Water Activity and Candy Texture – Hard Hearts
I have always been partial to Sweethearts: chaulky, heart-shaped chunks of candy sold in a box that could alternatively be used for a deck of cards. Perplexed by the needy language that adorns the hearts, I’ve always been content to just munch away on handfuls of them and get my the pastel-colored sugar high.
Recently, though, my work colleagues and I have looked at how texture of products like this is related to water activity. For example, the Sweethearts, as manufactured, start out as a dough that’s shaped into hearts and then baked/dried for 30 minutes. Having never visited the factory, I’m not sure what the water activity is when they’re done. But I’ve had both crunchy (think dry Lucky Charms Marshmallows) and soft. We wanted to know what the dividing line between the two textures was in terms of water activity, and which texture we liked the best.
When we bought some Sweethearts at the store, they were found to be 0.330 aw, and crunchy. After sitting in our bone-dry food lab for a week, they had declined to 0.18 water activity units, and had the mouth feel of ice shards. We then equilibrated the candy chunks over different salt solutions. This brings them to a known water activity, after which we ate some more of them. The verdict: all of us like the softer candies that had a water activity of 0.65 – much higher than the water activity of the product we bought off the shelf. Note that if you live in a rather humid environment (above 60%) you’ll probably find your Sweethearts to be soft, while in the arid farmland of eastern Washington state, ours are usually crunchy.
Where does this leave Sweethearts? With not enough moisture. I recognize that, as a novelty item, Sweethearts may fall into the same category as baseball card gum – the fact that they’re edible is more important than what they actually taste like. Still, the moisture transfer issue is something that Sweethearts scientists must be aware of, since I’ve seen packages covered in plastic wrap before. Our conclusion is this: water activity is the driving force for moisture migration, and moisture migration determines whether we get a nice texture or an unpleasant one. Sounds like a lesson for customers with hard hearts, soft taffy, and everything in between.