Sheeting and cutting in biscuit processing is the most popular way of forming pieces of dough from fermented or developed dough, and in some instances for the short dough.
The sheeter compacts and gauges the dough mass into a sheet that is of even thickness and at the full width of the plant. It is important to ensure that there are no significant holes and that the edges are not ragged but smooth. In most cases, the sheeter will also allow for the incorporation of dough that is returned to the cutter, referred to as scrap, with virgin or fresh dough received from the mixer. The dough is compressed within the sheeter and worked over thereby allowing for the removal of air. During this process, certain stresses will also be inevitably built up in the gluten structure.
The new dough sheet will then pass into one or more sets of gauge roll pairs, which are designed to reduce the thickness that is required for the dough cutting. The dough is typically carried on conveyors between the sheeter and each of the gauge rolls. In certain instances, when the thickness of the dough has been reduced, the sheet is then folded to form many laminations before it is further gauged into the final thickness that is desired. It is important to note that as the dough sheet becomes thinner as it progresses to the cutter from the sheeter, it subsequently becomes longer. As such, every gauge roll and subsequent conveyor will run faster than the ones before it.
The thickness of the dough is gradually reduced by pairs of heavy steel rolls to the level that is desired for cutting. There are typically 2-3 pairs of rolls, although a single pair may be used for short dough, while a minimum of three for instances that require very gentle reductions. The rule of thumb for thickness reduction at each gauge roll is 2:1, although ratios of up to 4:1 are commonly used as well. Clearly, the higher the ratio, the more stress and work that will be put into the dough.
In most cases the pair of gauge rolls are vertically mounted, one above the other. To adjust the gap, you would need to move one roll, sometimes the lower and other times the upper one. All gauge rolls have instruments that indicate the gap setting. This allows for the changing of the machine, as well as the recording of settings with greater accuracy. Gauges will often not correspond well with the gap, although this is a simple case of engineering maintenance for calibration.
When the dough emerges from the gauge roll, it is typically of a thickness that is slightly greater than the gap that it came through. This is as a result of the dough’s elastic properties, as well as due to the fact that some extrusion occurs through the nip, in comparison with rolling.
The cutting phase is designed to produce the outline of the desired size and shape for your biscuits or cookies. It is therefore important to ensure that the piece of dough adheres to the cutting web and not to the cutter. However, this adherence should not be too severe otherwise the baker will experience problems as they attempt to transfer the pieces, without distortion, onto the oven band or even the next conveyor.
Cutters are used to stamp out one or multiple rows of biscuit or cookie pieces at a go. The equipment used is typically strong and incorporates a swinging mechanism. In this way, the dough sheet is able to move at a constant speed, while the cutter drops, travels with the dough, then rises and swings back before it drops once again. Adjustments may be made to allow for light or heavier cutting with the falling of the block.
Where simple cutting is required, the cutter drops onto the dough and the ejector plate is then pushed back. As the cutter lifts away, the ejector pushes the dough, thereby ensuring that it remains on the cutting web without sticking to the cutter. Some dough sheet thickening may occur before cutting as the dough relaxes. In such a case, take care to avoid excessive cutting pressure by the initial cutting rolls that could displace the dough into the scrap thereby producing lighter dough.
The cutting machine refers to the entire machine series including the sheeter, cutter and panner which finally places the pieces of dough into the oven band.
The sheeter is designed to create a consistent sheet of dough that becomes ready for further reduction or dough forming. Powered rolls rotate toward one another, drawing unprocessed dough from the hopper. The ideal sheet thickness produced is controlled by the distance between the rolls. Adjustment for this gap may be carried out during biscuit or cookie production, thereby accommodating the type of dough, as well as the needs of the downstream equipment. The dough is compressed into a single sheet by the rolls, thereby producing consistent thickness and characteristics. Rolls are manufactured to exacting concentricity tolerances, thereby allowing for the maintenance of consistent formation of the dough sheets.
Cutters are designed for the uniform cutting of biscuits before baking. The accurate cutting controls enable the baker to create various product sizes with a simple press of a button. Cutters may be integrated into an existing production control and frame system, or built as standalone machines. Precise control of the speeds of the various conveyors and machines is vital to ensure that the cutter runs smoothly to produce the appropriate size and shape of biscuits and cookies.
Potential Problems and Solutions
• Oddly Shaped Biscuit or Cookie – At each gauging station, extra stress is added to the dough sheet. There is usually insufficient time for the complete relief of such stresses before reaching the next processing stage. The manner in which the dough sheet is fed into the gauge roll will impact the amount of stress that is placed upon the dough. It is therefore important to take care and apply precise control where necessary. This will enable you to avoid variable stresses that typically persist all the way to the cutter and may thereafter alter the shape of the baked cookie or biscuit.
• Dough Sticks on Cutter – In the event that the dough repeatedly sticks to the cutter, this is a clear problem with the dough consistency that has been taken for cutting. Such a case would require that the dough sheet is lightly dusted with flour. Alternatively, a little drying of the dough sheet may be effected with a blast of air before the cutting process is begun.