Biscuit Handling

Requirements for biscuit handling

After baking, most biscuit go straight to be packaged. This is not only to collate them into practical sized groups for sale, but also to protect them from moisture uptake from the atmosphere, dirt and damage. The transportation from the exit of the oven to the point of packaging may be of significant distance so long and multiple conveyors may be involved. Often different types of biscuits produced from an oven are packed with different packaging machines. By introducing curved and diversion conveyors the biscuits can be taken to the appropriate place. It is inevitable that during transportation the biscuits cool.

Also, before arriving at the packaging point, it has been traditional to stack the biscuits so that it is easier to pick up several at a time to transfer them to packaging machines. In many cases the number of lanes of biscuits on the oven band is too great for convenient transfer of product, after it has been stacked, into packaging or secondary processing machines. Arrangements in the conveying system for lane reduction or more precise alignment are then included.

In many cases baked biscuits designed for secondary processing are taken directly to the next stage from the oven. However either because the location of the secondary processing machines does not allow direct transfer, or because the capacity of these machines cannot cope with the speed that the biscuits are baked, it is necessary to collect the biscuits in boxes for later use.

Collection in boxes may also be necessary if packs of assorted biscuit types are to be made when biscuits from different baking plants are involved.

Transportation

Typically biscuits are taken from the oven band onto a conveyor of the same width. The conveyors are usually of fabric construction, full width and arranged in one or two tiers. They allow the biscuits to cool flat in the ambient air or, in certain cases, under controlled environment conditions. They are usually designed to run slightly faster than the oven band to allow good separation of the rows of biscuits. By using radial bends and various turnover devices they can be used to take the biscuits wherever needed within the factory.

In some factories, especially where space is more restricted, biscuits are stacked immediately after leaving the oven band. In these cases, to aid cooling, the conveyor may be a wire mesh and cooling air is blown through this from below.

Very small biscuits, such as snack crackers, may be diverted immediately from the oven band onto a narrow transverse conveyor for transportation to a bulk holding container prior to packaging. Handling in this way exposes the biscuits to damage as they are dropped and jumbled together.

Cooling

It is common for equipment suppliers to recommend extensive cooling conveyors. When biscuits are manually transferred to wrapping machines etc. after cooling it is clearly necessary to have the products cool enough for handling. Cooling is also necessary for sugar rich biscuits as these are very soft and plastic as they leave the oven and only set rigid when cool.

With the introduction of mechanised handling it is not necessary to worry about what is acceptable to human hands but many feel that if the biscuits are packed too hot they will sweat in the pack. In other words there is thought to be a significant loss of moisture while the biscuits are cooling.

It is probable that cooling arrangements are mostly excessive. The "rule of thumb" cooling times on open conveyors given by machinery suppliers range from 50 to 200% of the baking time. In some cases biscuits are stacked immediately after removal from the oven band and then cooled on wire conveyors with fans blowing air from below or in forced convection tunnels with or without refrigeration.

Long cooling conveyors usually involve transfers and often turnovers between the oven exit and the final destination. With increased mechanisation of biscuits it is most important that the uniform orientation of the biscuits on the oven band is maintained to the handling machines before wrapping etc. A jumbled positioning means that the handling mechanisms are less efficient. The longer the cooling conveyors and the more the transfer points, the more disorientated the biscuit positioning becomes. Therefore, there is a need for minimal cooling and transportation before packaging.

Cooling requirements before and after secondary processing are dealt with elsewhere.

Certain groups of biscuits are prone to spontaneous breakage at variable times (up to 24 hours) after cooling and packaging. This is known as "checking". It is caused principally as a result of moisture equilibration during cooling. The wetter parts contract as they lose moisture and the drier parts expand. This creates tensions that result in cracks. Checking can be reduced or eliminated if the baking is such that there is a low moisture gradient between the centre and each edge as the biscuit leaves the oven. The use of a post oven dielectric drier (make link) by applying heat preferentially in the wettest parts of the biscuit can effectively eliminate checking irrespective of the subsequent cooling arrangements and for this reason, as well as others, dielectric (radio frequency) units are extremely useful.

4caTwoTierCooler-thumbTypical two tier biscuit cooler

The cooling conveyors are usually designed to run slightly faster than the oven band to allow good separation of the rows of biscuits. It is helpful to have at least one transfer point in the conveyor system to turn the biscuits over so that cooling of the biscuit bases can occur.

Subsequent biscuit handling is improved if the ordered regimentation of the biscuits, which is present on the oven band, is maintained as nearly as possible throughout cooling. Thus, transfers at the oven stripper and at other places during cooling, should be designed to keep the lanes and rows straight.

Lane adjustments

It may be expedient to change the number of lanes of biscuits resulting from the cutter to suit the wrapping machine feeders, the number of operators employed, or to mix the biscuits from different rows in the interest of more uniform pack weights. Many devices have been designed to lane reduce, lane distribute and lane multiply. Mostly they are simple deflector devices which aim to push the biscuits sideways without arresting their forward movement. It has been possible to introduce some electronic sensing and servo operations to compensate for lane wander as a result of band tracking, etc. By using relatively inexpensive micro-electronic devices, much more sophistication can now be used. This includes

  • programming of wrapping machines,
  • feeders to collect biscuits from across the lanes to balance weights and variable supply in different lanes,
  • adjustment of lane reducers to suit groups of wrapping machines working in parallel but with any individual machines being stopped on a random basis,
  • arranging logical plant shut down,
  • deflection of product should hold ups occur in the wrapping area.

Alarms can be arranged to call staff for manual assistance should the automatic arrangements reach a saturation point. By these means the amount of labour needed in the wrapping area can be considerably reduced making big improvements to the plant efficiencies.

Biscuit stacking

At the end of the cooling conveyors is a stacking machine. The function of this machine is to collect biscuits from the cooling conveyor, form them into lanes and stack them on edge or overlapping each other for easier handling. The performance of the stacking machine may be improved if the spacing between rows is increased before the biscuits reach it. To effect this a stacker feed conveyor with separate drive may be used.

Stacking may be effected by different techniques, but the main types are, star wheel stacking, penny stacking and flip stacking.

4caStarWheelStacker-thumbPrinciple of the star wheel stacker

4caPennyStacker-thumbPrinciple of the penny stacker

4caFlipStacker-thumbPrinciple of the flip stacker and vertical stacking

The mechanism of the first two should be clear from the diagrams. The flip stacker relies on an acceleration by a fast rotating flipping roller which throws each biscuit forward over the one before it. It may be necessary, as shown in the diagram, to have a trailing chain or web to control the flight of the biscuits. The flip stacker can stack at very high speeds and is superior in this respect to the other types. The star wheel stacker allows a more vertical orientation of the biscuits, but this orientation is possible from the other types if there is a transfer to a slower moving vertical stacking band or if the stacking is done onto vibrated inclined conveyors.

Vibratory conveyors have become a popular and useful means of stacking and feeding biscuits to the in-feeds of wrapping machines. These U-shaped single lane conveyors are gently sloping and biscuits fed onto them are both transported and, as they bunch up, they are stacked. The added advantage is that they can form a buffer storage because the bunched biscuits occupy much less room than those being transported flat.

The stacking machine usually stacks the biscuits directly onto the packing table (or the table beside a cream sandwiching machine). The height of this conveyor is to suit operators sitting or standing by it while they transfer the biscuits to wrapping machines, individual packets or into tins or trays. Guide strips of steel are usually fitted at appropriate spacing across the packing table to collect the lanes from the stacker and to maintain them along the packing table.

If the feeding of the wrapping machines, creaming machines, etc. is automatic, the packing table also provides a reservoir should there be breaks in the running of either the production plant or the wrapping machines. It will be appreciated that recycled biscuits can also be introduced to the system on this packing table. The recycled biscuits may result from opened defective or lightweight packs, or from trayed up product collected at some previous time when a wrapping machine was stopped, etc.

Biscuits which for one reason or another are not packaged or trayed up will fall off the end of the packing table and should be collected in suitable containers. In an efficient operation, only unpackable product should be allowed to reach the end of the packing table.

Only the main features of biscuit handling techniques and possibilities have been outlined. Very many ingenious and special systems have been designed, including the use of air jets, air beds and vibrator arrangements, to move the biscuits to predetermined positions. Although the cheapest way in most cases, gravity is not a very reliable method. Falling biscuits can easily be deflected or retarded by air currents, and friction alters with the humidity of the day or the cleanliness of the conveyor. When biscuits are passing at very high speeds and very close together the movement of each one must be identical if uniform performance with no jam-ups is to be achieved.

Boxing up

There will be occasions where biscuits are not packed, or submitted for secondary processing, directly. These must be collected for later use.

Normally such biscuits are manually transferred into large plastic or metal boxes from the packing table. The process is labour intensive and less efficient than immediate use for packaging. There will always be some breakage involved.

Care must be taken that the boxed biscuits are kept clean and protected from moisture in the atmosphere. The boxes must be regularly washed and dried before use and as they will be stacked they should never be placed on the floor, always on pallets or other clean stillage. Each box should have a well fitting lid. Bent, split or damaged boxes must be discarded as protection of biscuits against moisture is fundamental to good eating quality.

Recycled biscuits

Biscuits retrieved from damaged packs or from light-weight packs that have been rejected together with biscuits that were boxed up because of a stoppage of the wrapping machine are commonly fed back with new product on the packing table.

Care must be taken that product with significantly different baked colour is not mixed as consumers will find inconsistent eating qualities which will be viewed as poor quality.