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.
Once RH exceeds 60%, the water activity (aw) of the gummy surface rises above ~0.65-0.70, causing the gelatin matrix to soften and surface moisture to accumulate. This results in tackiness, adhesion to packaging, and microbial risk.
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) have lower molecular weight sugars, which bind water less tightly. This lowers the sticky threshold to around 50-55% RH. Exceeding 55% RH quickly leads to stickiness.
- Sucrose-dominant formulas (e.g., >60% sucrose) are less hygroscopic. The sticky threshold rises to approximately 60-65% RH, giving a wider processing and storage window.
2. Invert Sugar or Glucose Syrup
- Invert sugar (from hydrolyzed sucrose) is highly hygroscopic, shifting the boundary down to 45-50% RH. Gummies with high invert sugar become sticky much sooner than those with pure sucrose.
- Glucose syrup (with higher molecular weight) can raise the threshold slightly, allowing for over 60% RH before stickiness appears.
3. Sugar Alcohols (e.g., Maltitol, Isomalt)
- In sugar-free gummies, sugar alcohols behave differently. Maltitol is less hygroscopic than HFCS but more than sucrose. The sticky boundary is typically **50-55% RH**. Isomalt, being even less hygroscopic, can push the threshold to 58-62% RH.
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.