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Sandwich Biscuits

In many cases, sandwich biscuits which have been baked and cooled are subjected to further treatment in the form of coatings or sandwiching with flavoured materials. These treatments are known as secondary processes. The additions include chocolate, fat-based creams, water icing, marshmallow, caramel toffee and jam or jelly. There may be a single addition such as chocolate or a combination of two or more materials. In the latter case, each addition is usually made separately and a cooling or drying period allowed between each.

Secondary processing allows a much greater variety of flavours,  textures and appearance to be achieved than by baking alone. The additions may result in a sandwich biscuit becoming a confectionery product and the materials used are more akin to the sugar confectionery industry than flour confectionery. It may be that chocolate enhances a biscuit or a biscuit fills out and enhances a chocolate product.

In-line secondary processing is not always the case and in many factories baked and cooled biscuits are collected in tins or trays to be coated or sandwiched, etc., at a later time. This is principally because there are staffing complications with in-line secondary processing unless the whole plant can be used every day. It is more usual that the baking plant is used to make a variety of sandwich biscuits and only some of these are further processed before packaging. Furthermore, as ovens become longer and wider the production of biscuits is very fast compared with the speeds of the secondary processing equipment. An in-line arrangement may involve investment in more equipment requiring bigger cooling and drying tunnels which make the whole plant very long both physically and in process time.

It is necessary to balance the savings in labour which can be obtained with an in-line operation against the cost of plant which is idle for some of the time when other products are being baked. Also, one must consider the inefficiencies that occur if one part of a long plant gives trouble necessitating complete stoppage with staff idle followed by difficulties with renewed start up.  Arrangements are sometimes made to use a secondary process plant fed from different ovens by means of alternative conveyor systems. This may allow an optimisation of plant and balance to overall labour requirements. It is unusual to have the secondary process plant mobile to be located on alternative plants.

It will be appreciated that additions to a basic biscuit will always reduce the final precision of size or weight of the product. Thus, packs of creamed sandwich biscuits will always show greater weight variation, on a count basis, at the wrapping machine than if the baked product had been packed without further processing. Secondary processes require special process control attention not only because of the inherent variations that are experienced but also because the materials added, such as chocolate or fat cream, are usually more expensive weight for weight than the base biscuits.

The physical length of production plants with-in-line secondary processing, increases factory communication problems associated with process and production control. Decision-making with respect to start up, shut down and adjustment of successive machines can be greatly aided with electronic equipment such as television cameras, data logging with visual display screens and, of course, automatic control loops. It is difficult to generalise on these devices and aids because there are so many combinations of variables but techniques of control should be considered in great depth at the design stage of long multi-process plants.

Most manufacturers separate secondary processes in their factory at least until demand makes it economic to invest in specially integrated plant. Handling and storage of product between stages necessitates consideration of techniques and facilities that will protect against breakage and spoilage due to temperature or moisture pick-up. Baked products at low moisture contents are very hygroscopic so it is most important to preserve freshness by storing them in well-sealed containers or in specially conditioned rooms. Reusable containers are prone to damage resulting in lids not fitting well. Moisture pick-up from the atmosphere is surprisingly rapid as Fig 1 shows below. It will be seen that exposure for even one hour may result in a biscuit which has significantly less crisp eating characteristics.

Sandwich biscuits which are transported around in tins can become marked where they are in contact with the metal (paper linings will prevent this) and crumbs, creams, chocolate, etc., will soil the container making it necessary to do some cleaning to prevent contamination with later products. It is very common to see casual attitudes in respect of protection of trayed-up stock. Maintenance of the containers can be a problem if insufficient attention is given to the size and design for optimum use and handling.

Sandwich creams: Types of creamed products

Creamed sandwich biscuits occupy a significant place in the world biscuit market. Typically, two identical biscuits (the shells) contain a layer of sweet or savoury fat cream. There are many variations on this basic type. For example, the shells may be dissimilar in shape or colour and one shell may have a hole (or holes) through which the cream can be seen or in which jam is deposited. Creamed sandwich biscuits may be enrobed with chocolate to form a count line (a product that is wrapped and sold individually) or they may form the centre of a moulded chocolate bar. The sandwich may be formed with wafer sheets in which case it may have multiple, two or more, layers of cream between wafer sheets. The same type of cream may be deposited on a biscuit base but with no topping biscuit followed by chocolate enrobing.

Fig 1: Typical rate of moisture pick-up of biscuits in an atmosphere of about 70% RH

 

The cream offers extensive opportunities for variations in flavours, colours and improved acceptability of a biscuit. The weight of cream is typically around 30% of the creamed sandwich, but amounts within the range 20–36% can be found. In general, the larger the biscuit the lower the percentage of cream. Wafer sandwich biscuits with two layers of cream usually are much richer, about 70% of cream by weight. As will be explained later, the quantity of cream is related to the density of it and the hardness of the biscuit shells used to make the sandwich.

Composition of the cream

In sweet creams the major ingredients are sugar and fat. The nature and quantity of fat is paramount for determining the characteristics of the cream. Whether the emphasis is given to having low or high percentages of fat in the cream depends on the relative costs of fat and sugar and also on the nutritional information that maybe displayed on the wrapper. It is usual to use a recipe which has around 30% fat in the cream, but levels as low as 23% and as high as 45% are found. The sugar, sucrose, should be in a powdered form with few, if any, large crystals. When eaten, the sugar should not be gritty in the mouth and the smaller the particle size the more readily will it dissolve. However, there must be a balance as the finer the particle size, the more fat is required to give the desired consistency for cream sandwiching.

Flavouring materials such as skimmed milk powder, fruit acids (citric, tartaric and malic), cocoa powder and natural or synthetic flavours may be added to the base cream. Natural or permitted artificial colours also add very significantly to the attraction and often ‘point’ a flavour. By this is meant that if the cream is coloured appropriate to the flavour involved, there is more conviction about the taste than if the basic flavour level is increased. White uncoloured creams require the consumer to think more about the flavour present.

There is often a concern that the cream is very sweet. Dextrose monohydrate may be used as a partial substitute for sucrose. It has the attractive quality of giving a cooling sensation when dissolved in the mouth and it is also less sweet than sucrose. It may be less expensive than sucrose. Starches such as corn, potato and rice have been used as fillers and cream ‘driers’, but they do not generally improve the cream flavour, texture or sweetness. In the USA the style is for softer creams which use softer fats and some starch.

The cream is more pliable, very stable in consistency as the temperature changes, not so attractive to eat and, during processing, very difficult to pump. There are certain similarities in the consistency of biscuit creams and chocolate since they are both fat/sugar mixtures. The important features are the effects of moisture and emulsifiers. Small additions of water cause a considerable increase in consistency which may or may not be desirable. The use of lecithin as an emulsifier, at a level of around 0.2% of the fat weight, reduces the consistency. Lecithin aids the mixing of the cream and the effect of moisture is mentioned because it is often convenient or desirable to add colours as aqueous solutions. Powder colours (lakes) are much more expensive and, in the average cream mixer, more difficult to disperse uniformly.

The fat demands some detailed consideration becasue it affects not only the eating characteristics of the creamed biscuit, but also other important aspects of process and quality. The requirement is that the cream in the sandwich should be firm at ambient temperature. This is from the point of view of maintaining the sandwich biscuit in the shape that is desired, and so that as the biscuit is broken or bitten the cream does not squeeze out. The harder the biscuit, the harder should be the cream. As the biscuit is hewed the fat in the cream should melt rapidly to release the sugar and other ingredients giving maximum flavour sensation. There should be a minimum of unmelted fat at blood temperature otherwise an unpleasant greasy film will remain on the roof of the mouth. Between about 20ºC (ambient) and 37ºC (blood heat), there should be a large change in fat solids. The types of fat that exhibit these characteristics are discussed fully in Chapter 11 but the best types are coconut and palm kernel oils, and their hardened derivatives, which have very steep melting curves.

The rapid melting characteristics present difficulties in cream handling and processing. They result in large changes of consistency with little temperature change so that the mixing and ambient temperatures in the factory can be important. Some manufacturers ease the problem by using winter and summer blends of fat in their creams, but there is often confusion about whether this is to suit the customer who eats the biscuit or the creaming machine! Blood heat remains the same throughout the year and with centrally heated homes ambient conditions for the consumer in temperate climates do not alter very greatly. There are also the problems of knowing when hot summer weather can be expected and how long the packets of biscuits will be in the shops before purchase.

Another factor which affects the firmness of a fat-based product is the degree of plasticity of the fat. If the fat has been allowed to solidify passively from a fairly fluid condition, it will be much harder at any given temperature than if it has been cooled under agitation. Since the handling of cream for sandwiching involves much agitation, it follows that the smaller the temperature differential between the cream at the time of handling to the ambient when the biscuit is eaten the less firm will be the cream at a given fat content. The higher the fat content, the firmer will be the cream under these conditions. It is necessary to have a certain minimum change in fat solids between the time of creaming sandwiching and when the biscuit is eaten otherwise there will not be enough keying of the cream to the biscuit surface resulting in the shells falling away from the cream. Therefore, as with so many processes involved in sandwich biscuit manufacture, it is best to make as much provision as possible to keep cream ingredients and machine temperatures constant from one season to the next.

In countries with high ambient conditions, the choice of fats for cream is more restricted as a suitable hardened palm kernel oil will have a significant waxy tail which will be unpleasant when eaten. It is therefore common for biscuit manufacturers in hot countries to use the same fat for biscuit creams as is used for doughs. Most cream sandwich biscuits have a thickness of cream that is readily seen between the shells. Economic trends have resulted in some sandwiches having less cream, to an extent that the filling appears more like a layer of adhesive than a true sandwich. In these creams, it is possible to use a fat that has a much slower melting curve with inherent advantages in machinability of the cream. It is felt that moves in this direction while simplifying the technology of control are to the detriment of biscuit quality.

Cream formulations sometimes include rework material. That is, broken or misshapened sandwich biscuits which have been ground up. This tends to ‘dry’ the cream and give it a browner or greyer colour. The practice is not recommended, but it is economically expedient in some cases, particularly for wafer creams where the cutting of the creamed books always results in a lot of cream-rich ‘waste’. An exception to this situation is in the preparation of savoury creams. Here the use of sucrose as the filler is precluded and palatable non-sweet alternatives are not many. Ground (savoury) biscuits offer a possible filler along with lactose, whey powder and maltodextrins, all of which have low sweetness values and blend well with cheese powders, etc.

Creamed biscuits are common components of packs of assorted biscuits. In these packs, there may be a problem of flavour migration during storage. Flavour ingredients whether natural or synthetic, are very volatile. It is possible to obtain flavours which have been flavour ‘locked’ in some way, such as microencapsulation, so that their smell is greatly reduced but when eaten the flavour is released in the mouth by mastication or dissolution in water. These special flavours are, of course, more expensive, but their use in biscuit creams is worth considering should it be necessary to improve the quality of sandwich biscuits in assorted packs.

 

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