My Science School

Catalytic cracking is another method of refining crude oil. By applying pressure and heat to some of the heavier fractions obtained by distillation, lighter, more useful fractions are produced.

Cracking in petroleum refining, the process by which heavy hydrocarbon molecules are broken up into lighter molecules by means of heat and usually pressure and sometimes catalysts. Cracking is the most important process for the commercial production of gasoline and diesel fuel.

After distillation, heavy, lower-value distillation fractions can be processed further into lighter, higher-value products such as gasoline. This is where fractions from the distillation units are transformed into streams (intermediate components) that eventually become finished products.

The most widely used conversion method is called cracking because it uses heat, pressure, catalysts, and sometimes hydrogen to crack heavy hydrocarbon molecules into lighter ones. A cracking unit consists of one or more tall, thick-walled, rocket-shaped reactors and a network of furnaces, heat exchangers, and other vessels. Complex refineries may have one or more types of crackers, including fluid catalytic cracking units and hydro-cracking/hydrocracker units. Cracking is not the only form of crude oil conversion. Other refinery processes rearrange molecules to add value rather than splitting molecules.

Alkylation, for example, makes gasoline components by combining some of the gaseous byproducts of cracking. The process, which essentially is cracking in reverse, takes place in a series of large, horizontal vessels and tall, skinny towers. Reforming uses heat, moderate pressure, and catalysts to turn naphtha, a light, relatively low-value fraction, into high-octane gasoline components.

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The main way in which packaging helps to preserve food is by preventing bacteria from contaminating its contents, but modern packaging is very sophisticated. Some foods are vacuum packed, so that plastic wrappings exclude any air from the product. Other kinds of packaging are designed to trap gases such as oxygen, nitrogen and carbon dioxide. Mixtures of these help to preserve different foods and to give them a pleasant appearance. Meats, for example, can be kept pink and fresh-looking. Sometimes you will see that meat looks browner where it touches the packaging. This is because the gases cannot reach it at this point. As these are gases that we breathe in every day, they are perfectly safe.

Because packaging helps to control the immediate environment of a food product, it is useful in creating conditions that extend the storage life of a food. Packaging materials commonly used for foods may be classified as flexible (paper, thin laminates, and plastic film), semi-rigid (aluminum foil, laminates, paperboard, and thermoformed plastic), and rigid (metal, glass, and thick plastic). Plastic materials are widely used in food packaging because they are relatively cheap, lightweight, and easy to form into desired shapes.

The selective permeability of polymer-based materials to gases, such as carbon dioxide and oxygen, as well as light and moisture, has led to the development of modified-atmosphere packaging. If the barrier properties are carefully selected, a packaging material can maintain a modified atmosphere inside the package and thus extend the shelf life of the food product.

Dehydrated foods must be protected from moisture during storage. Packaging materials such as polyvinyl chloride, polyvinylidene chloride, and polypropylene offer low moisture permeability. Similarly, packaging materials with low gas permeability are used for fatty foods in order to minimize oxidation reactions. Because fresh fruits and vegetables respire, they require packaging materials, such as polyethylene, that have high permeability to gases.

Smart packages offer properties that meet the special needs of certain foods. For example, packages made with oxygen-absorbing materials remove oxygen from the inside of the package, thus protecting oxygen-sensitive products from oxidation. Temperature-sensitive films exhibit an abrupt change in gas permeability when they are subjected to a temperature above or below a set constant. These films change from a crystalline structure to an amorphous structure at a set temperature, causing the gas permeability to change substantially.

Food storage is an important component of food preservation. Many reactions that may deteriorate the quality of a food product occur during storage. The nutrient content of foods may be adversely affected by improper storage. For example, a significant amount of vitamin C and thiamine may be lost from foods during storage. Other undesirable quality changes that may occur during storage include changes in color, development of off-flavours, and loss of texture. A properly designed food storage system allows fresh or processed foods to be stored for extended duration while maintaining quality.

The most important storage parameter is temperature. Most foods benefit from storage at a constant, low temperature where the rates of most reactions decrease and quality losses are minimized. In addition, foods containing high concentrations of water must be stored in high-humidity environments in order to prevent the excessive loss of moisture.

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Fossil fuels, which include coal, oil and natural gas, were formed millions of years ago when prehistoric plants and animals died, and their decaying bodies, pressed under layers of rock and earth, became fossilized. Life as we know it would not be possible without fossil fuels. Not only are they burned to supply heat and energy to homes and industry, but by forming the fuel for power stations, they also supply most of the electricity we use. In addition, fossil fuels can be processed to produce many other useful materials, including plastics, dyes and bitumen.

Fossil fuels include coal, petroleum, natural gas, oil shales, bitumen’s, tar sands, and heavy oils. All contain carbon and were formed as a result of geologic processes acting on the remains of organic matter produced by photosynthesis, a process that began in the Archean Eon (4.0 billion to 2.5 billion years ago). Most carbonaceous material occurring before the Devonian Period (419.2 million to 358.9 million years ago) was derived from algae and bacteria, whereas most carbonaceous material occurring during and after that interval was derived from plants.

All fossil fuels can be burned in air or with oxygen derived from air to provide heat. This heat may be employed directly, as in the case of home furnaces, or used to produce steam to drive generators that can supply electricity. In still other cases—for example, gas turbines used in jet aircraft—the heat yielded by burning a fossil fuel serves to increase both the pressure and the temperature of the combustion products to furnish motive power.

Since the beginning of the Industrial Revolution in Great Britain in the second half of the 18th century, fossil fuels have been consumed at an ever-increasing rate. Today they supply more than 80 percent of all the energy consumed by the industrially developed countries of the world. Although new deposits continue to be discovered, the reserves of the principal fossil fuels remaining on Earth are limited. The amounts of fossil fuels that can be recovered economically are difficult to estimate, largely because of changing rates of consumption and future value as well as technological developments. Advances in technology—such as hydraulic fracturing (fracking), rotary drilling, and directional drilling—have made it possible to extract smaller and difficult-to-obtain deposits of fossil fuels at a reasonable cost, thereby increasing the amount of recoverable material. In addition, as recoverable supplies of conventional (light-to-medium) oil became depleted, some petroleum-producing companies shifted to extracting heavy oil, as well as liquid petroleum pulled from tar sands and oil shales. 

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Most of us can recognize hundreds of different flavours if tested blindfold, but food technologists see these as mixtures of four basic flavours: sweetness, sourness, bitterness, saltiness and Umami. Flavour receptors on different parts of the tongue are best at sensing these flavours. You can test this for yourself with a little sugar for sweetness, salt for saltiness, vinegar for sourness and squeezed lemon peel for bitterness, but hold your nose as you test so that aromas do not affect your judgment.

Flavor or taste is the perceptual impression of food or other substances, and is determined primarily by the chemical senses of the gustatory and olfactory system. The “trigeminal senses”, which detect chemical irritants in the mouth and throat, as well as temperature and texture, are also important to the overall gestalt of flavor perception. The flavor of the food, as such, can be altered with natural or artificial flavorants which affect these senses.

A “flavorant” is defined as a substance that gives another substance flavor, altering the characteristics of the solute, causing it to become sweet, sour, tangy, etc. A flavor is a quality of something that affects the sense of taste. Of the three chemical senses, smell is the main determinant of a food item's flavor. Five basic tastes – sweet, sour, bitter, salty and umami (savory) are universally recognized, although some cultures also include pungency and oleogustus (“fattiness”). The number of food smells is unbounded; a food's flavor, therefore, can be easily altered by changing its smell while keeping its taste similar. This is exemplified in artificially flavored jellies, soft drinks and candies, which, while made of bases with a similar taste, have dramatically different flavors due to the use of different scents or fragrances. The flavorings of commercially produced food products are typically created by flavorists.

Although the terms flavoring and flavorant in common language denote the combined chemical sensations of taste and smell, the same terms are used in the fragrance and flavors industry to refer to edible chemicals and extracts that alter the flavor of food and food products through the sense of smell. Due to the high cost or unavailability of natural flavor extracts, most commercial flavorants are "nature-identical", which means that they are the chemical equivalent of natural flavors, but chemically synthesized rather than being extracted from source materials. Identification of components of natural foods, for example a raspberry, may be done using technology such as headspace techniques, so the flavorist can imitate the flavor by using a few of the same chemicals present.

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Believe it or not, it is possible to live without refrigeration. Long before the advent of home coolers and freezers, the problems of food storage and preservation had been solved, but this invaluable knowledge has been largely forgotten by our modern "quick and easy" society. Today, you can learn how to preserve food without refrigeration to save money and have delicious produce all year.

Bacteria that cause food to go bad need certain conditions in which to grow. If they are deprived of those conditions, they may die or be unable to reproduce themselves. One thing that bacteria need is water, so drying foods can help to preserve them. Bacteria cannot reproduce at temperatures below 6°C (39°F) or above 37°C (98°F), so making them hot or cold can prevent them from being active. Canning preserves food by sealing it into a can and then heating it to a high temperature, killing off the bacteria inside. As no more bacteria can enter the can, the food is safe for a long time, until the can is opened. High concentrations of salt or sugar prevent bacteria from being able to use available water, as can acids, so foods such as pickles and preserves are cooked and stored in brine (a mixture of salt and water), vinegar or sugar.

Anyone who cans their own tomatoes, apple sauce, pickles, or jams knows there is a vast difference between their simple preserves and the chemical-laced stuff found at the grocery store. The flavor of home-preserved produce so far surpasses that of the mass-produced stuff, there’s almost no comparison. To get the absolute most out of your home harvest or CSA haul, try out traditional methods of food preservation such as fermentation, drying, salt-curing, storage in oil or sugar, and more! These methods are simple, require no fossil fuels, and are just as safe as hot-water-bath canning.

Three methods overwhelmingly dominate the history of food preservation before the industrial age: cellar storage under cool, dark conditions, for certain fruits and winter vegetables (such as root vegetables, tubers, apples, and pears); drying, for fruit; and lactic fermentation for most other vegetables.

Natural-state preservation in a cellar is the most basic way to preserve foods that take well to this method. Although it is possible to dry apples and to lacto-ferment carrots, winter provisions have traditionally relied on apples stored in a cellar in their natural state, and carrots preserved likewise in a root cellar, or in the ground.

Nor is the choice between drying and lactic fermentation made arbitrarily. Experience has shown that dried fruits keep much better than most dried vegetables, retaining more flavor and vitamins due to their natural acidity. It is no coincidence that one of the few vegetables traditionally preserved by drying is the tomato, an acidic fruit-vegetable. As for lactic fermentation, people soon discovered that it was an unsuitable method for most fruit: Everyone knows that when fruit is fermented, we get alcoholic beverages.

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When we read the lists of ingredients on food packaging, they sometimes sound more like a chemistry lesson than a recipe! Nowadays, food safety regulations and the demand of consumers for products with a reliable taste and texture mean that many different additives are found in some foods.

Additives perform a variety of useful functions in foods that consumers often take for granted. Some additives could be eliminated if we were willing to grow our own food, harvest and grind it, spend many hours cooking and canning, or accept increased risks of food spoilage. But most consumers today rely on the many technological, aesthetic and convenient benefits that additives provide.

To Maintain or Improve Safety and Freshness: Preservatives slow product spoilage caused by mold, air, bacteria, fungi or yeast. In addition to maintaining the quality of the food, they help control contamination that can cause food borne illness, including life-threatening botulism. One group of preservatives -- antioxidants -- prevents fats and oils and the foods containing them from becoming rancid or developing an off-flavor. They also prevent cut fresh fruits such as apples from turning brown when exposed to air.

To Improve or Maintain Nutritional Value: Vitamins and minerals (and fiber) are added to many foods make up for those lacking in a person's diet or lost in processing, or to enhance the nutritional quality of a food. Such fortification and enrichment has helped reduce malnutrition in the U.S. and worldwide. All products containing added nutrients must be appropriately labeled.

Improve Taste, Texture and Appearance: Spices, natural and artificial flavors and sweeteners are added to enhance the taste of food. Food colors maintain or improve appearance. Emulsifiers, stabilizers and thickeners give foods the texture and consistency consumers expect. Leavening agents allow baked goods to rise during baking. Some additives help control the acidity and alkalinity of foods, while other ingredients help maintain the taste and appeal of foods with reduced fat content.

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In order for a cake to rise and become light and spongy, air has to be trapped inside the mixture, just as it does in bread. Instead of yeast, most cakes contain a raising agent, such as bicarbonate of soda. When it is heated with flour and liquid, chemical reactions take place to produce little bubbles of carbon dioxide, which are then trapped in the mixture as it becomes firm. Another way of incorporating air into cakes is to whisk eggs before adding them to the mixture. The air is trapped in the egg mixture, which becomes firm as it cooks. This method is used in cakes that do not contain fat.

Basically, the thing that makes a cake rise is bubbles, and lots of tiny little ones. You get the bubbles in there with a chemical raising agent like baking powder or by whisking up egg whites. Most recipes will use a chemical raising agent because it’s a lot more predictable and a lot less hard work than whisking for 3 years.

Did you know that cooking is essentially a chemical process that changes the form of your food into one that tastes good? Find out about how chemicals such as Potassium Nitrate and Liquid Nitrogen can be used in cooking and explore its impact on food items like cake.

Baking soda or sodium bicarbonate (NaHCO3) is the active ingredient that is added to baked goods to make them rise. Recipes that use baking soda as a leavening agent also contain an acidic ingredient such as lemon juice, milk, honey or brown sugar which server as a reactive agent. The baking soda reacts with the acidic ingredient to produce tiny bubbles of CO2 that get trapped in the batter.

The gas bubbles expand in the heat of the oven and rise up, giving you a fluffy and airy cake.

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Yeast is a single-celled living organism that digests starches and gives off carbon dioxide gas in the process. Bread can be made light and airy by mixing yeast into the flour and water that make up bread dough. The dough is then left to rise in a warm place. The warmth encourages the yeast to give off tiny bubbles of carbon dioxide, which are trapped within the elastic dough. When the dough is put into the oven, some water evaporates from the flour mixture, and the dough becomes firmer, with the tiny bubbles trapped within it.

Yeast is a tiny plant-like microorganism that exists all around us – in soil, on plants and even in the air.  It has existed for so long, it is referred to as the oldest plant cultivated by man.

Yeast works by serving as one of the leavening agents in the process of fermentation, which is essential in the making of bread.  The purpose of any leavened is to produce the gas that makes bread rise.  Yeast does this by feeding on the sugars in flour, and expelling carbon dioxide in the process.  As the yeast feeds on the sugar, it produces carbon dioxide.  With no place to go but up, this gas slowly fills the balloon.  A very similar process happens as bread rises.  Carbon dioxide from yeast fills thousands of balloon-like bubbles in the dough.  Once the bread has baked, this is what gives the loaf its airy texture.

There are two types of dry yeast:  Regular Active Dry and Instant Yeast (also known as Fast-Rising, Rapid-Rise, Quick Rise, and/or Bread Machine Yeast).  The two types of dry yeast can be used interchangeably. The advantage of the rapid-rise is the rising time is half that of the active dry and it only needs one rising.

You can speed up standard yeast bread recipes by changing the yeast in the recipe.  Substitute one package Instant or fast-acting yeast for one package regular active dry yeast.  Instant yeast is more finely ground and thus absorbs moisture faster, rapidly converting starch and sugars to carbon dioxide, the tiny bubbles that make the dough expand and stretch.

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There are several reasons why food is cooked. Most obvious is the fact that cooking makes food hot! In cold weather, hot food is especially warming and comforting. Cooking also alters the flavour and texture of food. Heat causes chemical reactions to take place, altering the way that the food tastes and feels in our mouths. Because of these chemical reactions, cooking may also make food easier to digest. Finally, cooking can make food safer to eat by killing bacteria within it.

People cook food for many different reasons and while it is best to eat some foods raw such as fruits and vegetables, there are some advantages to cooking food. Food can be cooked for the following reasons:

1. To change or improve the taste of the food e.g. flour being used to make cake. A cake tastes far more delicious than raw flour. Another example includes cooking sugar to make browning used to stew meats. The sugar is no longer sweet but its new taste is desirable when cooking beef etc.


2. To change or enhance the appearance of the food e.g. using rice to make fried rice, preserving mango to make jam


3. To change the texture (the way something feels) of food e.g. using cornmeal to make pastilles. Raw cornmeal is very grainy and coarse but when it is cooked with a liquid it becomes softer, smoother and more palatable.


4.  To make food safer to consume (eat). A good example of this can be found in our where eggs are cooked to make devilled eggs. Raw meat, fish, poultry and egg should all be cooked to make them safe to consume since they contain bacteria that can be harmful to us. For instance, eating raw eggs can cause Salmonella poisoning whose symptoms include vomiting and diarhoea, nausea and general ill health.


5.  To make foods more digestable e.g. tough cuts of meat, hard staples such as rice and cassava. Cooking these foods makes it easier for the body to use it and get all the nutrients from it.


6. To increase the shelf life of the food e.g. making jam from guava. Adding sugar and heating the guava to make jam will make a product that has a longer shelf life than fresh guavas.

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