Fats and oils are nutritionally useful and some form economical sources of energy and give a satiety value to the dish. They also contribute characteristic palatability, qualities of flavour, and texture and popularly used as the medium of cooking.
The scientific term “Lipid” comprises a group of substances that include natural fats and oils. Both lipids consist of fatty acids and glycerol.
The only difference between fats and oils is that oils are liquid at room temperature (only exceptions are coconut and palm oil), whereas fats are solid as they contain saturated fatty acids. Saturation means the density of fat, in other words, it is the molecular structure of the fat where the carbon atoms are bonded with hydrogen and oxygen.
The saturation is increased artificially by adding hydrogen into fat by a process known as saturation or hydrogenation of fat/oil. For example, oil can be converted into margarine by passing hydrogen into it to make it saturated. This is done to stabilize the fats and oils and therefore the shelf life of the product increases as it does not oxidize easily.
Those fats which are transformed artificially from oil to fats are known as trans-fats and they are not healthy as they are the prime cause of the cardiac disorder.
Fats and oils do not dissolve in water, but they can be emulsified with water to produce salad dressings and sauces. Fats along with carbohydrates and proteins make up the major components of food.
USAGE OF FATS and OILS IN COOKING and BAKING
Fats and oils are the prime ingredients for cooking and baking around the world. Fats and oils give richness, variety of texture, and smoothness to the fat otherwise it may be too dry to eat. The melting and smoking points of fats and oils are very important to the chefs, as they decide the usage of the lipid in the dish, one cannot use butter for deep frying as it has a very low smoking point, so it will burn to black till it reaches the temperature of frying.
Fats and oils are used for various purposes like:
- Spreads – butter and margarine are used for spreads and their function is to add the flavour, nutritional value, and satiety value of bread.
- Shortening – these are fats that shorten the gluten strand by surrounding them and make them more easily broken (short). When added to bread it gives a bit of tenderness, richness, and sheen to the crumb.
- Tempering – spices are added to hot oil/fat and then added to dal, curries, rice, etc. to give better flavour, very common in Indian cuisine.
- Salad dressings – fat is one of the main ingredients of salad dressings: like animal fat dressings like bacon fat, vinegar, and seasonings, or other common dressings like vinaigrette, mayonnaise, etc.
- Flavoured oil/infused oils – nowadays flavoured oils play a vital role in food production, they can be used as salad dressings, garnishes, or simply as accompaniments e.g. Chili oil, basil oil, peppers oil, etc.
- Frying medium – fats and oils are hugely used as cooking medium, i.e. pan roasting, deep-frying, and sautéing. Fats with a high smoking point is better for frying, the highest frying temperature needed for frying anything is 1990C/3900
- Creaming and aerating effect – When making rice cakes, fat and sugar are beaten or creamed together. This process incorporates small air bubbles into the mixture and so lightens the product.
RENDERING OF FAT
Rendering is a process where the fat is melted on heat to separate the skin and non-fatty membrane. This is done over low heat, and sometimes some water is added to it and brings to a boil, then the flame is reduced and let most of the water evaporates leaving behind the clear fat which can be strained and stored away. Another method is to keep the fat on low heat, all the fat will melt out leaving some crisp skin behind, which is known as “crackling” and this can be used for salads and garnishes.
Clarifying butter is a process where the water and the milk solids are removed so that butter becomes more stable and can be used for cooking without changing its properties. This process is very similar to that of the rendering fat.
PROPERTIES OF FAT
- Solubility – Fats and oils are insoluble in water. However, in the presence of a suitable substance known as an emulsifying agent, it is possible to form a stable mixture of fat and water. This mixture is termed an emulsion. The emulsion may be a fat-in-water emulsion, e.g. milk, or a water-in-fat emulsion, e.g. butter.
- Effect of heat – As fats are heated there are three temperatures at which noticeable changes take place.
Melting Point – Fats melt when heated. The temperature at which melting starts is called the Slip point. Most fats melt at a temperature between 30°C and 40°C.
Smoke Point – When a fat or oil is heated to a certain temperature it starts to decompose, producing a blue haze of smoke and a characteristic acrid smell. Most fats and oils start to smoke at a temperature around 200°C. In general, vegetable oils have a higher smoke-point than animal fats. when using fat or oil for deep frying, the frying temperature should be kept below the smoke-point. Smoke-point is a useful measure when assessing the suitability of a fat or oil for frying purposes. Repeated heating of a fat or oil or the presence of burnt food particles will reduce the smoke-point.
Flash Point – When fat is heated to a high enough temperature, the vapors given off will spontaneously ignite. This temperature is known as the flash-point. For corn oil, the flash-point is 360°C. A fat fire should never be put out with water; this will only spread the fire. The heat should be turned off and the oxygen supply cut off by covering the container of burning fat with a lid or blanket.
ANIMAL FATS USED IN COOKING
Lard is pig fat in both its rendered and unrendered forms. Lard was commonly used in many cuisines as a cooking fat or shortening, or as a spread similar to butter. Nowadays the uses of lard are restricted due to health concerns.
Suet is raw beef or mutton fat, especially the hard fat found around the loins and kidneys. Suet has a melting point of between 45° and 50°C. (113° and 122°F.). Its low melting point means that it is solid at room temperature but easily melts at moderate temperatures, such as in steaming. It used to be used for shortcrust pies
Tallow is a rendered form of beef or mutton fat, processed from suet. It is solid at room temperature. Unlike suet, tallow can be stored for extended periods without the need for refrigeration to prevent decomposition, provided it is kept in an airtight container to prevent oxidation.
Butter is a dairy product made by churning fresh or fermented cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications such as baking, sauce making, and frying. Butter consists of butterfat, water and milk proteins.
Most frequently made from cows’ milk, butter can also be manufactured from the milk of other mammals, including sheep, goats, buffalo, and yaks. Salt, flavorings, and preservatives are sometimes added to butter. Rendering butter produces clarified butter or ghee, which is almost entirely butterfat.
Butter is an emulsion that remains a solid when refrigerated, but softens to a spreadable consistency at room temperature, and melts to a thin liquid consistency at 32–35 °C (90–95 °F).
It generally has a pale yellow color, but varies from deep yellow to nearly white. Its color is dependent on the animal’s feed and is commonly manipulated with food colorings in the commercial manufacturing process, most commonly annatto or carotene.
Ghee is made by simmering unsalted butter in a large pot until all water has boiled off and protein has settled to the bottom. The cooked and clarified butter is then spooned off to avoid disturbing the milk solids on the bottom of the pan. Unlike butter, ghee can be stored for extended periods without refrigeration, provided it is kept in an airtight container to prevent oxidation and remains moisture-free. Texture, colour, or taste of ghee depends on the source of the milk from which the butter was made and the extent of boiling.
It is the primary cooking medium of India and in many Arab countries. Flavorings are often added like in India it can be bay leaves, cumin, cloves, turmeric, etc, in Arab herbs like thyme, oregano, etc. can be added.
Schmaltz or schmalz is rendered chicken or goose fat used for frying or as a spread on bread, especially in German, Polish, and Jewish cuisine.
TYPES OF VEGETABLE OIL USED IN COOKING
Obtained from corn or maize, it has a high smoking point of 232oC, thus very useful for deep frying.
Extracted from the seed of a cotton plant, having a high smoking point like corn oil.
Ii can be of two types refine and unrefined, refining increases the smoking point and makes it more suitable for deep frying. The smoking point of this oil is 232oC
Also known as peanut oil, it has a smoke point of 225oC, so good for deep frying
Most widely produced oil worldwide. It is made from the seed of the palm fruit. The presence of Beta carotene gives a red hue, which is faded when heated. It is one of the most stable oil, which is semi-solid at room temperature, so used for making margarine.
The rapeseed tree is a member of the Brassica family, it is used mainly as food for cattle, and the seed is used for making oil. It contains a good amount of omega-6 and 3 so it is considered as healthiest of oils. It is also known as Canola [can-o-la – Canadian oil low acid content].
Very common in India, especially in east India [West Bengal]. This oil is deep yellow in color and has a very pungent smell. It should allow smoking for at least 2 – 3 minutes to allow the pungent flavour to escape. Hugely used to pickle vegetables.
It is made from olives and mainly used in Mediterranean countries; it has a low smoking point of 165oC so not suitable for deep frying. It has huge uses like salad dressings
NUT – BASED OIL
Made from various nuts, like walnut, hazelnut, almond, etc. those oils are suitable for salad dressing or soup garnishes for their very strong flavor, but not suitable for cooking due to their very low smoking point. Those oils may become bitter with the application of heat.
Some vegetables like avocado, pumpkin is often used to make oils to make margarine. Avocado oil is very expensive and used for salad dressing.
Margarine is a generic term that can indicate any of a wide range of butter substitutes. In many parts of the world, the market share of margarine and spreads has overtaken that of butter. Margarine is an ingredient in the preparation of many other foods and in recipes.
Margarine is an emulsion of water in fat. The fat is a blend of refined vegetable oils, a portion of which has been hardened by hydrogenation to produce the desired plasticity in the final product. Fish oils and animal fats may also be incorporated in the blend. The hydrogenation is carried out by heating the oil in large sealed vessels under pressure. Hydrogen is bubbled into the oil and finely divided nickel, which is subsequently removed by filtration, is required as a catalyst. The oil blend is mixed with the water phase, which is skimmed milk, soured under controlled conditions to give the desired flavour to the product. Artificial colouring, salt, and vitamins A and D are then added. In Britain, these vitamins must be added by law. This law is necessary because margarine often replaces butter in the diet and butter is an important source of vitamins A and D. The emulsion is formed in a machine called a votator, in which mixing and cooling occur together, and fat of the desired consistency is produced.
PUFF MARGARINE – Pastry margarine performs better than butter in making puff pastry because of its high melting point. It does not melt quickly, thus allowing time for the puff pastry dough to rise sufficiently high while not making it heavy and soggy. Then as the temperature increases, the pastry margarine will then melt and infuse into the risen pastry, giving it its scrumptious flavor. It is low in moisture content also
CREAM MARGARINE – Has a lower melting point than other varieties of margarine, but solid at room temperature.
CAKE MARGARINE – A moderate melting point with medium moisture content, suitable for cake batters.
Hydrogenation in food industry
Hydrogenation is widely applied to the processing of vegetable oils and fats. Complete hydrogenation converts unsaturated fatty acids to saturated ones. In practice, the process is not usually carried to completion. Since the original oils usually contain more than one double bond per molecule (that is, they are polyunsaturated), the result is usually described as partially hydrogenated vegetable oil; that is some, but usually, not all, of the double bonds in each molecule have been reduced. This is done by restricting the amount of hydrogen (or reducing agent) allowed to react with the fat. Hydrogenation results in the conversion of liquid vegetable oils to solid or semi-solid fats, such as those present in margarine. Changing the degree of saturation of the fat changes some important physical properties such as the melting point, which is why liquid oils become semi-solid. Semi-solid fats are preferred for baking because the way the fat mixes with flour produces a more desirable texture in the baked product. Since partially hydrogenated vegetable oils are cheaper than animal source fats, they are available in a wide range of consistencies, and have other desirable characteristics (e.g., increased oxidative stability (longer shelf life)), they are the predominant fats used in most commercial baked goods. Fat blends formulated for this purpose are called shortenings.