industries Research Association, Chorleywood). This is referred to hereinafter as "the Chorleywood Bread Process".

Even with the Chorleywood Bread Process problems of texture still arose in connection with the type of bread marketed by large bakeries in England in 1962, and it was eventually found to be necessary to mix the dough under vacuum conditions to meet the texture requirements of the market. (See British Pat. No: 1,035,314--K. Pickles).

Attempts to use the Chorleywood Bread Process in the production of relatively low density soft bread such as that commonly produced by the medium and large sized bakeries in the United States of America have not hitherto proved successful. The present invention however provides a process for the production of no-time doughs for soft bread which has proved successful in the manufacture of bread which would be acceptable commercially in, for instance the U.S.A.

It is to be noted here that once a particular bread of given characteristics, density, texture, flavour, colour and the like, has come to be accepted in a particular large scale market, it is not then commercially acceptable to have any substantial variation of any of these characteristics. It is generally accepted by the bakery industry in the developed countries, that the cost of educating the public to purchase and eat a bread with a different characteristic is many times that required to achieve the known, and accepted characteristics by technical changes in the production techniques. Therefore, success in this field is measured by the degree to which the characteristics of the bread produced by known methods can be reproduced.

Reference has been made above to bread as produced in the U.S.A. For the purpose of this Specification such a bread can be defined as:

(a) bread made from the following essential ingredients in substantially the proportions indicated (percentages are by weight):

and (b) having a specific volume of 4.5 to 7.00 cubic centimeters per gramme.

It is to be understood that the invention is not restricted to the production of bread of the kind which is consumed in the United States of America. There is evidence that the invention can be used to produce bread and other baked farinaceous foodstuffs of very good texture and flavour but suited to the market in other countries (e.g. the United Kingdom, Germany, Australia).

According to this invention a method of dough mixing for the production of farinaceous foodstuffs of the type in which the energy added during mixing is sufficient to substantially determine the cell structure of the finished product, and in which the dough (not being a sponge) requires substantially no fermentation in bulk, is characterised by the facts that: the energy added during mixing in a chamber is not less than 15 watt hours per kilogramme of the total dough ingredients; the rate of energy input is such that this energy is added in not more than 7 minutes; the process is regulated by passing a fluid coolant through a jacket surrounding the mixing chamber so that the temperature of the dough mass after mechanical treatment is within the range 25.degree. C. to 25.degree. C., and at least one of the ingredients sugar and fat is added part way through the mixing process.

Experience of the Chorleywood Bread Process in the production of English bread has shown that it is not necessary to vary the total energy input from the 11 watt hours per kilogramme figure by more than a few percent, and indeed the baker would attempt to keep the energy input to as low a figure as possible. Hence when work commenced on the mixing of American type dough, it was not thought possible to make any substantial alteration in the total energy input, and even when experiments to increase energy input were made, these were initially only small increases showing no significant advantage. It was surprisingly found that one of the factors in achieving success, was the addition of a much higher energy input than 11 watt hours per kilogramme of the ingredients, during the mixing process, and 15 watt hours was identified as the lower limit of success. However, at the new, very much increased energy input, a further problem immediately presented itself, because the temperature of the dough rises during mixing (the absorbed energy appearing largely as sensible heat) and the subsequent processes could not be controlled if the temperature of the dough at the end of the mixing was greater than 35.degree. C. It is possible to pre-cool the water, but in warm climatic conditions experienced in certain states of America, and certain other countries, this pre-cooling of the water is not sufficient by itself, because even if the water is chilled so that its temperature as fed into the mixing chamber can be considered to be approximately 0.degree. C., its mass is not adequate to produce the required temperature limitation on all the ingredients. This problem of temperature rise occurs because of the very high rate of energy input. An acceptable product was only achieved when the new high level work input was combined with the cooling of the walls of the mixing chamber by passing a fluid coolant through a jacket surrounding the mixing chamber. The work up to this point had been carried out by the present inventor jointly with Thomas Hylton Collins and is the subject of International Patent Application PCT/GB/79/00153 (U.S. patent application Ser. No. 194,291, filed May 15, 1980. Further work by the present inventor has led to the surprising and to some extent inexplicable discovery, that even better results are achieved (or the same results can be achieved more easily) if the ingredients sugar and/or fats are added part way through the mixing process. Preferably, the sugar and/or the fat are added after at least 25% of the total mixing time in the mixing chamber.

It has further been discovered by the present inventor that the coolant should preferably be a liquid having a freezing point lower than that of water and the coolant is at a temperature of less than 0.degree. C. For instance, the coolant may comprise ethylene glycol or a halogenated hydrocarbon (FREON).

It may be desirable to pre-cool at least some of the dry ingredients before development in the mixer commences. This may be achieved, for instance, by placing the flour and other dry ingredients in the mixing chamber and operating the agitator. This has the effect of swirling the ingredients in the atmosphere inside the chamber, which is much the same as flowing an air stream through the ingredients.

According to a preferred feature of the invention, at least part of the mixing (and preferably substantially the entire mixing) is carried out under vacuum conditions-i.e. less than atmospheric pressure. In fact, it may be desirable to subject the ingredients to a reduced pressure before commencing mixing. The pressure in the mixing chamber may be reduced to between 550 TORR and 250 TORR.

One form of mixing apparatus suitable for carrying out the process of the invention and its method of use will now be described by way of example only with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of a mixing machine,

FIG. 2 is a front view of the mixing machine shown in FIG. 1, with a portion broken away,

FIG. 3 is a cross-sectional view taken along the line A--A of FIG. 4, showing a mixing chamber which is a portion of the mixing machine,

FIG. 4 is a side view of the mixing chamber shown in FIG. 3,

FIG. 5 is a top view of a rotary mixing device,

FIGS. 6 and 7 are side views of the device shown in FIG. 5,

FIG. 8 is a front view of a vertical blade member as viewed along the direction of the arrow A in FIG. 5,

and

FIG. 9 is a side view of the upper portion of a vertical shaft 13 as viewed in the direction of the arrow B of FIG. 5.

FIGS. 1 and 2 shows the overall arrangement of a mixing machine suitable for dough mixing according to the present invention. A mixing chamber 2 is supported by a machine frame 1, supported on bearing stands 4 and 5, there being journal bearings 4a located at each end of the frame. A mixing device 10 which will be hereinafter described in detail is located within the mixing chamber 2, and power for driving the mixing device 10 is provided by a motor 3, the drive being transmitted through a pulley 7a, a belt 9, and a wheel 8. The device 10 is supported by a bearing assembly 6, located directly below the centre of the chamber 2, so that it is adapted to rotate about a vertical axis. The machine also includes a ram-and-cylinder device C, which is adapted to tilt the entire frame 1 when the dough is to be discharged from the chamber 2 upon completion of a mixing and kneading operation.

FIGS. 3 and 4 illustrate the mixing chamber 2 in detail. The chamber has the form of an open-topped cylinder and comprises an inner shell 20 and a bottom wall 21, and is surrounded by a jacket 22 which is defined by the inner shell 20 and an outer shell 25, the jacket being enclosed within a heat insulating cylindrical mantle 24 accommodating a heat insulator 26. Baffle plates 28 extending axially of the chamber 2 are welded inside the jacket 22 between the inner and outer shells. A fluid inlet 30 and a fluid outlet 32 are provided in the outer shell 25 and alternate baffle plates extend, one from the bottom of the jacket to a position near to the top of the jacket (leaving a gap above the baffle plate and below the top of the jacket) and the other from the top of the jacket to a position near to the bottom (leaving a gap below the baffle plate and above the bottom of the jacket). If a temperature regulating fluid for cooling or heating is introduced into the jacket through the fluid inlet 30, the fluid will initially rise within the jacket and proceed from a gap at the upper portion of the jacket to a neighbouring compartment in which the fluid will descend, thereby allowing the fluid to flow uniformly up and down in regular succession within the jacket before finally being discharged from the fluid outlet 32. Designated at 31 is a drain port for attaching a drain cock. In this particular construction only the baffle plate between the inlet 30 and the outlet 32 is welded along both its side edges 27 and upper and lower ends so as to form a fluid-tight seal between the inlet 30 and the outlet 32. It is to be noted that the fluid is compelled to travel over an undulating path which is almost the full depth of the chamber 2.

FIGS. 5 to 9 depict a more detailed view of the rotary mixing device 10, which as shown, is mounted in the bottom portion of the mixing chamber 2. As illustrated in these drawings, a centre disc 15 having a vertical shaft 13 upstanding at its centre is secured to an approximately octagonally shaped rotary plate 11. Projecting outwardly from the upper part of the vertical shaft 13 and approximately perpendicular thereto is an arm 12a to which is fixed the upper portion of a mixing vane 12. The lower portion of the mixing vane 12 is fixed to a vertical blade member 14 upstanding from the centre disc 15. There may be provided a plurality of reinforcing ribs 17a on the lower face of the rotary plate 11, if necessary.

As can be more clearly seen in FIGS. 6 and 7, the mixing vane 12 in its upper portion points in the forward direction of rotation and has a wing-shaped configuration, the vane also including a curved portion which points downwardly. Arranged about the outer circumferential portion of the rotary plate 11 and spaced apart from each other substantially equi-angularly are a plurality of scraping vanes each composed of a circumferentially directed vertically extending small square plate or vane member 17, a small rectangular scraping vane member 18 fixed to a mounting 18a formed by bending down the edge portion of the rotary plate 11, and a scraping vane member 19 obtained by leaving the mounting plate 18a uncovered. The angle defined by the upper end of the vertical blade 14 and the plane of the mixing vane 12 is preferably about 45.degree. as shown in FIG. 8, whilst the angle defined by the arm 12a and a line perpendicular to the axis of the vertical shaft 13 is preferably in the order of 60.degree. as shown in FIG. 9. However, the magnitudes of these angles are not critical.

In the preparation of a bakery dough, the ingredients are placed in the mixing chamber 2, and are first pressed downwardly by the surface of the kneading vane 12, upon rotating the member 10 in the direction of the arrow as shown in FIG. 5. Since the vertical blade member 14 extends from the bottom surface of the vane 12 and points substantially in the direction of rotation, the dough which has been pressed down below the vane 12 is sectioned and then divided (cut and folded) on either side of the vertical blade member 14. In this way, the portion of the highly viscous dough that has been thrust radially outwards from the rotary member 10 is pulled and folded by the vertical vane member 17. Meanwhile the portion of the dough located closer to the centre of the tub is gradually thrust radially outwards while colliding with and piling on the portion pulled and folded as described above. The dough as it approaches the outer periphery of the rotary member is scraped up and down by the scraping vane members 18,19 whilst being pressed between the deflecting member 23. However, just as the dough is being lifted it is once again pressed down and turned under by the mixing vane 12, after which the vertical blade 14 again sections the dough, so that the pulling, folding, colliding, piling, and scraping operations are repeated. Since the dough is thus repeatedly subjected to stretching and cutting actions resulting from a combination of powerful movements, the mixing, stirring and kneading operations are rapidly and uniformly carried out, thereby allowing complete mixing and kneading of the dough in a short period of time. Moreover, because of the various cutting and folding actions which take place for every revolution of the device 10, it is feasible to add a relatively large amount of energy to the dough in a short period.

The mixing chamber 2 is fitted with a lid (not shown) which is adpated to seal on to the rim of the chamber and there is also provided pumping means (not shown) for evacuating air from the interior of the chamber 2 when the lid is in the closed, sealing, position. An inlet valve is provided in the lid through which liquid ingredients such as liquid fats and sugar can be fed into the chamber 2 after the lid has been closed and part way through a mixing operation if desired.

By using a mixing machine of the type shown in the drawings, it is possible to produce a dough which has attained a highly developed glutinous state in a very short period of time. The air bubbles entrapped within the dough are dispersed and distributed finely and uniformly, and the dough exhibits excellent mechanical tolerance, namely resistance against breakage of the gluten network. In effect, it is possible to produce dough which has had sufficient energy added to it in the mixing machine, to determine the final cell structure of the finished baked product, and it is possible to avoid the conventional bulk fermentation step, which in some cases could take as long as four hours.

During a dough mixing process in the chamber 2, the dough temperature rises in proportion to the energy input, and if permitted to rise without control, the temperature would soon attain a level at which the dough could not be successfully turned into an acceptable product. However, the presence of cooling liquid in the jacket 22 retards the temperature rise of the ingredients, and consequently it is possible to avoid raising the dough to a temperature too high for subsequent processing. Obviously, chilled water could be used in the jacket 22, but in some instances, it is preferable to use ethylene glycol, or a halogenated hydrocarbon, which has a freezing point lower than that of water, so that the liquid coolant being pumped through the jacket, can be at a temperature less than 0. .degree.C.

By use of this temperature control, it is possible to produce good dough in conditions where the ambient temperature is such that without the use of the jacket cooling method, it would be impossible to add the necessary energy to the dough in the mixer without overheating the dough. It is important that the cooling liquid should circulate vertically by approximately the depth of the rotary member 10, to ensure that the cooling effect of the jacket is adequate.

Hamburger buns of the type commonly marketed in the United States of America were produced, having the following formulation:

The flour at a temperature of approximately 21.degree. C. was placed in the mixing chamber 2 of a machine of the type described above with reference to the drawings, and to the flour were added the yeast in suspension, the dry ingredients and the remainder of the water. The water was supplied at a temperature of approximately 4.degree. C., except for 0.5 kilogrammes which was supplied as ice. The sugar and fat were not added at this stage. The mixing machine was then operated to mix the ingredients in the chamber by the method previously described, and at the same time air was evacuated from the chamber by the vacuum pumping system, down to a pressure of approximately 265 TORR.

When the machine had been in operation for 55 seconds, about 5 watt hours per kilogramme of the total dough ingredients had been added to the dough then forming in the mixing chamber. At that stage, the sugar and fat were added through the valve in the lid, and this necessitated breaking the vacuum. However, the addition of the sugar and fat took only a few seconds and then the valve was closed and the pressure again dropped to about 265 TORR. Mixing was then continued to a total time of about 3 minutes 50 seconds and by then approximately 21 watt hours per kilogramme of total dough ingredients had been added and the dough was fully mixed. The temperature of the dough at the end of mixing was about 31.5.degree. C. and this is acceptable.

Throughout the mixing process ethylene glycol was passed through the water jacket 22 of the mixer at a pressure of approximately 0.7 kilogrammes per square centimeter and at a temperature of -6.7.degree. C.

After mixing, the support frame 1 was tilted, and the dough dropped into a conventional hamburger bun trough, in which it was wheeled the length of the dough room at an ambient temperature of 16.degree. C. to 21.degree. C., before being dropped into the divider hopper. The transferring operation took approximately 3 minutes. The total quantity of dough (85 kilogrammes in the particular example) was then worked off through a dough moulder and panner into 4 inch hamburger buns which scaled at 0.82 kilogrammes per dozen. After leaving the panner, the buns were subjected to a conventional proving in a static proof box at 43.degree. C. to 46.degree. C. with 90% relative humidity. The proving time was 45 minutes.

The buns were then baked at 180.degree. C. for 71/2 to 8 minutes. The baking time could be varied of course, but the market which was being supplied by the particular test batch prefers a slightly pale bun. Following baking, the buns were cooled for 17 minutes and then sliced on a standard band slicer.

American bread was manufactured using a dough mixer of the kind shown in the drawings, the bread having the following formulation:

The quality of the bread was considered to be fully comparable with commercial American white bread.

It will be appreciated, that the above described examples are but specific instances of the manner in which the invention can be used. Obviously, different formulations can be used for different types of end product, and the procedure will be varied accordingly.