Sour Sweets

Adding malic or citric acid to the outside of sweets is a great way to add some zing to your products. But how can you stop an unwanted reaction with sugar?

Unfortunately, the acids can easily absorb moisture and react with sugar, causing it to invert.This can give the appearance that the sugar has “melted”, resulting in unappealing products left in bags, sat on shelves. Let’s take a look at what invert sugar is and how this problem can be solved.

What is invert sugar and what causes it?

Invert sugar has a high rate of water retention and is often used in baking to help reduce the loss of moisture during the baking process. It is sucrose that has been broken down into its constituent parts, glucose and fructose and has a consistency similar to honey.

Sugar can invert by reacting with acid, a process called acid hydrolysis. For this reaction to take place the acid and sucrose molecules need to come into contact with each other. Perfectly dry molecules will take a considerable amount of time to react, however water acts as a fantastic solvent and accelerates the process, forming the sweet liquid known as invert sugar.

How does this impact confectioners?

With sour sweets, sugar is often blended with citric or malic acid and applied to the outside of the sweet. Over time, moisture can either be drawn out of the sweet or from the air (especially in humid climates) providing enough moisture to act as a solvent. The inversion process then continues, causing sweets to look ‘wet’ or ‘sweaty’, with consumers believing them to be past their best and leaving them on the shelf.

However, it isn’t just the appearance that can be affected by this process. One of the reasons we perceive the astringent sourness in acid is due to it absorbing moisture from your mouth. If the acid is already moist then less moisture will be absorbed, leading to less astringency being perceived.

Providing the solution

One of the ways to prevent the inversion process is to encapsulate the acid with vegetable oil before blending it with sugar and coating the sweet. Encapsulation forms a strong barrier or a ‘rain coat’ around the acid particles, protecting them from moisture (see diagram). This prevents the reaction from taking place so the finished products look great, last longer on the shelf and still has the sour zing that consumers expect.

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