Modified Atmospheric Filling
The total process of product storage, bottle & cap treatment, as well as controlling the internal conditions in the aseptic zone of the filler, require special attention in order to reduce the oxygen level in the filled and sealed bottle. Stork has designed several modules and systems for this purpose: “Modified Atmospheric Filling system” (MAF).

Prevent oxygen absorption
The first step is to prevent the product to absorb oxygen in the filling bowl. This is especially important if an agitator is required. An agitator can be used in case of products containing fibres or particles. After sterilization the product tank is filled with nitrogen and during filling the required over-pressure in the filling bowl is maintained with nitrogen gas. The Stork split range pressure control system guarantees a defined over-pressure with minimal nitrogen consumption.

Formation of foam with entrapped nitrogen
During filling, depending on the product, some foam can be produced. This foam remains in the headspace of the sealed bottle. The foam is in fact entrapped air. The entrapped air will increase the final remaining oxygen level in the head space of the bottle and will therefore affect the shelf life of the product. In order to over-come this problem the second step in the process is to ad an empty bottle nitrogen flush module. Prior to filling the bottle is filled with nitrogen gas. Therefore any foam that will be produced will be entrapped nitrogen.

Purging of the bottles headspace with special nitrogen dosing nozzles 
After filling the head space of the bottles is purged with nitrogen gas. This is the third step in the Modified Atmospheric Filling process. Special dosing nozzles flush nitrogen gas into the headspace which will remove all air. A shielding above the bottle prevents the re-entering of air into the headspace after purging.

Purging of the foil caps
The fourth step is the purging of the cap. Before the aluminium foil cap is placed on the bottle the cap is purged with nitrogen gas as well. With this step we avoid air to re-enter the headspace by the application movement of the cap.
 
NVD or nitrogen around the bottle neck
After positioning the cap on the bottle neck both are transferred to the sealing station. It is important to avoid loss of nitrogen during this operation. Therefore a “blanket” of nitrogen is applied over the neck of the bottle. This is the fifth and final process step.

For the high capacity range machines (18.000 and 24.000 bph) this blanketing system can be replaced by a Nitrogen Volume Displacement (NVD) system. The NVD system maintains a nitrogen environment in a defined section of the machine. With this system any loss of nitrogen between capping and sealing is prevented, resulting in ultra low residual oxygen levels in the headspace of the filled and sealed bottle. But inevitably the nitrogen consumption will be higher compared to the blanketing system.

The combination of modules required for a specific situation totally depends upon bottle design, bottle volume, headspace and the required final oxygen level in the headspace.

Proven success - Modified Atmospheric Filling system
Stork has successfully installed the Modified Atmospheric Filling system on a number of machines with remaining oxygen residual levels in the closed bottle of 2-6%.