Bubble testing is the simplest, least expensive method of detecting and assessing leaks. The procedure involves creation of a pressure differential across the package with air (or some other gas) on the high pressure side (inside package) and a water chamber on the low pressure side (outside package). Leak detection is performed by immersing the package in a water-filled test chamber. The headspace above the water level is evacuated, which cause the package to inflate. If there's a leak, air or gas flow through leaks will result in the formation of bubbles outside the package. This method provides immediate indications of the existence and location of small leaks.

Disadvantages include a long test time (a minimum of 30 seconds per test), low sensitivity, the tendency of leaks to get clogged by viscous food materials during testing, water contamination, and part clean-up time. The sensitivity of the test is not high, due to operator dependence. The reproducibility and sensitivity of bubble testing depends on the use of a dark background (increased contrast), high pressure differentials, and the operator.

• Vacuum water chamber with a regulator
• Vaucum pump
• Water

1. Fill the chamber with enough water to submerge a package when expanded.
2. Place a package to be tested in the chamber and close the lid.
3. Turn on a vacuum pump and open a regulator valve to generate vacuum inside. 
4. Increase vacuum (up to 30 inHg) until the package is expanded. Bubbles will rise from a leak.
5. When testing is complete, switch off pump and relieve the vacuum.

Positive

A steady stream of bubbles comes from the package at one or more locations.

Negative

No bubbles are emitted from the package.

False Positive

Bubbles cling to surface of the package after package is submerged in water.

False Negative

Food particles block holes through which air might escape from defective package; or vacuum used is insufficient to force air through minute holes in package.