Isobaric filling, also known as counter pressure bottle filling, is a specialized technique used in the beverage industry to bottle carbonated drinks without losing their fizz. This method is essential for maintaining the quality and consistency of products like beer, sparkling wine, and soda.  

Meaning and Functioning of Isobaric Filling

At its core, isobaric filling focuses on maintaining equal pressure between the beverage tank and the bottle throughout the filling process. This is achieved by introducing CO2 gas into the bottle before filling, creating a counter pressure that matches the pressure in the tank. This prevents the dissolved CO2 in the beverage from escaping as foam, preserving the carbonation.  

Isobaric Filling Process

During isobaric filling, the bottle is first sealed using the gasket of the filling valve.

Depending on the type of product to be bottled, a vacuum is initially created inside the bottle by sucking the air into it. This air contains mainly oxygen and nitrogen, but it is necessary to remove the oxygen to ensure a significantly longer shelf life (the TOP, which measures the oxygen in a beer bottle, represents the total oxygen pick-up rate and is usually measured in parts per billion, with a desirable range of 40-100 ppb). This is known as pre-evacuation of the air, often repeated twice to eliminate the percentage of residual oxygen before the actual filling.

At this stage, the bottle is saturated mainly with CO2 under pressure, approximately 2.2 to 3.0 bar.

The valve at the top of the filling tank is opened to allow the oxygen to escape.

The filling valve is then opened, allowing beer to flow into the container. The pressure gradually drops through the vent valve, allowing CO2 to escape and beer to fill the space previously occupied by the gas. During this process, continuous pressurization minimizes foaming. Once the bottle is full, the liquid supply valve is sealed. Any residual pressure is released through the vent valve and the bottle is then capped.

Once sealed, bottles are typically washed on the outside with a gentle stream of water to remove any sugary or sticky residue that may have settled on the outside of the bottle.

When to Use Isobaric filling

Isobaric filling is primarily used for:

• Carbonated beverages: Beer, sparkling wine, cider, soda, and any drink where carbonation is key.  
• Delicate beverages: Wines with low residual sugar or high acidity, where excessive foaming can be detrimental.
• Craft producers: Smaller breweries and wineries that prioritize quality and flavor preservation.

Beer Isobaric filling

In beer production, isobaric filling is crucial for maintaining the characteristic head and mouthfeel. It helps to:

• Preserve hop aromas: Volatile compounds responsible for hoppy flavors are retained.
• Prevent oxidation: CO2 acts as a barrier against oxygen, which can cause beer to stale.
• Ensure consistent carbonation: Each bottle has the same level of fizziness.

Sparkling Wine Isobaric Filling

For sparkling wines, isobaric filling ensures the delicate bubbles and complex aromas remain intact. It also helps to:  

• Minimize oxygen pickup: Oxidation can lead to loss of fruitiness and freshness.
• Reduce foaming: Excess foam can lead to product loss and inconsistency.
• Preserve acidity: Maintaining proper acidity is crucial for sparkling wine’s flavor profile.

Wine Isobaric filling

While not as common for still wines, isobaric filling can be beneficial for certain styles, particularly those with low residual sugar. It can help to:

• Prevent oxidation: Especially important for white and rosé wines.
• Preserve volatile aromas: Some aromatic compounds are sensitive to pressure changes.
• Achieve consistent fill levels: Isobaric filling can lead to more accurate fills.

Why Is Foam Produced Without Isobaric filling?

To answer this question it is first necessary to explain what it is and why the foam is produced: any alteration of the pressure during the bottling process of a product gased in a bottle or in another container will inevitably cause the expansion of the content and training of foam, or gas bubbles in the product. The intensity of this phenomenon is directly proportional to its temperature: the more high, the more marked the foam effect.

The propensity for foam formation varies between the different products. In general, the quantity of proteins and sugars present in a drink affects foam production. For example, the beer is more susceptible than the carbonated water and, inside the beers themselves, some may be more sensitive than others, depending on the level of protein present in the composition.

How Does Isobaric filling Solve the Problem?

Using isobaric filling, foam formation can be almost completely avoided during the filling process. Eliminating or reducing foam is most effective through controlling the temperature of the product. For example, the ideal temperature for filling most beers is 2°C from the storage tanks, increasing to 3-4°C during bottling.

Using this machine also allows for stabilizing fluctuations in pressure variations between the storage tank, the carbonator (if used to carbonate the product) and the filling machine.

The Advantages of Isobaric filling

• Consistent carbonation: Ensures each bottle has the intended level of fizziness.
• Flavor preservation: Protects delicate aromas and flavors from oxidation and loss.
• Reduced product waste: Minimizes foam and overflow, saving valuable beverage.  
• Improved quality: Leads to a more consistent and enjoyable drinking experience.

Conclusion

Isobaric filling is a valuable technique for beverage producers looking to bottle their products with precision, efficiency, and quality in mind. By eliminating foaming and preserving the beverage’s characteristics, isobaric filling ensures that the final product is as close as possible to the original in the filling tank. Whether it’s beer, sparkling wine, or soft drinks, isobaric filling offers a reliable solution for maintaining carbonation, flavor, and overall product quality.