Candy moisture activity: Although candy moisture can display the final residual water content of the finished product, it is not sufficient to indicate the state and properties of moisture in the fruit. For example, toffee and fucoidan have similar composition and moisture content, but undergo different changes during storage. The former tends to absorb external water vapor and become sticky and softened, while the latter tends to release water to the outside and become dry, hard, and coarse.

For example, gummy candies with high moisture content can have a much longer shelf life than soft cheese or fondant candies with low moisture content. Hard candies and chocolates with low moisture content often spoil during their shelf life. It can be seen that the meaning of moisture lacks scientific guidance for candy production and preservation. In order to demonstrate the role of water in food, modern food science research has shown that the more important effective standard for food is water activity. Using the concept of water activity to illustrate many issues in candy production practice is also of great significance.

Generally, candies are not processed and packaged under sterile conditions, and spoilage caused by microbial activity is also unacceptable. Research on microorganisms has long found that food moisture is an important factor in promoting their growth and reproduction. The general rule is that foods with high moisture content are more prone to microbial spoilage than those with low moisture content. However, some gel gums with high water content can be kept for more than one year under general conditions, while those with low water content, such as fondant, fondant and chocolate candy, are often spoiled due to microbial action. Food microbiology points out that microorganisms can utilize the free water in food, that is, the available water.

Therefore, using the Aw of food to illustrate this relationship will be clearer. When the Aw value is below 0.9, bacteria can hardly grow. If the Aw value is below 0.88, yeast is inhibited. When the Aw value is below 0.80, most molds also lose their growth ability. Only dry mold and osmotolerant yeast can still develop well at lower Ao values. The Aw of the vast majority of candies is below 0.80, even candies with high moisture content are no exception. This characteristic is very beneficial for candy preservation. It has been determined that pathogenic bacteria cannot grow, and most yeast and mold are also strongly inhibited.

Only dry resistant mold and osmotic pressure resistant yeast are still found in a small portion of candies with high Aw, resulting in fermentation and mold growth, which changes the quality of the candy and damages the value of the food.