6 Fats, oils and butter 6.1 Fats and oils The only difference between a fat and an edible oil is that at ambient temperature a fat is semi-solid, and appears more or less firm to the touch, and an oil is liquid. They are both of similar general chemical composition. Edible oils are completely different in chemical form to mineral oils that are used as fuels or for lubrication. Most mineral oils are hazardous to human health and should not be even a small component of food. In addition to butter, which is a well known fat used in baking, there is a wide range of vegetable, animal and fish fats used in biscuit manufacturing. In all cases the fat will have been refined and deodorised. This process removes colours, acids and other unplea- sant flavours that occur naturally in fats extracted from various sources and that develop during storage. In many cases the fat refiner can modify the fats by physical and chemical means so that more or less any physical form of fat is theoretically possible. Since these changes can be expensive, the modified fats that are commonly encountered by biscuit manufac- turers are limited to blends with particular characters or fats that have been ‘hardened’ to raise their melting temperatures. 6.2 Butter and butter oil Butter is used both for its shortening and its flavour effects. It is much more expensive than other fats but there is no doubt that its flavour contribution is substantial and desirable in biscuits. Neither butter nor butter oil is refined or chemically modified. Butter is an emulsified mixture of milk fat, water and a small amount of protein. The normal maximum permitted water content is 16%. Butter varies in quality depending on its origin and the season of the year and also on whether it contains whey cream where lactic 38 Fats, oils and butter 39 yeast was used in its manufacture. It may be sold salted or unsalted. If salted about 1.5% of salt is normally added. The flavour of butter is complemented during baking by vanilla and sugar. In the course of biscuit baking the fresh butter flavour changes to a mild toffee or butterscotch note which has both good flavour and aroma. A baked butter flavour is enhanced with minimum baking time at high temperature. The handling of butter has become a major obstacle to its large scale use. Butter from creameries is nearly always packed in plastic lined cartons of about 12.5 kg. It should be kept in cold store at about 4°C to preserve its freshness. The optimum temperature for use in biscuit doughs is about 17- 18°C and it takes many hours for blocks at 4°C to rise to a convenient and uniform temperature. It is not practical to melt the butter and replasticise it in the bakery and it is also not practical to bulk handle the butter by means of pumps and pipe lines whilst still maintaining the typical properties. Thus, it is necessary to raise the butter temperature either by conditioning it in temperature controlled rooms for perhaps 48 h or to increase the temperature more rapidly, for example, with microwave energy. A rapid heating method usually requires that the temperature and plasticity are equilibrated by working and pressing the butter through a mincer-type machine with a die plate giving about 4mm diameter extrusions. Even so, a considerable amount of manual handling is needed and in a warm bakery it is easy for butter to become too soft before use. At high ambient temperature butter will become rancid within a few weeks. Butter fat may also be purchased as butter oil without any appreciable moisture and protein. Blocks of butter oil are not normally plasticised making them much harder than butter. The flavour imparted to biscuits made from butter oil instead of butter is much inferior, so that butter oil is not a popular ingredient for biscuits. It may be possible to purchase butter that has been ‘denatured’ with sugar. If the quantity of sugar added is known this can be a useful ingredient for biscuits. It is usually cheaper than real butter. 6.3 Margarine When first invented margarine was a butter substitute made from oils other than milk fat. There are now many different margarines 40 Biscuit, cookie and cracker manufacturing manuals developed for special purposes. Normally margarines will have a content of about 16% water, as does butter, and they are emulsified and plasticised so that their consistencies resemble butter. The consistency can be modified by using fats with specific melting temperatures, a feature that is not possible with butter. Because they are emulsified and plasticised, margarines are supplied and handled like butter. Temperature control of the storage, especially before use, is of key importance. Not all boxed fat is margarine. In fact it is not usual to use margarine which contains water in biscuit manufacturing. Boxed fats are normally plasticised shortenings and these will be described below. 6.4 Rancidity Fats, more than any of the other ingredients used to make biscuits, can cause quality problems. The main problem is rancidity which is manifest as unpleasant flavours. Oxidative rancidity, which is the most common type, happens when fats are exposed to the air. Certain chemical bonds in the fats change to produce new substances which even when present at very low concentrations render the fats unsuitable for use. These changes are more likely in fats which are liquid at ambient temperatures. There are also some handling conditions that accelerate these oxidative changes. For example, when handling fats warm and in bulk, agitation that promotes the inclusion of air (oxygen) should be avoided. All containers, pipework and valves must be free from heavy metals, particularly copper. Therefore no brass fittings should ever come into contact with fats. This is because these metals act as catalysts for the oxidation process. The products of fat oxidation also catalyse the oxidation so that fats should be stored in clean containers or tanks. The use of clean very hot water is recommended to clean the containers since detergents are difficult to remove completely and traces may give off-flavours to fats subsequently filled into the tank. There is another type of rancidity known as hydrolytic rancidity which involves the formation of soaps (saponification) from the fat. Damp alkaline conditions are required for this chemical change to occur but this happens rarely in biscuit fat handling. Fats, oils and butter 41 6.5 Bulk handling of fats It is common to handle fats in bulk as warm liquids, Le. oils. The freshly refined oil is delivered by road tankers and will be at around 50°C. This is pumped into tanks at the factory and must be held at about -5°C to ensure that there is no crystallisation during storage. The tank is kept warm usually by a water jacket since electric heaters can produce very hot areas that may cause unwanted chemical changes in the fat. The oil is pumped from the tank as required and is usually cooled before use in a dough. The way in which this cooling is achieved is described below in Section 6.6. There are certain precautions that should be taken in bulk handling oils. Before accepting a delivery of oil, sampling should ascertain that the material is both of the type expected and that its quality is satisfactory in terms of taste and certain other chemical characteristics. Ideally the delivery should be filled into an empty and clean tank. In this way contamination with old oil is avoided. There must be a filter in the pipeline between the tanker and the tank and this filter must be cleaned before use and examined after the delivery is complete. It is not unknown for some very unpleasant matter to have become included with the fat and it is important to know about this before the oil is used for making food. The process of oil refining involves the use of fine materials which may not have been completely removed. These materials are harmless but as oil is held in the tank there will be sedimentation. It is therefore necessary to design the tank with a sloping floor and to draw off the oil from the high end of the floor. In this way sedimented matter does not pass out of the tank. In the course of tank cleaning with hot water as described above, the washings must be drained off from a valve at the lowest point of the tank floor and any sedimented material will be taken away with the cleaning water. The sloping floor will also ensure that any water left after washing collects in a place where it will not be drawn off with oil. Since water is heavier than oil it will remain at the bottom of the tank. As the tank of oil is emptied a film of oil is left on the tank walls. Because this is warm and exposed it is particularly prone to 42 Biscuit, cookie and cracker manufacturing manuals oxidation. Cleaning will remove this film and avoid contamination of a subsequent filling of oil. Ideally the headspace of the tank of oil should be filled with an inert gas like nitrogen. Even by observing all these precautions, rancidity cannot be avoided. It is therefore important to use bulk oil as fresh as possible and in'no case to hold it for more than two or three weeks. 6.6 Plasticised and boxed fat It is not normally possible to use liquid oil, either warm or cold, in a biscuit dough mix because the structure of the dough is affected by the rapid coating of the flour by liquid oil. Therefore bulk- handled oil must be cooled before use. Oil is a mixture of chemical compounds known as glycerides. Each different glyceride melts at a different temperature giving the fat a wide temperature range between the point at which crystallisation starts and the point at which all the fat is solid. This makes it difficult to cool an oil because the solid fractions will collect on any cold surface and affect the cooling process. Oils, therefore, have to be cooled in a machine which continuously scrapes the cooled surface. The machine is known as a scraped surface heat exchanger (see Fig. 2). The process is further complicated because if a very cold surface is used to speed the throughput of the oil, there is a tendency for the oil to become supercooled. This means that the oil is still liquid because crystals are slow to form. Within a few minutes of leaving the cooler most of the crystals will have formed and if the liquid is not kept agitated the whole will set into a hard solid or semi-solid mass because the crystals form an interlocking matrix. Therefore, as part of the cooling process agitation must be introduced to ensure that the crystals are broken up as they form and the fat, which is a mixture of solid and liquid fractions, remains plastic and pumpable. This process, where the crystals are broken as they form, is known as plasticising. Thus, a plasticised fat is one which has been cooled to the desired temperature (about 26°C) and the crystals have been broken so that they are all small within the semi-solid mass. Crystallisation of a cooled fat is not complete for some time and it is normal to store plasticised fat for about 24 h before use. It is probable that this is not a critical procedure. A plasticised fat at about 26°C can be pumped to a mixer or filled Fats, oils and butter 43 into boxes which on subsequent slight cooling will not be too hard. In order to handle fat from boxes the temperature needs to be in the range 18-23°C. If it is too warm it will be too fluid to handle and if it is too cold (or well plasticised) it will be hard and not disperse well in the dough mix. Boxed fats normally appear very white. In the process of chilling and plasticising small quantities of nitrogen may be introduced to enhance this white appearance. Inclusion of a gas may help the plasticity slightly but has no known advantage in the biscuit dough. Most dough fats are chosen to have physical characteristics similar to butter. This means that they have a relatively wide melting range, are semi-solid at ambient temperature and are almost completely melted at blood heat. Fats such as palm oil and beef fat can be used as straight fats for biscuit doughs but it is normal to use blends which can involve many different fats of both animal, fish and vegetable origin. Selective hardening and other technical procedures can give blends with the desired physical characteristics. Margarines are made by a similar chilling and plasticising method but they start with a blend of oils, emulsifiers and a water phase which often contains milk solids. It is very unusual for biscuit manufacturers to include water with their fats during chilling and plasticising and boxed fat is normally pure fat without water so that technically it is not a margarine. 6.7 Sandwich cream fats Sandwich cream fats are normally selected for their special melting properties. Sandwich creams for biscuits, which are principally mixtures of sugar and fat, should remain hard at ambient temperature but should melt rapidly in the mouth to release the flavour of the sugar and other components. It is possible to use fats which have a much shorter melting range and are harder (have more crystals) at ambient temperature than typical dough fats. The commonest of these fats are coconut oil and palm kernel oil. By selective hardening these oils can be modified to make them suitable for use in the high temperature ambient conditions that occur in hot countries and in the summer in temperate climates. The short melting range and relatively high solids contents at ambient temperatures makes it difficult to cool and plasticise these fats. 44 Biscuit, cookie and cracker manufacturing manuals 6.8 Spray oil fats Many cracker biscuits are sprayed with oil immediately after baking. This improves the appearance of the biscuits and modifies the eating quality. The fat used for spraying must be selected with care. On the surface of biscuits the fat is exposed to the air and hence to oxidation. The technique of spraying also is conducive to oxidation changes as the oil is hot and the droplets are small and have a great surface area. Fats which are resistant to oxidative change should be used. The cheapest and among the best are the same fats that are used for sandwich creams, coconut oil and palm kernel oil. The fats are sprayed warm and the fact that they are solid at ambient temperature is not important as the film on the biscuit surface does not set to an obvious crust. However, if higher melting types are used there is a tendency for the fat to set and cause adhesion to touching biscuits when packed in columns. The adhesion may result in damage to the thin surface of the biscuits as they are separated before eating. 6.9 Use of emulsifiers and antioxidants Before leaving the complex and important subject of fats and oils, mention should be made of the additives that are commonly associated with fats. Fats and water are not miscible. Thus when doughs are made it is necessary for vigorous action to ensure that the fat is present as very small globules in a flour and sugar system that has an aqueous phase. It is possible to improve the dispersion of the fat in the aqueous phase by using a chemical that has both water and oil solubility characters. Chemicals with these properties are called surface active agents and range from those that promote the dissolution of fats in water, known to us as detergents, and those that promote the dispersion of water in fat, commonly called emulsifiers. Fats in a biscuit recipe contribute to the soft eating nature of the baked biscuit. They make the dough shorter, less extensible and the biscuit softer because less water is needed to make the dough. For this reason dough fats are sometimes referred to as shortenings. By using a small quantity of an emulsifier the fat is dispersed in the dough better and the shortening effect is significantly improved. It is common to find that using an emulsifier can reduce the quantity of Fats, oils and butter 45 fat needed by 10% or more to achieve a similar biscuit eating quality to a dough which contained no emulsifier. The most commonly used emulsifier in biscuits is lecithin which is derived from soya beans. Lecithin used in its plasticised form, which is a thick syrupy material, is often best added to the dough fat before it is cooled and plasticised. In this way the dispersion through the fat, and thence in the dough, is optimised. It is however possible to add lecithin, or other emulsifiers, directly to the dough in either the fluid or powder form. Margarines which contain water usually have an emulsifier added at the time of manufacture. It is not necessary to add more emulsifier when this form of fat is used to make a dough. Attention has been drawn above to the potential problems of fat rancidity on biscuit quality. Precautions have been listed to reduce the incidence of rancidity. In fact, precautions will not prevent rancidity occurring, they will merely retard the onset. It is also common to use chemicals known as antioxidants to retard the onset of rancidity. There is a range of antioxidant materials and all are strictly controlled by food legislation. If fats are handled correctly the use of antioxidants offers little advantage. They may be useful if the fat bulk handling facilities or the biscuit packaging systems are poor. Prevention of the onset of rancidity is most important. Therefore it is recommended that if antioxidants seem to be necessary, they be added by the fat manufacturer immediately the fat is refined and not into the biscuit dough.