If the moisture isn’t right, the circus peanut is a confectionery failure. Too high, and the candies all stick together in the bag and turn mealy. Too low, and they become a rock-hard adhesive that welds jaws together.
But moisture problems aren’t only an issue for the circus peanut. Getting the moisture measurement right is critical for nearly every confectionery product. Water activity is the most powerful way to measure and monitor moisture.

Manufacturing for texture and taste

Many candies have a distinctive texture–chewy, crunchy, smooth, grainy, sticky, or soft. Confectionery flavors are similarly distinctive. These two things come together to form the customer experience.

Moisture plays a key role in the texture of confectionery products. There is an ideal range of water activity that maximizes texture and taste. If product moisture isn’t in the right range, it can ruin entire batches of candy, costing you time and money. Water activity is closely tied to product texture, so it’s easy to set specifications that relate to important texture characteristics.

Water activity is more precise than moisture content

Water activity may also be a more precise moisture measurement. Most candy tends to have relatively low moisture. The circus peanut, for example, has only about 5% by weight. According to the Spangler Candy Company, circus peanut moisture must be between 4.4 and 6.3% to be acceptable. That’s a range of just 1.9%, which would be challenging to measure accurately with a moisture meter.

Fortunately, when moisture changes in products that don’t have much to start with, the water activity reading changes a lot. In a circus peanut, 4.4% moisture is a water activity of 0.450, and 6.3% is 0.600, a total range of 150 water activity units.

Comparing the precision of these two methods, water activity is about 15 times more precise than moisture content.

Water activity predicts moisture migration

Just because your product has the right taste and texture when you box it up doesn’t mean it will stay that way.

Even in a product at rest, water will keep moving from high to low energy. Over time, water will move from a filling into a coating (or vice versa), and the original  product may become gummy, hard, cracked, stale, or otherwise unacceptable. To avoid this problem, adjust and equalize the water activity of different components during formulation to make a product that will keep its character as it waits to be purchased.

Table 1. Average water activity and moisture content readings for common candies

Hit a shelf life target with water activity

Moisture migration isn’t the only factor that affects shelf life. As candy ages, it may lose moisture through the wrapper, eventually becoming rock solid. Understand and predict what will happen over a product’s shelf life by measuring its water activity and the wrapper’s vapor transmission rate. Because water activity is tied to many of the factors that end shelf life, it is an excellent predictor of shelf life. It can also be used in formulation and packaging studies.


Figure 1. Graphical representation of the relationship between moisture content and the average water activity in confectionery products