The Chemistry Behind Sugar

Lucy Bell-Young

by Lucy Bell-Young

11th November 2020

As a staple household item and common food additive, not many of us think about the chemistry behind sugar when this sweet confection is brought up. Instead, images of its fine, crystalline grains, or tightly compacted cubes spring to mind. However, the everyday sugar you add to your cup of tea or baking mix is actually just one of the many types of sugars out there. Chemically, this treasured condiment is known as sucrose, is composed of two simple sugars, and has the chemical formula C12H22O11.

What Is Sugar Made Of Chemically?

All sugars are carbohydrates, which means they are made up of carbon, hydrogen, and oxygen – though the structure varies depending on the complexity of the sugar. As an example, complex sugars, like sucrose, the common table sugar, are composed of two simple sugars: glucose and fructose.

Meanwhile, other types of sugars have different structures and bonds, and this means that not all sugars are chemically the same. For instance, unlike sucrose, lactose is composed of glucose and galactose, while other types of sugars, like maltose, contain two glucose molecules. 

Different sugars on dark table
The chemistry behind sugar depends on whether it is a complex or simple sugar

What Is The Chemical Name For Sugar?

It depends! Sugars have at least 56 names in the English language. While this sounds a little odd, most of these names actually refer to the same thing, and only change depending on where the sugar was sourced from. For instance, fructose is found in all fruits, but its syrup derivatives can have different names depending on the fruits they’re derived from, like grape sugar. The case is the same with sucrose, which is marketed as cane sugar, caster sugar, white sugar, and brown sugar, depending on its composition.

The main difference between different types of sugars is how they’ve been processed. For instance, brown sugar is less refined than white sugar. By being less processed, brown sugar contains less additives and preservatives than white sugar, making it compositionally different and also slightly ‘healthier’. 

Chemically, all sugars are reducible to their simpler constituents. This means they can either be monosaccharides, disaccharides, or polysaccharides. The seven basic simple sugars are:

  • Glucose: This is the main source of energy in biological organisms. Glucose is a simple sugar that’s utilised by cells during the cellular respiration cycle, which has three stages: glycolysi, Krebs cycle (a.k.a. the citric acid cycle), and the electron transport stage. In multicellular organisms like humans, insulin is needed in order for the cells to absorb and utilise glucose.
  • Dextrose: Dextrose is derived from corn and has many medical applications, like treating low blood sugar and preventing dehydration via an intravenous dextrose drip. This sugar is chemically identical to glucose, but the difference in name is used to distinguish it as an aqueous solution of glucose.
  • Galactose: This is a monosaccharide that’s also identical to glucose, this time in terms of formula. The only difference is the position of one hydroxyl group, which is sufficient enough to change the chemical and biochemical properties of the sugar. 
  • Fructose: Fructose is a type of simple sugar commonly found in fruits, vegetables, and honey. Because it’s derived from natural sources, it’s believed that fructose is a healthy source of sugar. In actual fact, consuming too much of this type of sugar can overwhelm the liver and prevent it from metabolising the fructose effectively.
  • Lactose: This is a relatively large sugar molecule that’s commonly found in milk and other dairy products. Lactose is composed of two simpler sugars: glucose and galactose. In order for lactose to be digested and absorbed in the intestines, an enzyme called lactase is necessary to split the two sugars it contains. Some people aren’t capable of producing lactase, which is how lactose-intolerance is developed.
  • Maltose: This is also known as malt sugar, and is commonly found in starchy grains, cereals, wheat, barley, and cornmeal. Maltose is also found in beer because of the fermented hops. It’s a disaccharide composed of two units of glucose with an alpha (α) bond.
  • Sucrose: The most familiar type of sugar is sucrose. This is what we use in our tea and coffee, and while it’s naturally produced in plants, with its most common extraction source being sugarcane, it’s also one of the most refined sugars out there. Sucrose is a disaccharide because it’s composed of glucose and fructose. 
Vector illustration showing chemistry of sucrose
Sucrose is table sugar, making it one of the most common and refined sugars out there

Sugar Chemical Formula

The chemical formula for table sugar, a.k.a. sucrose, is C12H22O11, but this formula changes depending on the type of sugar. This shows how the chemistry behind sugar can vary slightly depending on what you’re working with.

Sugars can be divided into two main categories: simple sugars and complex sugars. The chemical formula of a sugar is therefore determined by its chemical structure and types of chemical bonds. That said, sugars with different structures can be identified by the same chemical formula, such as in the case of galactose and glucose. Here are some common sugars and their chemical formulas:

  • Lactose (C₁₂H₂₂O₁₁): This is the same formula for maltose and sucrose. The structural difference between lactose, maltose, and sucrose is that lactose is composed of one galactose and one glucose molecule, while maltose is composed of two glucose molecules, and sucrose of one glucose and one fructose molecule. 

What Chemical Is Used To Test For Sugar?

There are a few types of chemical reagents that can be used to detect sugars in a solution. These are used as part of a qualitative test for either the presence or absence of sugars in general, or specific types of solutions.

Benedict’s reagent is the most common chemical mixture used for detecting sugars in a solution, though it’s mostly used for detecting the presence of glucose. The way it works is simple, and involves applying heat to the sugar solution that’s being tested. If glucose is present, the Benedict’s reagent will change colour from blue to orange.

This reagent is a complex mixture of sodium carbonate, sodium citrate, and copper(II) sulfate pentahydrate. The standard proportions for this mixture are:

  • Anhydrous sodium carbonate: 100 gm
  • Sodium citrate: 173 gm
  • Copper(II) sulfate pentahydrate: 17.3 gm
Science experiment diagram show Benedict's test for sugar determination with result analysis
Benedict’s reagent is the most common chemical mixture used for detecting sugars in a solution

What Happens When You Heat Sugar?

Depending on the level of heat you apply, sugar will either undergo a physical/phase change or a chemical change. For example, sucrose has a melting point of 186 °C. However, this temperature also triggers the start of combustion in sucrose as water and carbon dioxide are released – so, if you simply want to caramelise sucrose, you should only apply heat up to around 160 °C.

Heat also increases the saturation point of a sugar solution because it excites the molecules in the solvent, meaning that more sugar can dissolve. In turn, more space becomes available for the sugar molecules. If the temperature drops, sugar crystals in a supersaturated solution will thus start to reform.


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