Sandwich Biscuits: From Cream Application to Cooling of Creamed Sandwiches
Methods of cream application
The operation of biscuit cream sandwiching was originally entirely manual involving the stencilling of the cream onto a base followed by the addition of a top. The stencil was cut in a metal sheet of a thickness appropriate to the thickness of the cream required and the shape of the stencil was appropriate to the size of the base biscuit. The base biscuit was located under the stencil hole, the cream was filled and smoothed into the hole either with a palette knife or from a swinging hopper and the biscuit was then taken away with the cream adhering (see Fig. 1). The stencil plate was maintained at a temperature slightly higher than the cream to reduce preferential sticking of the cream to it. The cream needed to be fairly fluid but rigid enough to maintain shape as the biscuit was withdrawn from the stencil plate.
Fig 1: Sequence for forming a cream sandwich by extrusion and wire cutting
This system was mechanised and creaming machines are still sold which operate on the stencil principle. They are usually intermittent in action allowing location of the biscuit beneath the stencil, filling of the stencil hole and then removal of the biscuit to a ‘topping’ station where the top biscuit is pressed on to make the sandwich. Although this type of machine is relatively slow in action, the system allows a second deposit such as jam to be applied on the precisely located biscuits. Stencilling requires a fairly fat rich cream to maintain the desired fluidity. As the stencil plate thickness is fixed the only means of weight control is by changing the density of the cream. This is not easily achieved with most mixing equipment.
The second method of cream application is by means of multi-nozzled depositors of the cake batter type. The depositor head may lower and travel with the biscuit in a continuous motion or the head may be fixed and the biscuits moved intermittently.
This system relies on the deposit breaking away from the nozzle as the latter is raised so the cream must be quite fluid and the biscuit relatively heavy if clean operation is to be achieved. Suction systems have been devised to hold the biscuits down where necessary, but this is an engineering complication. The topping arrangement is similar to that for the stencilling machine. Alternatively, rows of biscuits are presented to the depositor head in such a way that cream is placed on alternate rows and a suction mechanism picks up the other rows and places them onto the creamed bases. This is the arrangement for the Cookie Capper machines and others like them. Clearly, the biscuits in the rows for receiving the cream have to be inverted and those used for the tops are not.
Fig 2: Capper Tronic
Stencilling and depositing machines usually require the presentation of biscuits in rows on a conveyor up to one metre wide. Although this arrangement is possible as an inline system (as for the Cookie Capper machines), it is usual to feed the biscuits from magazines providing the appropriate number of lanes. These magazines are hand filled and an exactly similar magazine is required to provide the biscuits for the tops of the sandwiches. Speeds of up to 45 and 60 rows per minute are typical for stencilling and depositing machines respectively. The wide (row type) arrangement is ideal for cooling and subsequent presentation to a chocolate enrober.
In order to handle stiffer (lower fat content creams) and to increase production speeds, there was a development of extruded and wire cutting machines to meter and deposit the cream. Although the systems are sometimes referred to as stencilling, this is not accurate and there is a clear difference from the true stencilling arrangements. Cream from a hopper is pushed out of a nozzle of appropriate shape, the cream is located onto the biscuit base and it is then severed from the nozzle with a taut wire. Machines of this type operate on a continuous motion which extracts a biscuit from a magazine feed onto a pinned chain. The biscuit is transported under a rotating nozzle arrangement such that as a nozzle and biscuit coincide there is an extrusion of cream which presses onto the biscuit and is then cut off with the wire. The creamed base moves onwards to a topping station where the pin pushing the biscuit extracts a top biscuit and the two are pressed together under a wedge or roller.
Most machines of this type are based on the original designs by the Peters and Quality companies of the USA. They apply cream onto only one to four lanes of biscuits, but at speeds of up to 800 biscuits per minute per lane. Lane multiplication devices allow a doubling, or more, of the number of lanes after they leave the machine for the purposes of biscuit cooling. Penny stacking can be arranged onto the cooling conveyor. It will be appreciated, however, that this arrangement means that longer narrower cooling conveyors are required than those that follow the stencil type machines.
A major problem of these high-speed machines is the potential damage to the biscuit shells as they are stripped from the magazine feeders onto the chains that carry them under the cream depositing position. Normally the stripping is by pairs of pins fixed to the chain. A recent introduction by APV Baker is a belt stripping unit. A specially profiled belt with notches which passes under the biscuit magazine both supports the column of biscuits and takes one biscuit at a time. The feeders may or may not invert the biscuit before it is deposited in front of pins on the chain of the sandwiching machine.
This unit is a development of an earlier invention offered by the Tenchi Sangyo company of Japan where a notched drum rather than a belt was used to strip and deliver the biscuits. These Peters type machines can also deposit jam (provided the consistency is suitable) and some, including an APV Baker machine, can deposit two creams, or a cream and a jam, as a coextrusion. The interest in the coextrusion of jam is that there is some protection to delay the migration of moisture from the jam into the biscuit and soften it.
Maintenance of the Peters type machines is critical as it is easy for the cream, an abrasive material because of the sugar, to get onto the conveyor chains and cause wear. As the chains wear they elongate and the precision for positioning the biscuits is lost. Haas Hecrona now offers a machine where the chains do not pass near the cream depositors so are relatively well protected from soiling by cream.
The Cookie Capper family of machines work on full-width conveyors as has been mentioned above and Baker Perkins (now APV Baker) have developed a full-width creaming machine of the Peters type with as many tracks as there are lanes of biscuits on the oven band. Only every other biscuit is creamed, the alternate biscuits being used to provide the top biscuit of the sandwich. This machine can run at baking plant speeds (producing up to 100 rows of creamed biscuits per minute), obviates the handling needed to fill feeder magazines and presents the biscuits for cooling and subsequent enrobing in an ideal arrangement. It is, however, very inflexible being limited to a given number of lanes of biscuits (this also defines the size rather precisely) and is therefore best for dedicated production plants where only one type of product is made.
The extrusion, with wire cutting, creaming machines as just described, not only handles firmer creams, but also allows some weight adjustment at the point of cream application. A disadvantage is that at the very high speeds involved with the two- or four lane machines there is frequently damage to the biscuits as they are taken from the feeding magazines. Very fragile or irregularly shaped biscuits, also oval shapes, are difficult or impossible to handle. The lane multiplication and stacking of sandwiches with soft cream may result in distortions that may give difficulties for packaging after the cream is set.
Mixing and handling of creams
Cream may be mixed on batch or continuous systems. The difficulties of handling soft, sticky, messy masses of cream have encouraged more interest in continuous mixing systems for biscuit cream than for dough, although many of the problems are similar. The batch systems usually commence with block or pumped quantities of plasticised fat. Bulk handling of plasticised fats with steep melting curves needs to be critically controlled as small changes in temperature give significant changes in consistency. When the sugar and other ingredients are added, the temperature of the whole is lower than that required in the mixed cream. By a beating and blending action the mass is slowly warmed and there is an incorporation of air. At the end of mixing the cream should have a desired temperature, density and consistency. It is difficult precisely to control all these three features in relation to one another (though consistency is ill-defined) unless close attention is given to the temperatures and qualities of the ingredients. The ranges in properties which are acceptable depend on the type of creaming machine and the type of fat being used. It is advisable regularly to monitor the cream properties and to relate variations with creaming machine performance and biscuit weight control.
Cream densities vary from 0.75 to 1.15 g/cc. In general, the low-density creams are used on depositor type machines and the highest densities on extrusion wire cut machines. However, a cream that has to be pumped any distance to the creaming machine will be subject to considerable pressures and when this pressure is released it is difficult to maintain a homogeneous aerated cream. The lower the cream density the greater will be the volume for a given weight per sandwich. The amount of cream will therefore appear more to the consumer. Many creams are difficult to discharge from a batch mixer, will not flow into pumping systems and have to be man-handled. There are, therefore, labour and hygiene problems.
Continuous mixing systems usually commence with warm fully melted fat and the mixer also aerates and pumps the cream to the appropriate creaming machine. This means there is a need for fat cooling (compared with warming in batch mixing) which requires a scraped surface heat exchanger as part of the system. Metering of icing sugar on a continuous basis is very difficult as big changes in density occur due to static electricity charges in the fine dry powder. This precludes volumetric metering unless much attention is given to powder preparation. The normal procedure is to form a premix of sugar and liquid oil and to pump meter this suspension to the continuous mixer. Other difficult-tometer ingredients such as milk powder and rework can be included with the premix.
The continuous mixer is very similar to a fat chiller and plasticiser and arrangements must be made to accommodate the phenomenon of fat super-cooling. The system pressures required to convey the fat to the creaming machines and back round a ring main can give uniform aeration and density problems. This is because the air bubbles, which are very small under pressure, enlarge and coalesce as the cream is released onto the creaming machine hopper with its agitator. Thus most of these cream systems deliver only high-density creams to the sandwiching machine. Pumping a mixture of fat and sugar presents particular wear and oil-seal problems due to the abrasive nature of sugar.
It is normal to protect these bearings and seals by applying edible oil under pressure into the seals to prevent the leakage of the cream mixture. It is usually best to keep the continuous mixer working at an even speed and to supply the prepared cream in a ring main with take-off points at each creaming machine. The ring main must return to a feed tank that contains all the cream ingredients. Here it must be completely melted prior to reprocessing. If this is not done the quality of cream will vary in its fat crystal and aeration structure.
Cleaning of such a cream system requires some thought. Cleaning will not be necessary if the same flavoured and coloured cream is always used; it will suffice to increase the pipe jacket temperature at the end of a production run and to drain out into a holding vessel. However, if significant changes are required, the system should be washed through with very hot water and allowed to dry. Alternatively, one cream can be followed by another by introducing a ‘mole’ to clear completely the pipework ahead of it.
Creamed biscuit cooling
In most cases, creamed sandwiches are held in a cooling tunnel to set the cream before the biscuits are packed or further processed. Sometimes no cooling is done and the sandwiches are immediately and mechanically fed to wrapping machines. The later arrangement saves space and time, but there is much risk of product spoilage due to the squeezing out of the cream. Only firm low-fat type creams, or biscuits containing very little cream, are suitable for handling without cooling. In some cases, the creamed sandwiches are not cooled and are manually fed into wrapping machines with folded end seals secured by pressure. In these cases not only is there a great likelihood of distortion of the sandwich by manual handling but the biscuits are not rigid enough to permit satisfactory end sealing pressure. The packs are therefore imperfectly sealed with inevitable short shelf life potential.
Sandwiching machinery suppliers have recognised the problems of handling noncooled sandwiches and there are some machines which incorporate biscuit collation and mechanical handling directly into wrapping machines. Where cooling is done, this should be minimal to effect a desired firmness of the cream on the hottest day. Cooling air temperatures should be adjusted so that the biscuits are not taken to below the dew point otherwise condensation will spoil the biscuit shell quality. It is best that the biscuit shells should be as cool as possible before creaming, as cooling of creamed sandwiches is a slow process.
Splitting of creamed sandwiches
Creamed sandwiches should not fall apart (known as splitting) during storage. If they do, the reason may not be obvious. Satisfactory keying of the cream to the shell is achieved by a combination of a sufficiently rough surface into which the cream can be pressed to form a mechanical keying and a migration of melted fat from the cream into the surface of the biscuit prior to it crystallising on cooling. If these situations do not occur to a sufficiently great extent the adhesion may be weak. Thus either the cream should be warmer at depositing, or the biscuit shell should be warmer than the cream (however, see above in relation to biscuit cooling). Good pressure following the topping of the sandwich helps as this presents a great area of contact between cream and biscuit.
Biscuits are hygroscopic and when they take up moisture, they expand. If this expansion should be marked and the cream is hard (as compared with plastic) separation may occur at the biscuit cream interface. A well-aerated cream is more plastic and hence more tolerant to this situation, but it is best not to allow biscuits to pick up moisture. The most elusive form of splitting is that due to fat incompatibility.
Eutectics which affect the melting curves of blends of fats. Should the eutectic which occurs at the cream/biscuit interface, combined with the physical nature of the biscuit surface, be so pronounced as to prevent satisfactory crystal growth in the fat or allow migration of fat away from that area, the bond will be weak and splitting may result. The problem is reduced if the fats used in the biscuit and cream are as compatible as possible. Having made this point, because it was a major problem once encountered and solved by the author with creamed puff biscuits, it must be understood that it is usual for dough fat and cream fat to be dissimilar and, therefore, noncompatible and yet splitting does not normally occur.
Discussion
Fat for cream filling in sandwiching secondary process
Maximum % of lecithin amount in sandwich cream filling
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