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Guinness Beer Bubbles May Lead To Improvements In Wastewater Treatment And Quality Control For Fermented Foods

World’s first scientific research on the mechanism of the iconic beer’s unique bubble flow

  • Research and Technology

July 7, 2021

Kirin Holdings Company, Limited

TOKYO, Monday September 28, 2020 – Kirin Holdings Institute for Future Beverages conducted joint research with a research group led by Tomoaki Watamura and Kazuyasu Sugiyama from the Fluids Engineering Research Group of the Graduate School of Engineering Science at Osaka University. Through this joint research, the first-ever mathematical expression for the mechanism of bubble cascade formation in a glass of Guinness beer was discovered, and the results of the research were published in the United States’ Physical Review E scientific journal on June 8, 2021.

During joint research conducted with the Graduate School of Engineering Science at Osaka University in 2019, it was found that the bubbles in Guinness Draught form a pattern as bands of liquid roll down the inclined surface of the glass that is similar to the “rolling wave*1 pattern” which appears when rainwater rolls down an incline.
*1 Wave that appears on the surface of a liquid flowing down an incline. Typical examples include the waves visible on rainwater flowing down a solid surface or a window pane.

Understanding Liquid Flow can Help Societal Issues

Understanding and predicting the conditions of formation is expected to lead to improvements in wastewater treatment and quality control for fermented foods when applying these conditions. In fact, mathematical models like the one in this study describing the flow of liquids have been applied to other phenomena such as the spread of infectious diseases and traffic congestion.

In this case, carbonated water, cola and other non-stout beers do not exhibit similar patterns – they flow upwards - and it was previously impossible to explain why these bubbles and the bubbles in Guinness beer move in different ways. Also, in the experiment-oriented research conducted to date, because the test subject is a liquid, it was not possible to control the volume or size of the bubbles. However this study used a supercomputer to conduct a simulation, and through the successful discovery of a mathematical model for the formation of the bubble cascade, it was revealed that the pattern forms through the collective flow of dense bubbles under certain conditions.

Furthermore, the research found that the pattern can appear if relatively dense conditions are created when pouring carbonated water or cola into an extremely large container such as a 200-liter drum (as opposed to a small glass).

Background of the research

The bubbles in the iconic Guinness beer are made of nitrogen gas. They are only about 1/10 (50μm in diameter) the size of the bubbles in carbonated beverages and rise slowly. Because a large volume of bubbles remain in the beer for a long period of time, the beer has a creamy flavor, and it also leads to a unique pattern (Figure 1) created from collective bubble flows. However, a scientific explanation governing the formation of this bubble pattern remained elusive, and it was viewed to be a peculiar phenomenon.

Details of the research

This discovery governing the existence of a bubble cascade and movement of the bubbles was deemed to be impossible because the test subject is a beverage and the experiments could only be conducted under limited conditions. The current research group used a supercomputer to conduct simulations in which the Guinness beer bubble cascade was recreated under approximately 400 conditions. By creating a mathematical model*2 from the equations for bubble and liquid movement, the research group successfully identified the scaling law*3 of the flow.
*2 Use of mathematical equations to describe and analyze natural phenomena.
*3 Laws that describe the conversionary relationship between two physical quantities. These laws are used when discussing physical quantities that are in a proportional relationship or follow “power law” and “exponential law”.

Research results

This research discovered that the bubble cascade phenomenon is determined by an indicator representing stability or instability (Froude number*4) and indicator representing the density or sparsity of the bubbles (resolution of the concentration interface*5). Also, through the creation of a mathematical model, it is now possible to predict the occurrence of this phenomenon based on the shape of the cup.
*4 Dimensionless number that represents the ratio between inertial force and gravitational force in liquids. It is mainly used for indicating the status of wave formation on the surface of water. Small Froude numbers indicate situations in which it is difficult for waves to form, and large Froude numbers indicate situations in which it is easy for waves to form.
*5 Dimensionless number that represents that ratio between average distance between bubbles and liquid film thickness. As the bubbles rise, a liquid film with no bubbles forms at the inclined inner surface, and this figure indicates the level of bubble density by comparing the average distance between bubbles with this liquid film.

Supplementary information regarding the relevant research papers

2021

Title: “Bubble cascade may form not only in stout beers”
Authors: Tomoaki Watamura, Kazuyasu Sugiyama,
Yuko Yotsumoto, Mihoko Suzuki, and Hideyuki Wakabayashi
Published: June 8, 2021
Journal Physical Review E (United States)

2019

Title: “Bubble cascade in Guinness beer is caused by gravity current instability”
Authors: Tomoaki Watamura, Fumiya Iwatsubo, Kazuyasu Sugiyama,
Kenichiro Yamamoto, Yuko Yotsumoto, Takashi Shiono
Published: April 5, 2019
Journal Scientific Reports (England)

About Kirin Holdings

Kirin Holdings Company, Limited is an international company that operates in the Food & Beverages domain (Food & Beverages businesses), Pharmaceuticals domain (Pharmaceuticals businesses), and Health Science domain (Health Science business), both in Japan and across the globe.

Kirin Holdings can trace its roots to Japan Brewery which was established in 1885. Japan Brewery became Kirin Brewery in 1907. Since then, the company expanded its business with fermentation and biotechnology as its core technologies, and entered the pharmaceutical business in the 1980s, all of which continue to be global growth centers. In 2007, Kirin Holdings was established as a pure holding company and is currently focusing on boosting its Health Science domain.

Under the Kirin Group Vision 2027 (KV 2027), a long-term management plan launched in 2019, the Kirin Group aims to become “A global leader in CSV, creating value across our world of Food & Beverages to Pharmaceuticals.” Going forward, the Kirin Group will continue to leverage its strengths to create both social and economic value through its businesses, with the aim of achieving sustainable growth in corporate value.

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