Mixtures are known which are composed of a base powder which, for example, may comprise flour, sugar, raising agent (bicarbonate [s] and transformation acid [s]) and aromatic ingredients. In order to prepare the cake mixture the baker has to add to the powder a liquid (water or eggs for example) as well as a fat, before mixing it all, putting it into a tin and into the oven.

A recipe of this kind is not, however, always practical.

Mixtures are also known which are called complete, i. e. comprising the base powder, egg powder and a fat. But in these mixtures, the fat content has a very high melting point, for instance of the order of 50°C. In fact, with a fat having a low melting point, i. e. melting on the tongue, the mixture would lose its pulverulent quality and become pasty, with the result that starch grains of the flourwould be coated with paste, preventing their hydration when liquid is poured onto them, and thus would be baked in the oven without being hydrated, which would prevent them rising and would make the cake unintentionally sandy.

However, with such mixtures containing fat with a high melting point, the cakes which are obtained do not have a very satisfactory taste; they leave on the tongue, to use the expression of the person skilled in the art, a"filming"taste.

The applicant thus set itself the problem of preparing a mixture, for the preparation of a cake mixture, including a fat with a low melting point, but which would not make the mixture pasty and which would keep it pulverulent It is in these conditions that the invention is proposed which is a method of preparing a powder mixture for preparing a cake mixture by pouring on a liquid, the mixture comprising a base powder and a fat with a low melting point, characterised by the fact that -the fat is introduced into the base powder cold, -the fat is transformed into pieces and -the pieces of fat are mixed into the base powder cold.

Thanks to the invention, the fat is preserved in the mixture in a solid state, without being closely connected to the grains of the base powder. These grains are not coated; it is rather they which coat the individualized pieces of fat. This will anyway be the case as long as no mechanical force is applied to the mixture and even if the temperature increases slightly, up to 30°C for example. Before melting or becoming pasty, a fat becomes plastic but remains in the solid state.

Butter, for example, remains still relatively hard in the range from 20 to 25°C.

For the preparation of the cake mixture, it will be necessary to add to the mixture for example eggs, by way of liquid, and to beat the mixture. It will then be sufficient to pour the mixture into a tin and to let it bake in an oven to obtain the desired cake.

In the preferred implementation of the method of the invention, the fat is extruded cold to obtain filaments which are introduced into the base powder before being broken into pieces during the mixing.

The invention relates also to an extruderfor implementing the preparation method of the invention, characterised by the fact that the conformation and the density, at the surface of the exit extrusion grid, of the extrusion apertures are determined in order to reduce the heating of the fat through the grid.

It has been seen above that the base powder contains at least the following ingredients, moreover in relative proportions which can vary: -flour, -sugar, -raising agent (bicarbonate [s] and its [their] transformation acid [s]), -aromatic matter.

The transformation acid serves, during the pouring of the liquid, the necessary release of carbon dioxide. The raising agent is a bicarbonate (sodium, potassium,...) or a mixture of bicarbonates.

As fat, it is possible to envisage both vegetable and animal fats, but preferably butter. In a general manner, fats are considered which have a melting point lower than 37°C, advantageously lowerthan 32°C, or of which the melting point curve presents a low percentage of solid fraction at a temperature lower than 15°C.

The mixture also contains advantageously an antioxidant, to prevent the fat from going rancid.

By way of example, it will be noted that a mixture has actually been prepared containing -31 % dark chocolate with 58% cocoa, -2% powdered chocolate, -24% concentrated butter, -32.5888% sugar, -10% wheat flour, -0.1500% sodium bicarbonate, and 0.2500% pyrophosphate sodium acid (its transformation acid), -0.0112% ascorbylpalmitate (antioxidant).

In order, during the preparation and mixing, to keep the low temperature and thus to proceed cold, it is possible to incorporate carbon dioxide snow or liquid nitrogen, making the temperature inside the mixer drop to approximately 5 or 4°C, see below.

The annexed figures make it possible to understand better the implementation of the method of the invention: -figure I is a simplifie view of the installation for preparing the powder mixture, with its extruder and its mixer; -figure 2 is a plan view of the extrusion grid of the extruder, on a larger scale, and -figure 3 is a section view of the grid of figure 2.

The mixing installation comprises essentially a mixing tank1 and an extruder 2.

The tank 1, here with an axis 4 like a truncated cone, opening out upwards, comprises an endless screw 3 for raising and mixing and a mixing arm 5. The mixing arm 5 extends, in the upper portion of the tank, substantially perpendicular to the axis 4 and here radially between this axis 4 and the wall of the tank 1. During preparation, the arm 5 is driven in rotation around the axis 4.

The endless screw extends substantially parallel to the wall of the tank 1, here between a cardan coupling 11 at the base of the tank and the free end 12 of the arm 5.

During preparation, the Screw 3 is driven in rotation around itself and its upper end 13 is driven in a horizontal rotary movement with the free end 12 of the arm 5. The ingredients of the mixture (base powder and pieces of fat) are thus conveyed by the screw in an upward movement during the mixing and, by the screw and the mixing arm, in a horizontal rotary movement. By this double action of upward conveying and gyration, the ingredients are mixed gently and smoothly.

In the upper portion, the mixing tank 1 comprises a cover 6 provided with a hatch 7 for receiving fat, coming from the extruder 2 through a feed hopper 8.

The receiving hatch 7 is here off-center for a reason which will become apparent later.

The extruder 2 with its hydraulic pressurization unit 10, is perfectly standard apart from the exit extrusion grid 9, perforated, to a pre-determined density, by specific extrusion apertures 11 making extrusion possible in good conditions, practically without heating the fat.

Thus from a block of butter which is 0°C at its center, filaments of butter are extruded, the temperature of which does not exceed 5°C. In the case in point, the extrusion apertures 11 have a graduated cross-section, here narrowed at the top 12, towards the interior, widened towards the exterior 13, the widened detent section at the exit of the grid, being approximately 5 to 10 times as long as the narrowed section, here 9 times, for a thickness of extrusion grid of 20mm, in its narrowed portion, and of 3mm in its widened portion. As far as the density is concerned, in the internal portion of the grid, apertures, spaced out two by two, in two perpendicular directions, by one aperture diameter, correspond to a satisfactory density with regard to the cross-section of the extruded filaments and the heating of the grid. In other words, the conformation and the density, at the surface of the grid 9 of the extrusion apertures 11 are determined in order to reduce the heating of the fat through the grid.

It will be noted that the plasticity of certain fats could lead to reversing the direction of the extrusion apertures 11, with their narrowed section not at the top but at the bottom.

The extruded filaments enter by the off-centre hatch 7 of the tank.

Under the action of arm 5, screw 3 and of the other ingredients being mixed, stirred and raised, the filaments are cut into small pieces. It will be noted, however, that, in order to prevent accumulation of fat filaments on the mixing arm 5 and to safeguard the homogeneity of the mixture, the extrusion process is interrupted cyclically during periods of safeguarding (the homogeneity of the mixture), when the arm 5 arrives opposite the receiving hatch 7, thanks to which the mixture remains effectively relatively homogenous, without pieces of filament which are too long.

To resume the preparation method, in the mixing tank approximately 800 kg of base powder are prepared after 15 minutes of stirring. Then dry ice, or carbon dioxide snow, is added to lower the temperature of the mixture, then the stirring is carried out for a further 4 minutes approximately, the temperature of the mixture having dropped below 5°C.

Then the block of butter which is O°C is extruded to obtain filaments with a temperature which is also lower than 4°C and the whole is mixed for approximately one minute. It only remains to package the preparation, for example in 480g sachets.