A Bottom Venting Structure for Soda Beverage Bottles Used in Carbonated Beverage Filling Machines

A Bottom Venting Structure for Carbonated Beverage Bottles Used in Carbonated Beverage Filling Machines (1)

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Carbonated beverage bottles need a specialized bottom venting structure to release excess air during the filling process. This allows the bottles to be filled efficiently on high-speed carbonated beverage filling machines. Over the years, different bottom venting structures have been developed and patented to improve bottle quality, filling speeds, and reduce manufacturing costs. This article explores the evolution of bottom venting structures for carbonated beverage bottles and how the latest designs provide key benefits for beverage producers.

A Bottom Venting Structure for Carbonated Beverage Bottles Used in Carbonated Beverage Filling Machines (1)
A Bottom Venting Structure for Carbonated Beverage Bottles Used in Carbonated Beverage Filling Machines (1)

The Need for Effective Venting in Carbonated Plastic Bottles

Carbonated beverages like soda, beer, sparkling water and mineral water contain dissolved carbon dioxide gas. This pressurized gas helps create the characteristic bubbles and fizz. When filling carbonated beverages into bottles on high-speed filling lines, the bottles need to vent this excess gas to avoid foaming and overflow.

The first glass bottles used for carbonated drinks in the late 1890s and early 20th century had small openings around the crown edge to let gas escape. But as filling technology advanced, bottle shapes evolved to allow faster filling speeds. This created a need for a separate bottom venting structure.

Modern soft drink beverage bottles are filled at speeds over 1,000 bottles per minute on rotary filling machines. At these speeds, the bottle needs an effective venting solution during the filling process. This is where the specialized bottom vent structure comes in.

Early Bottom Venting Solutions for Liquid Packaging

The first bottom venting solutions involved placing small holes in the bottom center of the bottle. This allowed gas to escape through the holes while filling. Early versions had around 10 vent holes of 1 mm diameter.

While simple, this approach faced some downsides:

  • The small vent holes restricted gas flow, slowing down filling speeds.
  • Bottles needed high filling pressures around 30 bar to fully fill before capping. High pressure increased energy use.
  • Lower filling pressures caused bottle bottoms to be unsaturated, affecting stability.

Table 1: Bottom Vent Structure Specifications

Locating bossMounted at the center bottom of the soft drink beverage bottle
Claws5 equally spaced claws connected to the outer edge of the locating boss
Claw groovesGrooves between adjacent claws
First vent holes≥3 vent holes on each claw, diameter 2mm
Second vent holes≥6 vent holes on each claw, diameter 1.5mm

Despite the drawbacks, these early venting solutions were simple and low cost. They met basic venting needs before the introduction of more advanced designs.

The Move to Larger Vent Holes

By the late 1950s, new bottom venting structures emerged aiming to improve venting performance. The key change was increasing the size and number of vent holes.

Instead of ~10 x 1mm holes, new structures incorporated:

  • 3 or more 2mm diameter holes
  • 6 or more 1.5mm diameter holes

With around double the venting area, these new “multi-hole” designs significantly increased venting capacity. This allowed:

  • Faster filling speeds and throughput
  • Lower filling pressures around 26 bar or less
  • More uniform bottle filling and bottom saturation

The 2mm holes rapidly expelled large volumes of gas during filling. The smaller 1.5mm holes ensured thorough venting after the initial surge.

This multi-hole approach gained widespread adoption and still remains a common solution today. While simple, it marked a major improvement in filling performance.

Integrating Venting into the Bottle Base

Another advancement was moulding the vent holes directly into the bottle base. Earlier methods added vent holes in a separate step after moulding the bottle.

Integrating vent holes into the bottle mould allowed:

  • Vent holes to be incorporated into the base design
  • More flexibility in vent hole shape, size, and location
  • Eliminated a production step lowering costs

This allowed venting performance to be optimized through the base geometry itself. For example, angling vent holes to follow the base curvature improved venting. Different hole shapes like ovals or slots also improved gas flow.

Advanced Base Geometries

A Bottom Venting Structure for Carbonated Beverage Bottles Used in Carbonated Beverage Filling Machines (2)
A Bottom Venting Structure for Carbonated Beverage Bottles Used in Carbonated Beverage Filling Machines (2)

With in-mold vent holes, bottle base shapes could be designed to maximize venting while preserving strength and stability. This led to advanced base geometries in the 1960s and 70s.

Some of the design innovations included:

Concave Base Structures

  • Creating a concave indentation in the base provided more surface area. This let gas escape through more vent holes.

Radial Base Ribs

  • Radial ribs running along the base curve added rigidity. This allowed minimizing base thickness to improve venting.

Stepped Base Structures

  • Stepped base profiles with thinner center sections reduced material above vent holes. This decreased venting obstruction further.

These techniques enabled bottles to vent at lower pressures. Thinner bases also used less material, reducing costs. The advanced designs improved filling throughput and efficiency.

Modern Venting Trends for Container

While the fundamentals remain similar, certain trends are shaping modern bottom venting structures:

Larger Vent Holes

  • New PET bottle materials allow vent holes up to 5mm diameter while preserving base strength. Larger holes significantly boost venting rates.


  • RFID tags are being incorporated into bottle bases. Vent holes help hide and protect the RFID tags during filling.

Filling Valve Integration

  • Bottom contours are being optimized to pair with filling valve geometry. This improves filling accuracy and clean venting cut-off.


  • Using as little material as possible through advanced base shaping reduces container weight and material usage.


  • Priority is placed on 100% recyclable materials and clear separation between materials like vent tubes. This improves recyclability.

The Benefits of Effective Bottom Venting Structures

Advanced bottom venting structures provide significant benefits for both soft drink producers as well as consumers:

Faster, More Efficient Filling

  • Increased venting capacity allows higher filling speeds and throughput with less bottlenecks.

Lower Filling Pressures

  • More effective venting means less pressure is required during filling. This saves energy and reduces carbon emissions.

Improved Container Quality

  • Thorough venting gives more uniform fills and fuller bottom shapes. This results in better stability, strength, and aesthetics.

Lower Production Costs

  • Integrated vent hole formation and lightweight base designs reduce material usage and per bottle costs.

Greater Consumer Appeal

  • Clean filling with minimal foaming provides a quality appearance to consumers. Stable bases prevent tipping or rocking.

With continued innovation, venting technology will keep pace with the ever-increasing demands of high-speed beverage filling.

Table 2: Benefits of New Bottom Vent Structure

Lower blow molding pressureCan be lowered to ≤26 bar
Energy savingsReduces energy consumption and production costs
Improved bottle stabilityAllows the bottom to be stretched fully for better saturation and stability
Improved burst resistanceDue to improved bottom saturation

Frequently Asked Questions About Bottom Vent Structures

Bottom vent structures play an important role in soda beverage filling, but the details can sometimes be confusing. Here are answers to some frequently asked questions:

Why are separate bottom vents needed? Can’t the gas escape through the bottle opening?

At modern filling speeds of over 1,000 containers per minute, the bottle opening does not provide nearly enough venting capacity. The pressurized gas buildup would cause foaming over. Bottom vents provide the needed gas release.

How many vent holes are typically used on a bottle?

Most current designs use between 9 to 12 total vent holes, with larger primary holes supplemented by additional smaller vent holes. However, some new designs are incorporating up to 20 holes.

Are vent holes found on plastic bottles too?

Yes, PET plastic bottles require venting just like glass. The vent holes are molded right into the plastic base during fabrication.

Does beer bottle venting differ from soda bottles?

The fundamentals are the same, but beer bottles sometimes use more vent holes due to higher carbonation levels. They may also utilize ribs or recesses to strengthen the base.

How does vent hole sizing affect performance?

Larger vent sizes generally increase flow rates allowing faster filling. But they can impede draining and drying during the filling process if overly large. Optimizing size based on the filling system is key.

Where should the vent holes be located?

Centering the vents on the push-up helps promote even draining after filling. Keeping away from the outer base helps avoid the filling jets. An evenly spaced circular pattern works well.

Do vent holes affect bottle stability or strength?

With proper design consideration, vent holes should not compromise bottle stability or ability to withstand top load. Critical areas are reinforced, and drop testing validates strength.


Effective bottom venting is critical for the high-speed filling of CSD beverages. As filling technology has evolved, so have the bottle bases designed to meet these needs. Multi-hole venting, integrated molding, and advanced base geometries have improved filling performance and efficiency. With increasing emphasis on lightweighting, recyclability, and compatibility with carbonated beverage filling machinery, bottom vent structures will continue advancing. Proper venting ensures bottle quality while allowing producers to meet demand. The next time you open a CSD beverage, take a moment to appreciate the ingenuity in its humble base.

For companies looking to optimize productivity and costs, our carbonated beverage filling machines offer the latest filling technology paired with expertise in container venting solutions. Contact us today to discuss how our iBottling equipment can meet your production goals.

Reference Source

Picture of John Lau.
John Lau.

John Lau, oversea project manager, an engineering graduate with expertise in optimizing beverage production equipment during his university studies, is now at the helm of global projects in the industry. Committed to educating clients on the benefits of customized equipment solutions that notably boost operational efficiency, Lau views this specialization in tailoring bottling machines as a key facet of his professional commitment.

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