There is no single, precise relative humidity (RH) value that universally marks the transition from "pleasantly chewy" to "undesirably sticky" for all gummy supplements. This boundary is highly dependent on the gummy's sugar composition and specific formulation. However, based on industry best practices and our experience at KorNutra, we can provide clear guidelines.
The General Humidity Transition Zone
For most conventional gummy formulations (using corn syrup, sucrose, and gelatin), the critical transition typically occurs within a narrow range:
- Pleasantly chewy: 40-55% RH at 20-25°C (68-77°F).
- Undesirably sticky: Above 60% RH at the same temperature range.
The threshold follows the gummy's own water activity (aw). Soft confectionery gummies typically measure aw 0.45-0.75. A gummy absorbs surface moisture whenever ambient RH climbs above its aw as a percentage, so a product at aw 0.65 stays dry below about 65% RH and tacks above it. The absorbed moisture softens the gelatin matrix into a sticky film, causing clumping, adhesion to packaging, and microbial risk.
Temperature shifts the boundary too. Deliquescence RH falls as temperature rises: at 40°C, sucrose and fructose deliquesce at about 83% and 56% RH, down from 85% and 62% at 25°C. A gummy that holds up in a 20-25°C warehouse can turn tacky at the same RH on a warm day.
How Sugar Composition Shifts the Boundary
The type and ratio of sugars directly alter the gummy's water activity and hygroscopicity (ability to absorb moisture from the air). Here's how common sugar changes affect the sticky threshold:
1. High-Fructose Corn Syrup (HFCS) vs. Sucrose
- HFCS-dominant formulas (e.g., 50-60% HFCS) are rich in fructose, which is far more hygroscopic than sucrose. Crystalline fructose deliquesces at roughly 62% RH at 25°C, so HFCS-heavy gummies turn sticky at lower storage RH than sucrose-based ones.
- Sucrose-dominant formulas (e.g., >60% sucrose) are much less hygroscopic; crystalline sucrose holds out until about 85% RH at 25°C, tolerating a wider humidity window before surface tack appears.
2. Invert Sugar or Glucose Syrup
- Invert sugar (hydrolyzed sucrose, a glucose-fructose mix) is highly hygroscopic because of its fructose, so high invert levels make a gummy go sticky sooner than a sucrose-based formula at the same RH.
- Glucose syrup, especially lower-DE syrup with longer-chain dextrins, is less hygroscopic and shifts the tolerance upward, keeping the surface dry where an HFCS or invert-heavy formula would already be tacky.
3. Sugar Alcohols (e.g., Maltitol, Isomalt)
- In sugar-free gummies, sugar alcohols replace sugar. Crystalline maltitol is low-hygroscopic, taking up meaningful moisture only near 80% RH or above, so it behaves more like sucrose than fructose in storage. Maltitol syrup is more hygroscopic, so behavior depends on which form is used.
- Isomalt is among the least hygroscopic sugar alcohols, taking up almost no water below about 85% RH at 25°C, which makes isomalt-based gummies highly resistant to humidity-driven stickiness.
Practical Takeaway from KorNutra
To manufacture gummies that reliably avoid stickiness, we recommend the following formulation strategies:
- Use a sucrose or isomalt base to keep the sticky boundary above 60% RH.
- Avoid high HFCS or invert sugar levels if you expect storage RH above 55%.
- Always test your specific gummy formula using a water activity meter and controlled humidity chambers. The exact transition point is formulation-specific.
Remember, the environment matters too. For best shelf life, store gummies in airtight containers at ≤50% RH and 20-25°C. At KorNutra, we carefully optimize sugar composition to provide stable, non-sticky gummies for our clients.