Food Science: Is it done?
As you cook you will see scientific changes to take place between ingredients. Visual checks are a way to help you notice these changes. You might see colour changes, increase in size, rising, decrease in size, shrinkage, texture changes such as crispness, crustiness or set. Cook and think!
In this booklet we are exploring the browning of foods. It is the key to the question ‘Is it done?’ Browning is affected by several factors such as the length of the cooking time, the types of ingredients being used, the effect of heat on those ingredients, and the change from ‘raw to cooked’ in terms of sensory characteristics.
Is it done? is a concept that raises a set of questions
• Has the cooking time expired?
• Is the texture as required?
• Has it risen?
• Does it smell cooked?
Is it done?
Use this booklet to check your understanding of ingredient characteristics and food science. Practical cooking is the best way to learn food science.
Food science and browning
Sugars and starch turn golden when cooked in dry heat. It is a browning process. Sugar and water will dissolve to form syrup when heated and as the syrup solution becomes stronger so it turns a darker brown. It makes a brittle strand and creates crunch. An example is seen in creme brulée topping.
THE MAILLARD REACTION
This reaction is scientific. It is the combination of reducing sugars and proteins together with heat. It is NOT due to enzyme activity. The Maillard reaction forms melanoids which are brown pigments. An example is the surface of meat after cooking by roasting.
Starch foods change due to heat. The starch turns to dextrins and therefore the process is called dextrinisation. Starch in the form of flour, will turn golden in a hot oven around 180⁰C to 200⁰C (Gas 4 – 6).
Dextrins are sweeter than starch and this improves the flavour of the product whilst also browning it. An example is bread made into toast
Where do we see browning when we cook?
Cooking meat primarily makes it safe to eat and at the same time produces characteristics that consumers enjoy such as tenderness and moistness, a brown colour and a good flavour. The surface of cooked meat browns in the oven as a result of the Maillard reaction. This reaction is scientific. It is the combination of reducing sugars and proteins together with heat. It is NOT due to enzyme activity.
The Maillard reaction forms melanoids which are brown pigments, with a sweeter meaty flavour.
Browning can be as a result of the extreme heat from a BBQ or a griddle pan. This will ‘char’ the surface of meat leaving brown marks. Steaks can be cooked this way. Meat cooked in a stew, hotpot or casserole will not brown. It will become tender and fall apart due to the breakdown of collagen to gelatine during the slow moist cooking. Browning only occurs if the meat is ‘fried off’ prior to being put into the casserole and the stock added.
Pastry turns golden brown when it cooks in the oven at around 200C (Gas Mark 6). Pastry texture changes when it is cooked. Raw pastry is pale and pliable, cooked pastry is crisp, golden and non-pliable. Flour is the main ingredient in pastry. The starchy part turns golden when cooked in dry heat (oven). The protein in the wheat grain called ‘gluten’ is hardened by baking in the oven and is responsible for the change in texture when pastry is cooked. Cooked pastry makes a structure, such as a crust or a base which can support other food ingredients such as in tarts, quiches, pies or rolls.
THE CASE OF THE DISAPPEARING FAT IN PASTRY!
Pastry contains fat. Shortcrust pastry recipe is 50% fat. During cooking the fat melts and is absorbed by the flour. Hence the fat you see as an ingredient disappears during the cooking. Fat is responsible for the yellow colour of the pastry and the short, crumbly texture of pastry. The fat is referred to as invisible fat in the diet because you do not see it.
The colour of a cake is a factor upon which we judge whether it is done. What causes a cake to turn brown? Cakes, composed of SR flour, yellow fat (margarine, butter, oil), sugar and eggs will react with dry heat in an oven and show visible changes. Cakes rise due to the raising agent in the flour. The yellow fat melts and is absorbed by the flour starch giving a yellow colour. Eggs, usually beaten to trap air, help the cake to rise and have a light texture. The egg proteins set and help hold the risen shape of the cake alongside the flour protein, gluten. Sugar keeps the cake texture soft and makes the cake taste sweet. As the cooking time progresses a rich golden brown crust develops on a cake. It is a good indicator that the cakes such as Victoria sandwich, Swiss roll, Rubbed-in cakes or All-in-one mixes, are fully cooked.
Potato is a starchy food that browns well. Browning is more marked when fat is also used. It is seen in roast potatoes, browned potato topping on cottage pie, wedgies, rosti or hash browns.
Browning is a very attractive feature of baked breads, loaves, rolls, croissants, and other bread based products. As with pastry, the main ingredient in bread is wheat flour. Bread however needs to be made from ‘strong wheat flour’ that contains gluten in larger amounts than plain pastry flour. Gluten makes the bread dough stretchy and enables it to rise when gas is produced by yeast or soda. As the temperature rises so the protein, gluten, will set and become firm and ‘hold’ the risen shape. The dry heat of the oven also turns the starch on the dough surface a golden brown and it becomes slightly sweeter. This is known as dextrinisation. A golden crust on bread is an indication that the bread is fully cooked.
A test for a cooked loaf or roll is to tap the base and listen for a hollow sound.
Glazing helps the browning of baked food such as pies, breads and sausage rolls. Egg wash or milk can be used to glaze pastry. Glazing with malt syrup gives bagels a sweeter taste. Glazing with sugar syrup gives a glossy and sweet coating to baked items such as hot-cross buns or baklava.
the end biscuit becomes. Compare chocolate chip cookies to shortbread to see this in action.
Crispbreads are a unique type of biscuit based on grains such as rye, wheat and oats. They contain lower amounts of sugar and fat . Many are enriched with seed toppings and flavoured salts. Crispbreads are baked and therefore their golden brown colour is often an attractive feature.
Meringues are different to other baked goods in that the aim of cooking is merely to dry out the meringue and to retain the white colour of the egg white foam. This is difficult because of the amount of sugar in the recipe which, in the presence of heat, is likely to turn golden. It is essential to cook meringues in a low temperature oven. Baked meringues should remain white. Examples are Pavlova, meringue nests, meringue shells and meringue swans.
Golden colours occur when meringue is ‘flash’ baked in a hot oven or seared with a blow torch. The browning is due to caramelisation. Browned meringue makes an attractive topping as seen in Queen of puddings or baked Alaska.
When grated cheese is sprinkled over a dish it is said to be ‘au gratin’. Grilling or baking the ‘au gratin’ dish produces a brown and crunchy topping. The crunchy golden topping is formed when the heat affects the structure of the grated cheese. Traditionally the type of cheese used for ‘au gratin’ is Cheddar, Leicester or Lancashire. These types of cheese are known as hard cheeses and they contain around one third fat, one third protein and one third water.
The fat melts when the cheese is heated. The exposed cheese proteins will then shrink due to the heat and squeeze out more fat before turning golden brown and becoming tougher in texture. Sometimes breadcrumbs are added to the grated cheese to help the crunchiness of the topping. Examples are Macaroni cheese au gratin, Cauliflower cheese au gratin. Also cheese scones and cheese straws.
A different type of browning can occur during food preparation and serving.
Enzymic browning occurs when the cells of some fruits and vegetable are cut allowing the enzymes to be exposed to the air and become active. This sort of browning is not desirable as it changes the colour of the fruit or vegetable.
How can Enzymic browning be prevented?
Enzyme activity can be delayed by dipping the cut fruit pieces in lemon juice which is too acid for enzymes to continue to work. Alternately the fruit pieces can be immersed in water to stop the air reacting with the enzymes. Pre-prepared fruit salads, sold in supermarkets may have vitamin C (ascorbic acid) added in order to aid an acid level that stops enzyme activity. As a result, the fruit will remain a good colour, look attractive and keep without browning.
Baking is cooking products in dry heat in an oven. Fan ovens blow the heat around therefore all the shelves cook evenly at the same temperature. Baking causes starchy and sugary ingredients to turn a golden-brown colour, known as caramelisation.
Steaming is a moist method of cooking. A steamer tier or stack is placed over boiling water and a top lid traps the steam. If you have more than one layer you can cook broccoli in one layer and carrots in another. This saves fuel, and also makes good use of the hob. Steaming does not generally cause foods to brown.
High-pressure steaming is a moist method of cooking using a pressure cooker.
Frying uses a shallow and flat frying pan with a long handle used on the cooker hob. Frying causes browning where the food touches the pan. This adds flavour and colour to the food. A stir-fry pan is deeper with sides that enable you to stir rapidly and cook over a high heat without browning.
Dry frying is frying using fatty ingredients such as bacon lardons (cubes of bacon), chorizo, or sausages without adding oil or fat. Dry frying extracts oil and fat from the product and uses it to cook and brown the product.
Boiling is cooking in water ‘on the move’ at boiling point (100⁰C) on the cooker hob. Generally
a lid is placed over the pan to retain the heat and keep in the steam. Simmering is a gentle boil with the heat control turned down. Boiling does not cause foods to turn brown.
Grilling is a hot and direct method of cooking. Thin products are best as the heat can penetrate one side and then, on turning, the other side. Grilling creates golden brown colours to starchy or fatty foods, bread becomes toast, streaky bacon turns golden and crisp.