Principles and techniques of laminating
The purpose of laminating is to build up a layered structure by rolling the dough then folding it and turning it through 90° at least once before gauging to the final thickness for cutting. This develops the gluten and gives a delicate flaky structure in the baked biscuit. In many cases another material, such as fat, is introduced between the layers to encourage further separation of the layers during baking. Originally laminating was done manually using a reversing brake but now automatic laminators are used.
Dough lamination is now used principally for cream cracker and puff doughs but any developed (hard) dough can be laminated with benefit. If semisweet or savoury cracker doughs are made using sodium metabisulphite or enzyme to modify the gluten, it is not necessary to laminate, as straight sheeting and gauging will produce satisfactory biscuits.
Cream cracker dough has a bread type recipe and is fermented with yeast. It is difficult to sheet smoothly but it is usually laminated not only to create a clearer dough but also to allow the introduction of flour and fat mixture ("cracker filling dust") designed to keep the dough layers separated a little during baking. The fact that some cream cracker manufacturers use very little "cracker dust" tends to show that it is the dough sheet/stress relieving function of the laminator that is of most importance to the biscuit structure.
By introducing a lot of fat between the dough layers a very flaky structure is produced and this is the characteristic feature of puff biscuits. The fat may be introduced as knobs into the dough prior to sheeting, or as a continuous layer after a good dough sheet has been formed. In either case, gauging and laminating is needed subsequently to build up the number of dough layers which appear as very thin flakes in the baked biscuit or pastry.
A critical feature of puff dough production is the plasticity of the fat or fat/flour mixture that is used. It is necessary for the consistency of the fat and dough to be very similar so that the fat does not break through the dough layer or, alternatively, squeeze out. In order that the fat used does not have a large high melting point tail above body temperature but is sufficiently firm and plastic in consistency it is normal to arrange that the dough is cold, usually not more that 18°C.
Types of Laminator
The following types of automatic laminator can be identified:
1. Vertical with continuous lapper and one sheeter. This usually is composed of a three roll sheeter with cutter scrap incorporation, two or three gauge rolls, cracker dust spreader on part of the sheet and a zig-zag lapper capable of building up about 10 or 12 layers. The advantage of this type of laminator is the continuous smooth action of most parts, but the disadvantages are:
- There are stresses introduced in the laminated dough at the edges due to folds.
- The exposure of top and bottom of the sheet on successive Vs of the folded dough (this can mean that the scrap dough is alternately exposed if incorporated in one side of the sheeter).
- The cracker duster is intermittent in action and must be synchronised with the lapper. Also the filling dust is normally only between every other lamination.
2. Vertical with continuous lapper but with two sheeters. Here two-roll sheeters make sheets and filling dust is incorporated prior to subsequent gauging. The advantage of this type would appear to be that the filling can be spread continuously over the full width of the sheet, but disadvantages are the same as for the previous type of laminator combined with the fact that by using two roll sheeters, poor sheets may be formed and it is these sheets that have to "hold" the filling.
3. Horizontal laminators (see below). These are similar in performance to the vertical types, but the sheeting and gauging (also the cracker dust filling) occurs on units spread out horizontally before the lapper, more like conventional biscuit cutting machines. The disadvantage of this type is that the whole machine takes a lot of floor space because a right angle bend in the line of plant is required where the lapper is sited. The advantage is that more than one lapper can be used if required, introducing a second "turn" to the dough. It is usual to use two three roll sheeters in horizontal laminator systems and cracker dust or more fatty fillings can be added between the two sheets (that is, on the lower sheet of dough).
4. Cut sheet laminators. Both the vertical and horizontal laminators described above are of the continuous sheet folded type, but either can be supplied with a cut sheet lapper. This means that a dough sheet is laid down only as the lapper retracts; it is only the top of the dough sheet that appears on the pile of laminated dough. The advantages are that little or no stress is involved at the edges since no folding occurs and also that an in-line laminating arrangement is an option. The disadvantages are a more complicated laminating action is needed to cut and lay down the sheets, and cut edges may expose the filling onto the subsequent surface of the dough. This is particularly important where a heavy fat filling is involved.
The vertical laminators were introduced to save floor space and by reducing or eliminating canvas webs between gauge rolls much machinery was saved. However, machining dough involves stresses in the gluten network and these stresses can only be relieved with time. The close proximity of the components in the vertical laminators allows much less time for natural stress relief than the horizontal configurations. Various types of vertical laminators have been designed with resting webs between gauging stations. These machines start to approach the complexity and costs of the horizontal types.
In all laminators the width of the laminated pile of dough can be controlled by attention to the length of the stroke of the laminating section and the number of layers formed can be altered by adjusting the relative speed of the conveyor that takes away the laminated dough. The faster that this conveyor runs the fewer the number of layers.
Process control during laminating
As the lapper builds up the layers of dough it is important to make speed adjustments so that exactly the same number of laps is present at all times. If a variable thickness occurs, the feed to the next gauge roll will be uneven and irregular stresses will be set up in the dough on gauging to a final thickness. The best check on whether the laps are placed correctly is to observe the dough as it emerges from the next gauge roll. If it shows bands of crushed or stretched dough associated with the edges of each lap, appropriate opening or closing of the space between each lap can be made by changing the speed of the laminator relative to the laminated dough web.
It is quite important for the quality and shape control of the baked biscuit that the amount of filling introduced between the laminations is uniform. Malfunctioning of the filling duster will result in uneven weights and lift of biscuits and may be enough to affect the colouration and eating qualities also.
The number of laminations required to give an optimum quality of biscuit should be decided by experiment. Too few laminations will give a ragged flaky structured biscuit that may split open along the lines of the laminations and too many will result in excessive crushing during gauging prior to cutting leading to a biscuit that has poor thickness development. The latter effect can be reduced if a thinner dough sheet is laminated.
Poor quality edge-lane biscuits are often observed in laminated products. Careful observations at the gauging after the laminator will usually indicate the reasons. If, for example, the width of the laminated dough is too great, crushing will be occurring at the edges; if too narrow, some pulling will be apparent. It is simple to make adjustment to the length of the stroke of the laminator carriage.