MAINTAINING THE VACUUM

During hot filling, the beverage is filled at an elevated temperature and the bottle is immediately capped. A hot beverage occupies approximately 2–3% more volume than it does at room temperature. As it cools, it contracts, creating a vacuum within the sealed bottle under the cap.

Yeast and mold are naturally present in ambient air. If the cap does not form a tight seal and maintain the vacuum, air can enter the bottle as the liquid cools and contracts, potentially introducing yeast or mold. Hot-filled beverages produced without preservatives rely on a properly sealed bottle for microbial stability. A compromised seal can result in mold growth or fermentation caused by yeast.

Air entering the bottle also introduces oxygen, which can cause oxidation and degrade the product’s flavor, color, and oxygen-sensitive ingredients, including certain nutrients.

When selecting a bottle capable of withstanding hot-fill temperatures—typically 175–180°F—it is equally important to select a compatible closure that will properly seal the bottle and maintain the vacuum throughout the product’s shelf life.

The bottle and closure should be evaluated as a complete packaging system. When selecting a cap for a hot-fill compatible bottle, the manufacturer should certify that the cap:

    •  Is rated for hot filling at the required temperature.

    •  Has a liner that can withstand that temperature without softening, shrinking, or losing compression.

    •  Is designed to maintain the expected vacuum throughout shelf life.

    •  Can withstand bottle inversion while the product is hot.

We can recommend suitable bottles and closures for the safe hot-fill processing of beverages without preservatives.