Creating Texture with Water Activity
Water Activity (aW) is typically the measure of a food product being crisp, stale, or soggy. Typically what makes a product interesting and engaging is the texture differentiation between layers or inclusions. A product developer trying to convert a decadent dessert sandwiching crisp inclusions such as pretzels or delicate wafer with fluid caramel sauce can be demanding to ensure each of these components retain their signature textures over the product's shelf life.
By far the simplest recommended solution when combining multi-layer or aggregate components is to develop all semi-completed parts with the same water activity such as aW 0.5. Adjust each segment with the proper humectant balance to retain the desired textural attributes. Aside from selecting packaging, that product is going to be texturally stable.
This is not usually the case at the start of a concept, and shelf stable components including: chocolate, caramel, taffy, nougats, marshmallow, frappe, and dried fruit host water activities between 0.55-0.65. When these components are paired together, even slight moisture discrepancies can detract from desired profile. Each of these examples are primarily sweetened with sucrose which has limitations driven by solubility.
For example, in a candy bar with crisp pretzels, roasted peanuts, and creamy nut butters, the water activity differences are quite minimal and changes over shelf life should be minimal. If only it was always this simple.
For bakery-type inclusions such as cookie bits or pretzels a water activity of approximately 0.3 is the threshold for when our consumers recognize a loss in crispness. Consumers may call with comments citing stale, old, or even “it tastes expired”. Each component maintains individual thresholds for instance peanuts aW of 0.3-0.4 seems ideal (C.M. LEE and A.V.A. RESURRECCION, 2005) Coating low aW ingredients with high viscosity gumming solutions, hydrophobic protein films, lipid-based ingredients like chocolate or stabilized vegetable oils can help form a moderate barrier to the quality degrading changes driven by moisture migration. In tightly organized layer systems moisture will still permeate the thickest chocolate, and moisture always find the slightest pinhole in this layer.
Need help interpreting your product's texture challenges over shelf life?
Frustrated that day one the product was fine and the next day soggy or leathery?
Looking for help selecting the right moisture barrier in your food product?
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