Application of Jam, Marshmallow and Caramel Toffee

Additions of jam, marshmallow and caramel appear as very attractive to biscuit developers. Potentially they offer interesting colours, flavours and textures. Jams and fruit pulps, made from high levels of fruit, suggest a "healthy" product! All of these confections are sugar solution based products which present softening problems when in contact with biscuits. Careful compromises in quality must be made to ensure that the biscuits do not soften too much and that the sugar in the confection does not crystallise (becoming fudge-like). The toughness of the confection should be controlled and be related to the biscuit of which it is a part.

Water activity, Aw

The movement of water in these production is governed by a phenomenon known as water activity, often referred to be the sign Aw so it is necessary to discuss briefly the concept.

Knowledge of a product's moisture content does not tell one whether that product if left exposed in an atmosphere of given humidity will loose or gain water. The relationship between a product and its environment is defined by a property known as the water activity. The relative humidity of an atmosphere in equilibrium with a product defines its water activity. Thus a biscuit of 2% moisture may be in equilibrium with an atmosphere of 20%RH. The Aw of the biscuit is said to be 0.2. Thus the relative humidity, RH, scale is from 0 to 100% and the Aw scale is 0 to 1.0.

Knowledge of the Aw of foods is important for several reasons. For example microbiological activity can occur only above Aw 0.65, two materials in contact or in the same enclosure with different Aw values will exchange moisture until they become the same. In the latter case at equilibrium their moisture contents may not be the same but their Aw values will be. Aw values and moisture contents are not the same for all materials because moisture is bound in different ways and the Aw of solutions is related to the gram molecular concentrations of the solutions. (Every molecule has a weight determined by the number of each type of atom that makes up the molecule. The gram molecule is the atomic weight of the molecule in grams.) The smaller the molecules the lower will be the Aw for a given weight-for-weight concentration.

The concept of Aw is very important in biscuit products that have jam or some other sugar syrup as a major part of their composition. Figures 6 and 7 show generalised isotherm of biscuits and sugar solutions. An isotherm shows the relationship between moisture content and water activity at a given temperature.

3c-Biscuit-isotherms-thumbMoisture isotherms of starch and two types of biscuits

3c-syrup-isotherms-thumbMoisture isotherms of sucrose and invert syrups

A biscuit which has been baked "dry" and is then exposed to, or in contact with, a material of higher Aw will gain moisture and become softer. It is quite common for the biscuit thereby to develop a strange flavour and the other material to reach a stage where sugar crystallisation occurs. Thus the dichotomy of texture that was desired is at least partially lost and the eating quality significantly changed.

It should be remembered that it may take a long time for materials with different Aw values to equilibrate. It has been reported, for example, that crackers starting at 3% moisture when held in an atmosphere of 75%RH at 25°C came to equilibrium at 12% moisture after 10 days.

Jam and jelly

There is a range of biscuit products which include jam either deposited as a result of secondary process or added to the dough piece before baking.

Included in products formed as a result of secondary processing are the types where shells are sandwiched together with a layer of jam or jam is deposited in the centre of a ring of cream before or after cream sandwiching, or jam is deposited on a base of sponge prior to half coating with chocolate (for example, Jaffa Cakes), or jam is injected into a soft baked dough before cooling (for example, Jam Lebkuchen). In all these cases it is a requirement that the jam sets rapidly as it cools and before the biscuits are handled for packing or chocolate coating.

Products where "jam" is introduced before baking include fruit filled extrusions (for example, Fig Bars), sponge boats (where jam is deposited on the centre of a batter deposit), various jam toppings where wire cut or deposited dough pieces are garnished with a small deposit of jam, jam pouches where dough is folded over a jam deposit (for example, Pop Tarts which are designed for toasting before eating).

Jam can be considered as a three dimensional network of pectin with syrup held in it. The firmness of the jam is related to the amount of pectin present and the concentration of the sugar syrup which affects its viscosity. The pectin crystals form and interlock as the jam or jelly cools at appropriate pH. If the cooled jam is agitated the pectin network is broken and the jam will not reset. The jam is said to be "broken". If, however, the jam is now heated to about 60°C and allowed to cool the pectin network will partially reform.

Jam is distinguished from jelly principally because it has fibrous or recognisable fruit particles suspended in it and the pectin which causes the setting is derived primarily from the fruit with which it is made. If the insoluble fruit solids are removed a clear jelly is obtained. However, jelly can be made from fruit juice or from commercially prepared pectin and added flavours. In most countries there is a legal requirement to use a certain minimum amount of fruit material in the product if it is described as jam, but jellies, especially if they are called fruit flavoured jellies or merely jellies, need not be made from any fruit base material.

The fibrous pieces in jam present production problems if the jam is to be deposited through small nozzles in precise quantities so jellies are favoured in biscuit manufacture. A jelly made from commercially standardised pectin, sugar, invert sugar or glucose syrup, flavour and colour can be manufactured to close tolerances with a minimum of skill and laboratory control. Recipes for fruit based jam or jellies have to be adjusted to compensate for variations in fruit quality. This requires a considerable degree of skill and experience on the part of the production staff.

Traditionally, bakery jams and jellies have been purchased from specialist suppliers against specifications, but there has been difficulty in defining the viscosity, spreadability, setting characteristics, etc., required for the particular application. As understanding of principles has improved more biscuit manufacturers have decided to make their own jellies (and jams sometimes) so that handling and control is improved.

Caramel

Caramel is formed as a stiff brown mass when sugar is heated to just below its melting point. The flavour is rather bitter. However, when caramel is referred to in connection with biscuit fillings or confectionery, a toffee or butterscotch type of material is implied. These toffees and butterscotches owe their character mainly to the presence of milk, butter and certain hard fats like palm kernel oil when these have been heated together in the presence of sugar. The partial decomposition of the sugar, which gives the characteristic flavour, is known as caramelisation.

Toffees are essentially supersaturated syrups relying on their high viscosities to prevent sucrose crystallisation. However, seeding of the cooling toffee with particles of sugar will cause crystallisation and a fudge will be formed. The texture of a seeded toffee determines whether it is a fudge (with fine crystals) or a grained toffee (with larger crystals).

Toffees (or caramels) used for spreading on biscuit products must,

1. be plastic at ambient temperatures such that they are neither too short nor too tough nor too hard when bitten,

2. have a consistency at about 45°C such that they can be spread evenly and smoothly but be short enough to allow separation from biscuit to biscuit, and

3. have a water activity of around 0.6 such that moisture migrations will not adversely affect the eating qualities of toffee or biscuit .

Soft toffees have a moisture content of about 10% and low Aw so the moisture migration problems are not so much of a problem as with jams and jellies.

Preparation of these toffees to the desired flavours and homogeneity of the fat is a somewhat specialised procedure if between-batch uniformity is to be maintained. As with jams, most biscuit makers purchase the toffee from confectionery manufacturers, but on the other hand most toffee biscuit products also involve chocolate and this puts them into the confectionery market rather than biscuits.

Caramel wafers are a typical biscuit product involving toffee (with or without a layer of cream also). These are formed by spreading a film of toffee onto wafer sheets followed by topping and "book" building as for creamed wafers. The relative humidities of the wafers and the toffee result in an appreciable loss of crispness of the wafer sheets. However, as the toffee proportion is about 70% of the product, the texture of the wafer is subsidiary to that of the toffee.

Process control requires a uniform composition of the toffee in terms of moisture content and consistency which results from the method of manufacture. Small variations in consistency can be compensated for at the time of spreading by alterations to the handling temperature.

Marshmallow

Marshmallow is a mechanically aerated foam composed of sugars in solution and including a foaming or stabilising agent. The latter may be albumen with agar-agar, but is more usually gelatin or Hyfoama a proprietary product. There is now no connection with the shrubby flowering plant called Marshmallow, but the name derives from the past when powder from the root of marshmallow was prepared in a foam "candy" for pharmaceutical purposes.

The moisture contents of marshmallow foams are in the range 15-18% and the Aw values lie mid-way between jellies and toffees. Thus the effects on biscuit bases can be appreciated accordingly.

The marshmallow for biscuits should be short, not rubbery or tough, in texture, so that it can be deposited discretely via nozzles in a similar manner to jelly. The shortness can be promoted by the addition of icing sugar to the foam which causes some crystallisation of the sugar in the syrup.

Marshmallow biscuits may be garnished with desiccated coconut, etc., or enrobed with chocolate. The coconut should be sprinkled on as soon as possible after the marshmallow has been deposited so that it sticks well to the surface. However, it is usual to "skin" the marshmallow a little before enrobing with chocolate. This can be done by holding the product in a low humidity atmosphere at slightly lower temperature for a few minutes before passing to the enrober. It should be noted that moisture migration from the marshmallow into the base biscuit will cause a contraction in volume that may result in pulling away from the chocolate covering or a cracking of the chocolate. If the moisture content of the biscuit can be deliberately raised before the mallow is applied by a period of conditioning in a humid atmosphere, this problem will at least be reduced.

It is important, as with jams and jellies, to prevent drying out of the foam otherwise the marshmallow will become tough and unpleasant as well as contracting in volume. Good moisture-proof packaging is essential and even then the shelf life will be less than for most other biscuit types.

Unlike jellies and toffee, marshmallow must be prepared immediately before use. This involves dissolving the sugar and the gelatin, blending in invert and glucose syrups, cooling, aerating and pumping to the depositing machinery. The recipe and preparation depend on the type of machinery available. Wherever possible an integrated plant for continuous manufacture should be used. This allows superior control of temperatures, pressures and aeration right up to the point of deposition.

The quality of marshmallow is dependent as much on the preparation method as on the quality of the ingredients. As there are many different sets of equipment used to mix, aerate and deposit marshmallow, should problems be encountered the first action should be to refer to the process audit chart and the preparation instructions and check that all has been done correctly and that final temperatures are correct. It is very difficult to generalise about problems and how they should be tackled.

The most commonly encountered problems with marshmallow relate to its structure and consistency, both are strongly influenced by the bloom strength of the gelatin, the total sugar solids, the degree of aeration and the method by which pressure is let down before depositing.

Changes in the smell of the marshmallow during storage may be due to the growth of osmophilic yeasts. Osmophilic means that the microorganisms can exist in high concentration syrups. Great care must be taken to prevent these yeasts from getting into the syrup either during storage or during the manufacture of the marshmallow. Syrup storage tanks must be protected with sterile filters and all handling equipment must be cleaned with appropriate sterilising solutions.