What does cooking do to food ? Related: Worksheet Questions -Food- Wh...
Raw foods such as meat, fish and eggs, may harbour food poisoning bacteria, which if consumed are likely to cause illness. The optimum temperature for the multiplication of most food poisoning bacteria is between 5 - 63
o
C, whilst, at temperatures over 70
o
C most bacteria are killed and below 5
o
C most food poisoning bacteria can only multiply slowly or not at all. Most cooking methods if performed properly will heat foods to over 70
o
C, so applying such a temperature for a carefully calculated time period (along with correct food preparation and storage procedures) will prevent many food borne illnesses that would otherwise manifest if the raw food was eaten.
Campylobacter, Salmonella and Listeria monocytogenes are three of the most common food poisoning bacteria and together are reported to affect over 380,000 European Union (EU) citizens each year. Table 1 lists the foods these bacteria are most likely to be found in and the symptoms they commonly cause.
Table 1: Common food poisoning bacteria and their likely food sources and symptoms
Bacteria | Most likely food sources | Symptoms |
Campylobacter | Raw poultry and meat, unpasteurised milk | Fever, headache, diarrhoea |
Salmonella | Raw meat, poultry and eggs, raw unwashed vegetables, unpasteurised milk and dairy products | Fever, diarrhoea, vomiting, abdominal pain |
Listeria monocytogenes | Raw milk, meat, poultry, cheeses (particularly soft, mould-ripened varieties), salad vegetables | Flu-like symptoms, meningitis, septicemia and, in pregnant women, abortion, miscarriage |
1. 2. Digestibility
The fundamental reason we consume food is to extract the vital nutrients that different foods contain to allow our bodies to function properly. This is achieved by digestion, where foods are broken down in the body into a form that can be readily absorbed. However, many of the nutrients contained in foods are not readily accessible prior to cooking and thus, cannot be easily digested by the body. For example, the enzyme amylase (found in the mouth and intestine) breaks down the polysaccharide starch into its monomer glucose constituents, which can easily be digested by the body. Cooking foods containing starch (e.g., cereals and vegetables), prior to consumption initiates the breakdown of the polysaccharide, thus, aiding the action of amylase and the consequent digestibility of the carbohydrate component of the food.
A further discussion of starch degradation can be found later in the review under the heading ‘what happens to food when it’s cooked?
1. 3. Edibility
The desire to eat is primarily driven by the body’s need for nutrition, with the intake of essential nutrients being indispensable for life. This fundamental reason to eat is challenged by the psychological needs of enjoyment and pleasure. Cooking can cause changes in the colour, flavour and texture of foods that allow us to create foods that we derive pleasure from eating. For example, roasting potatoes initiates a series of changes that makes them edible, as well as attractive in colour and taste by generating a golden brown colour, invoking a natural sweetness and producing a crisp shell and a soft internal texture.
For many foods, the cooking process gives them the characteristics we associate with edible food, which are generated through an intricate series of physical and chemical changes that occur when foods are heated. Therefore, without cooking, these changes could not occur and many foods would be deemed inedible.
A detailed discussion of these changes can be found later in the review under the heading ‘what happens to food when it’s cooked?
2. What are the main types of cooking?
The fundamental types of cooking from which cooking methods stem across Europe and indeed, the world, are listed below.
2. 1. Frying
Frying is the cooking of food in oil or fat. Usually, foods that have been fried have a characteristic crisp texture. This is because oils and fats can reach higher cooking temperatures than water, which results in the food being seared. Common types of foods that are fried include; battered or breaded fish or vegetables, crisps, chips and doughnuts.
There are several different types of frying, which vary by the amount of fat / oil required, the cooking time and the type of cooking pan:
- Stir-frying – a frying pan or wok is used to cook foods at a very high temperature, in a thin layer of fat. The food is fried very quickly, during which time it is stirred continuously to prevent the food from burning.
- Deep-frying – a large, deep pan, or deep-fat fryer is half-filled with fat and heated. Food is immersed in the fat for a few minutes, then removed from the fat and drained.
- Shallow-frying – a large, shallow pan is filled with a layer of fat deep enough to cover about one third of each piece of food to be fried. As with deep-frying, the fat is heated prior to the food being added to the pan. After a few minutes cooking, the food is removed from the pan and drained.
Different types of cooking fats/oils for different uses
In general, cooking is carried out in an aqueous environment whereas frying is carried out in oils. In this section, we will focus on the frying performance of common fats and oils as different types of oils are not equally suitable for frying. The choice of oil used in frying depends on taste and on heat stability. Some oils are heat-resistant and can be used at high temperatures, while others with intense flavours and lower heat resistance are best enjoyed raw in salad dressing for example.
When heated, fats are modified by the combination of the oxygen in the air and the increasing temperature. The most visible modifications are an increase of the coloration (browning) and the viscosity, the apparition of foam and the formation of off-flavours. The smoke point of an oil or fat is the temperature at which it gives off smoke. The smoke point generally refers to the temperature at which a cooking fat or oil begins to break down to glycerol and free fatty acids.
Based on their composition, two groups of fats can be defined: saturated and unsaturated fats. Saturated fats are mainly animal fats (e.g. butter, lard) and are solid at room temperature. Some plants fats are also high in saturated fats such as coconut oil and to a lesser extent palm oils. Saturated fats offer a higher temperature and oxidation stability than oils with a high content of unsaturated fatty acids. However, saturated fats are more likely to produce smoke and foam when heated.
Unsaturated oils are found both in animal and plant products. There are two types of fatty acids: monounsaturated and polyunsaturated fatty acids. Properties depend on the precise fatty acid composition. Monounsaturated fatty acids occur abundantly in oils like olive, peanut, and canola/rapeseed. They are liquid at room temperature. Polyunsaturated fatty acids occur at a high level in oils like corn, safflower, sunflower, soybean, cotton seed, and sesame seed oils. They are also liquid at room temperature.
Trans fats are produced when liquid oil is made into a solid fat by a process called hydrogenation. In recent years they have been removed largely from frying oils and fats because of their negative health properties. For health reasons, the ideal cooking oil should contain high amounts of monounsaturated and polyunsaturated fats, with low amounts of or no saturated fats and trans fats as well as a smoke point higher than the cooking temperature (see Table 2).
Table 2: Suitable cooking uses of fats and oils
Fats or Oils | Cooking Uses | Type of Fat | Smoke Point �F | Smoke Point �C |
Almond Oil | Saut�ing, stir fry | Monounsaturated | 420�F | 216�C |
Butter | Baking, cooking | Saturated | 350�F | 177�C |
Butter (Ghee), clarified | Frying, saut�ing | Saturated | 375-485�F (depending on purity) | 190-250�C (depending on purity), |
Canola Oil (Rapeseed oil) | Good all-purpose oil. Salad dressing and cooking. | Monounsaturated | 400�F | 204�C |
Coconut Oil | Coatings, confectionary, shortening | Saturated | 350�F | 177�C |
Corn Oil | Frying, salad dressings, shortening | Polyunsaturated | 450�F | 232�C |
Cottonseed Oil | Margarine, salad dressings, shortening, frying. | Polyunsaturated | 420�F | 216�C |
Grapeseed Oil | Saut�ing, frying, salad dressings. | Polyunsaturated | 392�F | 200�C |
Hazelnut Oil | Salad dressings, marinades and baked goods. | Monounsaturated | 430�F | 221�C |
Lard | Baking and frying | Saturated | 370�F | 182 �C |
Olive Oil | Cooking, salad dressings, saut�ing, pan frying, searing, deep frying, stir frying, grilling, broiling, baking | Monounsaturated | Extra Virgin - 320�F Virgin - 420�F Pomace - 460�F Extra Light - 468�F | 160�C 216�C 238�C 242�C |
Palm Oil | Cooking, flavouring | Saturated | 446�F | 230�C |
Peanut Oil | Frying, cooking, salad dressings | Monounsaturated | 450�F | 232�C |
Sesame Oil | Cooking, salad dressings | Polyunsaturated | 410�F | 232�C |
Shortening, Vegetable | Baking, frying | Saturated | 360�F | 182 �C |
Sunflower Oil | Cooking, margarine, salad dressings, shortening | Polyunsaturated | 450�F | 232�C |
Vegetable Oil | Cooking, salad dressings | Polyunsaturated | | |
Walnut Oil | Saut�ing, pan frying, searing, deep frying, stir frying, grilling, broiling | Monounsaturated | 400�F | 204�C |
2.2 Baking
Baking is the process of cooking foods in the dry heat of an oven. During baking, moisture within the food is converted to steam, which combines with the dry heat of the oven to cook the food. Common types of foods that are baked include; bread, cakes, jacket potatoes, and pastries.
2.3 Boiling
Boiling is the cooking of foods in a liquid (e.g., water, milk or stock), which is at boiling point. Common types of foods that are boiled include; vegetables, rice and pasta.
Blanching is a very similar cooking technique to boiling and involves immersing food into a boiling liquid for a very short period of time, before being removed and plunged into ice water to stop the cooking process. Common types of food that are blanched include; vegetables and fruits.
2.4 Simmering
Simmering is also a similar cooking method to boiling, except that the food is cooked in a liquid, which is held below boiling point. The simmering point of most liquids is between 85-95
o
C, and compared to boiling, is a gentler, slower method of cooking. Common types of foods that are simmered include; vegetables, soups and sauces.
Poaching is a comparable cooking technique to simmering, except that the temperature of the liquid the food is cooked in is slightly cooler than simmering point (around 70-85
o
C). This makes poaching an ideal method of cooking fragile foods such as eggs and fish.
2.5 Grilling
Grilling is the cooking of food using a direct, dry heat. There are several sources of dry heat that may be used for grilling including; charcoal, wood, gas or electric heated grills. Common types of food that are grilled include; fish, meat, vegetables and bread.