Sugar (see below for etymology) is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple (in maple syrup), and in many other sources. It forms the main ingredient in much candy. Excessive consumption of sugar has been associated with increased incidences of type 2 diabetes, obesity and tooth decay.

In non-scientific use, the term sugar refers to sucrose (also called "table sugar" or "saccharose") — a white crystalline solid disaccharide. In this informal sense, the word "sugar" principally refers to crystalline sugars.

Humans most commonly use sucrose as their sugar of choice for altering the flavor and properties (such as mouthfeel, preservation, and texture) of beverages and food. Commercially produced table sugar comes either from sugar cane or from sugar beet. Manufacturing and preparing food may involve other sugars, including palm sugar and fructose, generally obtained from corn (maize) or from fruit.

Sugar may dissolve in water to form a syrup. A great many foods exist which principally contain dissolved sugar. Generically known as "syrups", they may also have other more specific names such as "honey", molasses or treacle.

Scientifically, sugar refers to any monosaccharide or disaccharide. Monosaccharides (also called "simple sugars"), such as glucose, store chemical energy which biological cells convert to other types of energy.

In a list of ingredients, any word that ends with "-ose" (such as "glucose", "dextrose", "fructose", etc.) will likely denote a sugar. Sometimes such words may also refer to any types of carbohydrates soluble in water.

Table sugar (sucrose) comes from plant sources. Two important sugar crops predominate: sugarcane (Saccharum spp.) and sugar beets (Beta vulgaris), in which sugar can account for 12% to 20% of the plant's dry weight. Some minor commercial sugar crops include the date palm (Phoenix dactylifera), sorghum (Sorghum vulgare), and the sugar maple (Acer saccharum). In the financial year 2001/2002, worldwide production of sugar amounted to 134.1 million tonnes.

The first production of sugar from sugarcane took place in India. Alexander the Great's companions reported seeing "honey produced without the intervention of bees" and it remained exotic in Europe until the Arabs started cultivating it in Sicily and Spain. Only after the Crusades did it begin to rival honey as a sweetener in Europe. The Spanish began cultivating sugarcane in the West Indies in 1506 (and in Cuba in 1523). The Portuguese first cultivated sugarcane in Brazil in 1532.

Beet sugar comes from regions with cooler climates: northwest and eastern Europe, northern Japan, plus some areas in the United States (including California). In the northern hemisphere, the beet-growing season ends with the start of harvesting around September. Harvesting and processing continues until March in some cases. The availability of processing plant capacity, and the weather both influence the duration of harvesting and processing - the industry can lay up harvested beet until processed, but a frost-damaged beet becomes effectively unprocessable.

The European Union (EU) has become the world's second-largest sugar exporter. The Common Agricultural Policy of the EU sets maximum quotas for members' production to match supply and demand, and a price. Europe exports excess production quota (approximately 5 million tonnes in 2003). Part of this, "quota" sugar, gets subsidised from industry levies, the remainder (approximately half) sells as "C quota" sugar at market prices without subsidy. These subsidies and a high import tariff make it difficult for other countries to export to the EU states, or to compete with the Europeans on world markets.

The United States sets high sugar prices to support its producers, with the effect that many former consumers of sugar have switched to corn syrup (beverage manufacturers) or moved out of the country (candymakers).

The cheap prices of glucose syrups produced from wheat and corn (maize) threaten the traditional sugar market. Used in combination with artificial sweeteners, they can allow drink manufacturers to produce very low-cost goods.

Since the 6th century BC cane sugar producers have crushed the harvested vegetable material from sugarcane in order to collect and filter the juice. They then treat the liquid (often with lime (calcium oxide)) to remove impurities and then neutralize it. Boiling the juice then allows the sediment to settle to the bottom for dredging out, while the scum rises to the surface for skimming off. In cooling, the liquid crystallizes, usually in the process of stirring, to produce sugar crystals. Centrifuges usually remove the uncrystallized syrup. The producers can then either sell the resultant sugar, as is, for use; or process it further to produce lighter grades. This processing may take place in another factory in another country. Sugar cane appears fourth in the list for agriculture in China.

ICUMSA 45 sugar can be created from either sugar beet or sugar cane. In both cases, the product that undergoes refining is a sugary liquid, but the means of extracting this liquid varies depending on whether sugar beet or sugar cane is used. Extracting sugar juice from sugar beets is the more laborious process of the two, and involves slicing the beets thinly and then putting them into a diffuser, where they are exposed to hot water rushing over them for an hour. The sugar in the beets dissolves into the hot water, and is carried away as sugar juice.

Extraction of sugar juice from sugar cane is somewhat easier, as sugar cane contains enough water to create a juice to begin with, so sugar cane is simply crushed through rollers, and the raw juice spills out and is collected.

This raw juice can be boiled or evaporated to drive the unwanted liquid off the sugar crystals. The raw sugar which results from this process is a very deep brown color and is full of contaminants. This raw sugar can be sold to refineries as is, or it may undergo some processing to create VHP raw sugar, which is still not suitable for human consumption, but which contains fewer contaminants and has a greater sucrose concentration.

At the refinery, raw sugar is refined by a process called ‘affination’. This involves taking the raw sugar and mixing it with a syrup which is also high in sugar. The mixture is called ‘magma’, and is sent into a spinning centrifugal chamber where the liquid is spun away from the crystals, leaving just the crystals behind, minus many of the contaminants. If a refinery is working with VHP sugar, then affination may not be necessary.

In either case, the next stage is a process known as carbonization. Sugar crystals are mixed with water in a 1:1 ratio, and milk of lime (a term given to a calcium hydroxide suspension) and C02 (carbon dioxide) gas are introduced into the solution.

Three major changes are affected in the sugar solution during this carbonation process

Glucose and fructose are destroyed.

Proteins present in the sugar juice are coagulated.

The calcium carbonate created during the process absorbs the compounds which color the sugar, as well as many other microscopic contaminants.

This process can take anywhere from half an hour to an hour, depending on the amount of sugar juice being carbonized, and how refined the sugar will be when the process is finished. During the process, the calcium carbonate sinks to the bottom along with the impurities and colorants and is removed, leaving the purified sugar rich juice on the top.

The sugar juice is then taken to another tank, where is is boiled. The boiling process removes water from the juice, and creates conditions where sugar crystals begin to form. The resulting crystals are once more sent into a centrifugal chamber before being dried and prepared for sale as refined sugar.

Of course, this is a fairly simplistic explanation of the process of sugar refining, and the actual processes undertaken are significantly more involved and carefully controlled.

There are several methods of refining, which are named for the companies which developed them. The most popular methods are the Dorr method, in which refining takes place in two tanks. This is the most often used method in the United States, and the United Kingdom. Another method popular in Europe is the DDS method, which is a multistage process in which the sugar solution is filtered from contaminants after each stage.

Beet sugar producers slice the washed beets, then extract the sugar with hot water in a "diffuser". An alkaline solution ("milk of lime" and carbon dioxide from the lime kiln) then serves to precipitate impurities (see carbonatation). After filtration, evaporation concentrates the juice to a content of about 70% solids, and controlled crystallisation extracts the sugar. A centrifuge removes the sugar crystals from the liquid, which gets recycled in the crystalliser stages. When economic constraints prevent the removal of more sugar, the manufacturer discards the remaining liquid, now known as molasses.

Cane versus beet

Little perceptible difference exists between sugar produced from beet and that from cane. Chemical tests can distinguish the two, and some tests aim to detect fraudulent abuse of European Union subsidies or to aid in the detection of adulterated fruit juice.

The production of sugarcane needs approximately four times as much water as the production of sugar beet, therefore some countries that traditionally produced cane sugar (such as Egypt) have seen the building of new beet sugar factories recently[update]. On the other hand, sugar cane tolerates hot climates better. Some sugar factories process both sugar cane and sugar beets and extend their processing period in that way.

The production of sugar results in residues which differ substantially depending on the raw materials used and on the place of production. While cooks often use cane molasses in food preparation, humans find molasses from sugar beet unpalatable, and it therefore ends up mostly as industrial fermentation feedstock (for example in alcohol distilleries), or as animal feed. Once dried, either type of molasses can serve as fuel for burning.

So-called raw sugars comprise yellow to brown sugars made by clarifying the source syrup by boiling and drying with heat, until it becomes a crystalline solid, with minimal chemical processing. Raw beet sugars result from the processing of sugar beet juice, but only as intermediates en route to white sugar. Types of raw sugar include demerara, muscovado, and turbinado. Mauritius and Malawi export significant quantities of such specialty sugars. Manufacturers sometimes prepare raw sugar as loaves rather than as a crystalline powder, by pouring sugar and molasses together into molds and allowing the mixture to dry. This results in sugar-cakes or loaves, called jaggery or gur in India, pingbian tang in China, and panela, panocha, pile, piloncillo and pão-de-açúcar in various parts of Latin America. In South America, truly raw sugar, unheated and made from sugarcane grown on farms, does not have a large market-share.

Mill white sugar, also called plantation white, crystal sugar, or superior sugar, consists of raw sugar where the production process does not remove colored impurities, but rather bleaches them white by exposure to sulfur dioxide. Though the most common form of sugar in sugarcane-growing areas, this product does not store or ship well; after a few weeks, its impurities tend to promote discoloration and clumping.

Blanco directo, a white sugar common in India and other south Asian countries, comes from precipitating many impurities out of the cane juice by using phosphatation — a treatment with phosphoric acid and calcium hydroxide similar to the carbonatation technique used in beet sugar refining. In terms of sucrose purity, blanco directo is more pure than mill white, but less pure than white refined sugar.

White refined sugar has become the most common form of sugar in North America as well as in Europe. Refined sugar can be made by dissolving raw sugar and purifying it with a phosphoric acid method similar to that used for blanco directo, a carbonatation process involving calcium hydroxide and carbon dioxide, or by various filtration strategies. It is then further purified by filtration through a bed of activated carbon or bone char depending on where the processing takes place. Beet sugar refineries produce refined white sugar directly without an intermediate raw stage. White refined sugar is typically sold as granulated sugar, which has been dried to prevent clumping.

Granulated sugar comes in various crystal sizes — for home and industrial use — depending on the application:

Coarse-grained sugars, such as sanding sugar (also called "pearl sugar", "decorating sugar", nibbed sugar or sugar nibs) adds "sparkle" and flavor for decorating to baked goods, candies, cookies/biscuits and other desserts. The sparkling effect occurs because the sugar forms large crystals which reflect light. Sanding sugar, a large-crystal sugar, serves for making edible decorations. It has larger granules that sparkle when sprinkled on baked goods and candies and will not dissolve when subjected to heat.

Normal granulated sugars for table use: typically they have a grain size about 0.5 mm across

Finer grades result from selectively sieving the granulated sugar

caster (or casto) (0.35 mm), commonly used in baking, originally sprinkled from a castor.

superfine sugar, also called baker's sugar, berry sugar, or bar sugar — favored for sweetening drinks or for preparing meringue

Finest grades

Powdered sugar, 10X sugar, confectioner's sugar (0.060 mm), or icing sugar (0.024 mm), produced by grinding sugar to a fine powder. The manufacturer may add a small amount of anticaking agent to prevent clumping — either cornstarch (1% to 3%) or tri-calcium phosphate.

Brown sugars come from the late stages of sugar refining, when sugar forms fine crystals with significant molasses content, or from coating white refined sugar with a cane molasses syrup. Their color and taste become stronger with increasing molasses content, as do their moisture-retaining properties. Brown sugars also tend to harden if exposed to the atmosphere, although proper handling can reverse this.

The World Health Organisation and the Food and Agriculture Organization of the United Nations expert report (WHO Technical Report Series 916 Diet, Nutrition and the Prevention of Chronic Diseases) defines free sugars as all monosaccharides and disaccharides added to foods by the manufacturer, cook or consumer, plus sugars naturally present in honey, syrups and fruit juices. This includes all the sugars referred to above. The term distinguishes these forms from all other culinary sugars added in their natural form with no refining at all.