In making candy or sugar syrups, sucrose is boiled in water with a little acid, such as lemon juice. Why does the product mixture taste sweeter than the starting sucrose solution?

Understanding the concept of relative sweetness helps explain why some sugars taste sweeter than others. Relative sweetness is a comparison scale, with sucrose traditionally set at 1 as the baseline for sweetness. This scale is useful in the food industry for formulating recipes and creating products with desired sweetness levels without solely depending on sucrose.

Other sugars are measured against this benchmark. For instance, glucose, also known as dextrose, has a relative sweetness of about 0.74, meaning it's less sweet than sucrose. On the other hand, fructose boasts a relative sweetness of approximately 1.7 to 1.8, making it considerably sweeter than sucrose. This disparity is significant when manufacturers wish to increase sweetness while controlling for calorie content or achieving specific flavor profiles.

It's intriguing to note that this measure is subjective and varies depending on individual tastes and cultural background, yet it remains a vital tool for the food industry to standardize sweetness.

The hydrolysis of sucrose is a chemical process where the disaccharide sucrose splits into two monosaccharides, glucose and fructose, in water. The reaction is represented by the equation: \[ C_{12}H_{22}O_{11} \text{(sucrose)} + H_2O \text{(water)} \rightarrow C_6H_{12}O_6 \text{(glucose)} + C_6H_{12}O_6 \text{(fructose)} \].

This transformation occurs commonly in making confections or syrup, where the sweetness profile changes as the reaction progresses. By understanding this reaction, one can see why the resulting syrup is sweeter than the original sucrose solution.

The hydrolysis is favored by heat, and as the temperature rises, the sucrose molecules are more likely to encounter water molecules, making the reaction proceed more quickly. Without keen control over this process, the hydrolysis can lead to crystallization issues or even an overly sweet product, which may not be desired.

An acid catalyst can substantially speed up the hydrolysis of sucrose. In the absence of a catalyst, sucrose hydrolysis would be a much slower process, unsuitable for many culinary applications. Adding a bit of acid, like lemon juice or cream of tartar, provides the necessary acidic environment to enhance the rate at which sucrose molecules interact with water.

The role of acid in this reaction is to donate protons (H⁺ ions) that facilitate the breaking of the glycosidic bond in sucrose. These protons essentially make the water molecule more reactive, turning it into a hydronium ion (H₃O⁺), which is a much more effective nucleophile and can attack the sucrose molecule efficiently, resulting in glucose and fructose.

Acid-catalyzed reactions are crucial in various food processes and not just for altering sweetness. They're used to preserve food, enhance flavors, and aid in the production of certain textures, demonstrating the versatile importance of such catalysis in food science.