5 Sugars and syrups 5.1 Types of crystalline sugars 5.1.1 Sucrose, ‘sugar’ Sucrose is a medium sized molecule, known as a dissacharide (composed of a unit of dextrose plus a unit of fructose). It is derived from sugar cane or sugar beet which has been refined and crystallised from a concentrated solution. The term sugar is commonly used to refer to sucrose. It is by far the most commonly used type of sugar in the biscuit industry. White sucrose is available in various particle sizes, for example granulated, castor and icing. The smaller the crystal size the more quickly the sugar dissolves either in a dough mix or in the mouth. Brown sugars are either partially refined sucrose, so still have syrup over their crystals, or are manufactured from white sugar by adding syrup to it. Commonly used brown sugars are demarara (with large crystal size), muscavado and soft pieces (various names are used and these sugars usually have small crystal size). London demarara is an example of a manufactured brown sugar where syrup has been added to white crystals. All brown sugars are sticky and tend to form hard lumps on storage especially after the bag is opened and exposed to the air. 5.1.2 Lower sugars Lower sugars have smaller molecules than sucrose. They are mostly known as monosaccharides (e.g. one unit of dextrose or fructose) with reducing properties in chemical reactions (described later in relation to the Maillard reaction in Section 5.4.6). They are normally derived from sucrose or from a starch (which has very large molecules made up of multiple units of dextrose) by a process which splits the molecules into individual units. This process is called hydrolysis. The most commonly used lower sugar is dextrose (dextrose 29 30 Biscuit, cookie and cracker manufacturing manuals monohydrate). Another lower sugar is fructose which is similar to dextrose but is much sweeter. (Fructose is a sugar that can be eaten safely by persons suffering from diabetes.) Maltodextrin is a mixture of partially hydrolysed molecules of starch. It has a low sweetness but is readily soluble. These lower sugars are often used in the biscuit industry in the form of syrups (see Section 5.3.2). 5.2 Relative sweetness Relative sweetness of sugars used in baking: Fructose Sucrose Dextrose 62DE Glucose syrup Maltose 42DE Glucose syrup Lactose DE is the dextrose equivalent. 173 100 74 60 32 30 16 5.3 Types of Syrup 5.3.1 Syrups based on sucrose Liquid sugar (this is a somewhat confusing term given to a solution of sucrose) has 67% solids and 33% water. Invert syrup is derived by hydrolysing sucrose into its components, dextrose and fructose. This is easily done with acid. The acid is neutralised after the reaction is complete. Amber to dark syrups vary from pale coloured syrups like golden syrup (which has about 38% invert sugars, with the rest as sucrose) through darker types to treacle and ultimately molasses. As the colour darkens the flavour increases and becomes progressively more bitter. All sucrose-based syrups usually have 80% solids and 20% water. 5.3.2 Syrups derived from starch All syrups derived from starch usually have 70% solids and 30% water. Sugars and syrups 31 Glucose syrups, 42DE, 63DE, 90DE, etc. at ambient tempera- tures are very thick due to the presence of large molecules such as dextrins which are partially hydrolysed starch. Glucose syrups are generally not as sweet as sucrose syrups. The term DE is used to indicate the apparent concentration of dextrose, or other reducing sugars, and hence the sweetness and reducing power. Thus DE42 indicates that the syrup has a similar performance to a 42% solution of dextrose. High fructose corn syrup (HFCS) is a type of glucose syrup. The hydrolysis of starch has been achieved with special enzymes that favour the production of fructose rather than dextrose. The concentration of fructose in relation to other sugars is in the range 4&90%. This means that the syrup is much sweeter in taste than a normal glucose syrup. 5.3.3 Other syrups Malt extract is rich in the sugar maltose which although a disaccharide is a reducing sugar. Malt extract is used principally for its flavour. It is usually made from germinating barley by extracting water and concentrating the syrup to 80% solids. Malt is rich in the enzyme amylase which breaks down starch and sugar. When using malt extracts in biscuit doughs only non-diastatic syrup should be used in which the enzymes have been deactivated by heat. Honey is similar in composition to invert syrup. It is therefore a mixture of reducing sugars. Honey is expensive and is used principally for its flavour. Lactose (may be crystalline) is a sugar derived from milk, a disaccharide (unit of dextrose plus unit of gallatose) 5.4 Uses and functions of sugars and syrups 5.4.1 Uses in biscuit doughs Sugars are important in the taste and structure of most biscuits. Relatively large quantities of sucrose and syrups are used in all short doughs, smaller quantities in semi-sweet doughs and to a much lesser extent in cracker doughs and wafer batters. In short doughs there is not normally enough water in the formulation to allow all the sugar to dissolve so the crystal size of the sucrose used affects the eating characteristics of the baked biscuit. 32 Biscuit, cookie and cracker manufacturing manuals 5.4.2 Uses in biscuit filling creams In biscuit filling creams there is a need to have a smooth mouthfeel and rapid dissolution of the sugar in the mouth. Fine particle sized sucrose, icing sugar, is used. Sometimes some dextrose is used to reduce the overall sweetness. Dextrose (usually used as the monohydrate) has a negative heat of solution giving an attractive cool mouthfeel as it dissolves. 5.4.3 Mixtures of sucrose and invert sugars are important in jams and jellies. The concentration of the sugars must be at least as high as 67% to prevent microbial spoilage and in jams used for biscuits the concentration may be as high as 78%. Uses in jams and jellies 5.4.4 Use in marshmallow Marshmallow is a foamed mixture of sugar syrups and a gelling agent such as gelatin or agar agar. 5.4.5 Uses in chocolate Sugar is a major ingredient in chocolate. In the course of manufacture the chocolate is ground very finely so that it is not possible to detect the sugar crystals when the chocolate is eaten. 5.4.6 Function or sugars in biscuits For sweetness and flavour. The brown sugars and sucrose syrups are valuable sources of flavour in biscuits. For structure and hardness, particularly in short doughs. High levels of sucrose give hard glassy textures. This is because molten, concentrated sugar solutions, which are formed when the dough pieces are heated in the oven, set on cooling. If some glucose syrup is added to the formulation the hardness may be reduced at a given level of sucrose. As a bulking agent in creams and chocolate. The sucrose is used not only for its sweetness but as a filler that dissolves readily when eaten. As a flavour enhancer and to make flavours seem correct. Small Sugars and syrupa 33 quantities of sucrose allow a much greater appreciation of certain flavours. Salt is another common flavour enhancer. Some flavours do not seem correct unless they are in a sweet context. Good examples are fruit flavours which are associated with sweetness and often acidity. As a fermentation food. In doughs that are fermented, such as cream crackers, additions of small quantities of sugar encourage the yeast to grow more vigorously and hence speed the fermentation process. To aid surface coloration during baking. Only the reducing sugars do this. During baking the reducing sugars combine with amino acids from proteins (found in flour, milk products and eggs) in a complex reaction known as the Maillard reaction. This reaction gives attractive foxy brown colours on the surface of baked goods. The higher the concentration of the reducing sugars present the darker the colours produced. The Maillard reaction is also more prevalent in alkaline than acid conditions and this is one of the reasons why sodium bicarbonate is used in biscuit recipes to increase the alkalinity. As a decoration on the surface of biscuits. Sucrose crystals dusted on to the surface of dough pieces before baking adhere strongly and add to the attractive appearance of the biscuits. The size of the crystals is critical to obtain the desired effect. In some cases where hot oven conditions are used and the expansion of the dough piece is great during baking it is possible to melt the sucrose on the biscuit surface to obtain a sugar glaze. 5.5 Importance of sucrose particle size The particle size of sucrose affects the following products: Mouth feel. Important in sandwich creams and short dough biscuits. Small crystals feel smooth and dissolve quickly, larger ones give gritty or crunchy textures. Rate of solution. When mixing doughs time must be allowed for as much of the sugar as possible to dissolve in the available water. There may be competition for this water between sugar and starchy materials. Thus if more sugar should be dissolved use a fine particle size. Spread control. Some short dough biscuits increase in diameter, length and width during baking. These changes in size are usually 34 Biscuit, cookie and cracker manufacturing manuals related to the quantity of sugar and its particle size. Sugar with small particle size results in more spread than coarse particles. A variation in sugar particle size when supplied to the mixer for the dough can give process control problems. Appearance when used as surface decoration. Sugar of various sizes from large crystals to icing sugar is used to dust the surface of dough pieces before baking. In most cases the sugar remains unchanged after baking but in certain biscuit types if the sugar particles are small they melt on the dough surface due to the oven heat and produce an attractive glaze. Sucrose is normally purchased as granulated sugar. The crystal size range is quite high but this grade is free flowing and remains so for a long time if correctly stored. Finer particle sized sucrose is often produced by milling in the factory. The product of milling is initially powdered sugar (with a large particle size range) which is often used' in doughs because the smaller particles dissolve more rapidly. By sieving powdered sugar, to remove the large particles, a fine powder, icing sugar may be obtained. If powdered or icing sugar is purchased there is a great probability of it becoming lumpy because of the very large surface area exposed by the small particles. Moisture from the atmosphere coats the powder particles and crystals may form causing caking. Caking can be reduced, but not eliminated, by adding small quantities of an anticaking agent such as tricalcium phosphate or corn starch. Generally it is better to make powder sugar immediately before it is needed. Caster sugar is not as fine as powdered sugar. It is stable in terms of caking but is much more expensive than granulated sugar. 5.6 Delivery and quality testing of sugars and syrups 5.6.1 Crystal sugars Crystal sugars are delivered either in bags or in bulk. Icing sugar is always in bags as it is difficult to handle in bulk and brown sugars are always in bags because they are sticky. Bulk handling of sugar is considered below. Crystal sugars are normally tested on arrival at the factory for particle size distribution. This is done by sieving through a series of sieves and measuring the proportions held on each sieve. The results of this test can be compared with the specification given by the supplier for the grade of sugar being checked. Sugars and syrups 35 5.6.2 Syrups Syrups may be delivered either in barrels of steel or plastic, or in bulk in which case the load is warm to aid transfers. Syrups are normally tested for flavour (against a reference sample), colour and solids concentration. The latter test is done simply, using a refractometer. A small quantity is put onto the sample surface and the refractometer is closed. A measurement is made by viewing through the eyepiece. The solids will be about 80% for sucrose syrups and 70% for invert and glucose syrups. 5.7 Storage and handling of sugars and syrups 5.7.1 Crystal sugars in bulk Sugars delivered by road tanker are transferred to the silo pneumatically in a similar way to flour. As the sugar passes along the pipe there is a great tendency for the crystals to break up. This problem is reduced if the offloading is done at a moderate and not too fast a rate and if the pipe has a minimum number of bends between the tanker and the silo top. In the silo there are potential problems of caking, the formation of lumps when crystals fuse together. This happens when there are temperature changes within the mass of sugar. As heat is applied, for example from a warm wall of the silo, the minute films of sugar solution around each crystal are dried out allowing crystals to form and causing adjacent crystals to fuse together. Caking of sugar is always a moisture migration problem initiated by temperature gradients. Insulation of the silos is the best method of preventing caking. Sometimes the lumps so formed are very hard and very large! They have to be removed by someone entering the silo which is not a pleasant job. Bulk sugar is drawn from the base of the silo through a rotary seal into a pneumatic air line in a similar way to flour (see Fig. 2). The sugar is delivered to a weigh hopper but excess sugar is never returned to the silo as it will have been broken a little in transit and it is undesirable that dusty sugar is returned to the silo. Any excess sugar in the line after the hopper has made weight should be collected in a special bin sited near the mixing department. There is a great hazard of dust explosions from sugar dust. Much care must be taken to avoid sparks from machinery or static electricity in sugar handling systems. 36 Biscuit, cookie and cracker manufacturing manuals It is not usual to empty or clean sugar silos except when it is necessary to clear lumps, sugar caked onto the silo walls or collections of dust. 5.7.2 Crystal sugars in bags The importance of sugar particle size distribution for many short dough biscuit types means that handling sugar in bags is desirable to reduce process variations. Pneumatic handling causes haphazard crystal breakdown. The disadvantage of bags is that the usage of sugar is typically high and the labour involved in handling the bags is considerable. Take particular care to remove string, labels and other pieces of paper when opening and emptying bags. Sugar, whether in bags or bulk, has a long shelf life. If the bags are kept in a dry place at even temperature the sugar will not become lumpy. 5.7.3 syrups In bulk, syrups are held in warm insulated tanks. The temperature is maintained within close limits because this affects the viscosity of the syrup and also the temperature of the dough in which it is used. The syrup is pumped .directly from the road tanker via a filter into the holding tank. There is a potential for fermentation in stored syrups arising from yeast cells present in the air, growing in weak solutions formed at the head of tanks. Microbiological filters should be installed to clean the air which is drawn into the silo as it empties. However fermentation cannot be entirely prevented so the silo tanks must be cleaned periodically. The main area where fermentation occurs is in the headspace of the tank where condensation causes more dilute sugar solutions to be formed. The bottom of the silo is designed to slope away from the exit pipe because there is commonly a small amount of sedimentation from stored syrups. Silos should be cleaned and sterilised regularly with very hot water. Storage times are limited due to the potential for microbial spoilage. These times are about four weeks for liquid sugar, one or two weeks for glucose syrup. Sugars and syrups 37 The syrup is taken from the tank to the mixer via a warmed pipe and a metering pump. Commonly syrups are used from barrels. Cold syrups may be very viscous and difficult to run or pump out. Thus it is normal to store barrels in a warm place or, in cold weather, to have an electrically heated jacket to warm the barrel. All syrups are sterile until opened so have an indefinite shelf life. 5.8 Other sweeteners There is widespread concern that sugars accelerate tooth decay and provide excess calories in the diet. Many foods are made with artificial sweeteners to replace sugar. These sweeteners give intensely sweet mouth perceptions compared with sucrose. In baked goods, replacement of the sugars is not satisfactory because of the structural importance that sugars give to the products. However, very small quantities of saccharin and cyclamate may be used to increase biscuit sweetness in, for example, semi-sweet biscuits where the amount of sugar that can be used in the formulation is limited. Claims that biscuits are ‘sugar free’ should be examined critically as what is often meant is ‘sucrose free’. The sweetness comes from fruit syrups which are essentially free from sucrose but consist of lower sugars which have as many calories per gram and also as much affect on tooth decay! Polyols such as sorbitol, mannitol, xylitol, lactitol and maltitol (which are solid sweet materials with the chemical structure of alcohols and not like the sugars that have been described above) are used in chocolates for persons suffering from diabetes and those wishing to eat more ‘tooth friendly’ products but they are not satisfactory for baked products.