Functional charac­teristics of sugar

The primary functions of sugar in food products are to provide sweetness and energy.

Our sense of taste can identify four basic tastes: sweet, sour, salty and bitter. The first taste that we encounter (breast milk) is sweet, which may be why a sweet taste is appreciated and interpreted positively. 

Our inherent affinity for sweetness may also be explained by the fact that, in nature, sweet products are rarely poisonous, in contrast to many bitter substances.

The only definition of a sweet taste is that it “tastes like sugar”. Sugar has a uniquely clean sweetness that is entirely free from extraneous tastes or aftertastes.

We cannot measure sweetness. In other words, it is a subjective sensation that is transferred via the gustatory nerves in the taste buds on the tongue and passed on to the brain.

Several factors affect the sensation of sweetness. The concentration of sweetener, temperature, pH value, other ingredients, and the sensitivity of the individual. Subjective factors such as appearance and colour can also affect the sensation of taste.

In order for a substance to taste sweet, it must be water-soluble and its concentration must exceed the taste threshold. In the context of food, sweeteners are often present in concentrations well above the threshold value. To specify the intensity of a sweetener, we therefore calculate the substance’s “relative sweetness”.

Relative sweetness is a measure of how sweet a specific substance is in relation to sugar. We compare different concentrations of a sweetener with a reference solution consisting of saccharose (usually 5 – 10 %). Ordinary sugar has a comparison figure of 1.

All natural varieties of sugar have a low relative sweetness compared with high-intensity sweeteners, which are often several hundred times sweeter than ordinary sugar.

An important property of sugar is that it can strengthen tastes and aromas both above and below the sweetness threshold value.

For example, a small amount of added sugar, can enhance the taste of nutritious, but sour or bitter foods. Sugar’s aroma-enhancing properties are used in a wide range of foods, such as bread and fruit products.

A small amount of added sugar can enhance the taste of cooked vegetables and meat without making them sweet. In other words, we can use sugar as a flavouring in such low concentrations that it falls below the sweet taste threshold value, i.e. below approx. 1 % sugar.

Traditionally, people have added small amounts of sugar to certain cooked-meat products such as ham or liver pâté.

Sugar can affect the weight and volume of food. The volume of liquid is only affected minutely by sugar.

The volumes of bakery products can be affected in various ways.

Sugar increases the volume of savoury bread because the yeast breaks down all or part of the sugar/syrup and transforms it into various components, including carbon dioxide. This carbon dioxide increases the volume of the bread and makes it more porous.

In sweet breads such as sponge cakes and cup cakes, sugar creates bulk – in other words, volume. The sugar still has a physical presence. If we were to stop using sugar in these products, the amount of energy obtained from fat would increase.

The texture of a food contributes significantly to the mouthfeel. In addition to taste and appearance, the mouthfeel also determines whether we perceive the consumption of a food as pleasant.

Sugar affects this by providing volume and consistency in many products such as bread, jam and alcoholic beverages.

In bread, sugar affects the volume of dough by speeding up the fermentation process. This gives the bread a more porous structure and softer crumbs.

In the manufacture of jam, marmalade and jelly, it is important to strike the correct balance between sugar, pectin and acidity. Sugar’s ability to gel when combined with pectin is vital to the consistency of the product. 

Too much sugar may crystallise, while too little sugar will cause the gelling process to fail. If the pH value is too high, the gelling process will be incomplete, whereas if the pH value is too low, the jelly will be unstable and runny.

When combined with the fruit pectin and acids in the correct proportions, sugar brings the jelly, marmalade or jam to the correct consistency. However, certain fruits with very low pectin levels may require added pectin in order to achieve the correct consistency.

Sugar is important in defining the body of beverages, i.e. how filling they are. This affects the sensation in the mouth, and hence the sense of taste.

The preservative properties of sugar are exploited in products such as jams, juices and pickling solutions. 

Foods are preserved to avoid or inhibit the growth of microorganisms that destroy the product and to avoid pathogenic microorganisms that cause diseases.

Microorganisms need water in order to grow. They take on water via the outer layer of the cell. If the concentration of sugar in a product is raised to a certain level, cells are unable to take on water. This inhibits the growth of microorganisms, because the availability of water is reduced and water activity drops. 

Adding sugar to the solution increases the osmotic pressure, thereby reducing the opportunities for microorganisms to grow. By creating the most unpropitious combination of e.g. pH, water activity and temperature for microorganisms, it is possible to reduce the proportion of preservatives. Sugar can play an important role in this.

Since sugar binds water, adding sugar reduces water activity. The less water activity there is, the longer the product will last. Microorganisms can only live in “free” water. If the water activity level is low enough, microorganisms cannot destroy the food.

The fermentation process has been used for centuries to produce or preserve foods.

The fermentation process usually involves the use of yeast and some kind of carbohydrate, e.g. sugar, as an energy source.

In bread making, it is common to add a small quantity of sugar to the dough to kick-start the yeast as it begins creating carbon dioxide. In baking, sugar feeds the yeast; the yeast’s enzymes transform the sugar into alcohol and carbon dioxide. For this reason, sugar is not always present in the end product. 

A little sugar (or syrup) makes the yeast ferment faster and more effectively than when no sugar is added. The carbon dioxide makes the dough swell up and the bread porous.

Sugar affects the freezing point of foods.

The higher the concentration of sugar, the lower the freezing point.

A low freezing point is important in ice cream and frozen desserts. It reduces the risk of large crystals of ice forming. Small ice crystals have a positive effect on the sensation in the mouth, and hence on the taste. 

This effect (lowering the freezing point) is due to the number of molecules per unit of weight. This means that glucose, fructose and invert sugar are more effective than ordinary sugar in lowering the freezing point of foods.

Sugar can give many food products an appetising colour. This may be through caramelisation, the Maillard reaction, or because sugar is able to preserve colour.

The Maillard reaction (a reaction between sugar and amino acids) gives rise to browning and flavouring in products such as bread and coffee. The Maillard reaction is an extremely complex reaction and its end products include pigmentation, which causes coloration and aroma. 

Caramelisation refers to the dehydration of sugar and occurs when a sugar solution is heated to above 100°C. The degree of caramelisation increases as the temperature rises and is dependent on the pH value. 

Sugar molecules are initially broken down, after which the component substances react with one another, with water and with sugar that has not yet been broken down and transform into a mass of delicate brown, sweet-tasting molecules.

Products such as caramel sauce and caramel browning are based on caramelisation.

Caramel browning is a food colorant that is usually manufactured by heating up alkaline sugar solutions to create caramelisation. It is used in soft drinks, beer, confectionery products, soups and sauces.

Sugar ensures that jams and marmalades retain their colour by preventing the fruit from taking on water.

In products such as biscuits and hard caramel, which contain small amounts of moisture water and large amounts of sugar, the relative moisture level is lower than the ambient humidity. Without protective packaging, these products will absorb moisture from the air.

Sugar’s ability to bind water in foods is based on the relationship between crystallised and loose dissolved sugar. Any change in this relationship during production or storage affects the amount of water that the food can bind. Because sugar binds water, reactions that need water are destroyed delayed if sugar is present. The shelf life of bread is extended because sugar causes water to be retained for longer in the bread.

Bread and cakes baked with syrup will be more moist and have a longer shelf life than products made with sugar. This is due to the fructose content of the syrup, because fructose binds more water than sugar.