Water activity (aw) is the main lever we use to keep gummy supplements stable and safe. Low moisture content alone isn't enough: the water has to be bound by ingredients so microbes can't use it.
Understanding Water Activity in Gummies
Water activity measures free water, the water microbes can use to grow. It runs on a scale from 0 to 1, where 1 is pure water. Sugars and humectants bind water in the gummy matrix and lower the aw. That binding is what separates a shelf-stable gummy from one that grows mold in the bottle.
Acceptable Water Activity Levels
For gummy supplements, full microbial inhibition starts below 0.60. Bacteria and most yeasts stop growing well above that, and molds are the last to give in, with a few strains able to survive down to roughly 0.60. We target a range between 0.5 and 0.6 to stay under that line while keeping the texture soft and chewy. As a bottle sits in storage, moisture can migrate between the gummies and the air inside, so a margin below the limit protects the product over its full shelf life.
- Safety margin: the range sits at or below the 0.60 line where molds stop growing.
- Texture: That range keeps the gummy from turning sticky or crystallizing. Go too low and it hardens and turns brittle.
How We Keep It Stable
Controlling water activity comes down to formulation and processing. We use three main levers:
- Formulation: The right mix of sugars (sucrose, corn syrup), humectants like glycerin, and hydrocolloids (gelatin or pectin) binds free water in the matrix.
- Drying: Gummies are cast into starch molds, where the starch draws out moisture as they set, and a conditioning step evens out moisture throughout the piece.
- Packaging: High-barrier, moisture-resistant packaging stops the gummies from picking up humidity in storage.
Measuring and Verifying Water Activity
A target only works if you can measure it. Water activity is read on a chilled-mirror dew point instrument, the standard lab method, which returns a reading in about five minutes, accurate to a few thousandths of an aw unit. We check aw at release and again during stability testing, tracking it alongside moisture content and mold testing, so a batch that drifts above the 0.60 line gets caught before it ever reaches a bottle.
Controlling water activity from production through packaging is how we make sure our gummy supplements stay stable and safe throughout their shelf life.