THE MECHANISM OF GUSHING-A REVIEW

The Gushing Experience—A Quick Overview

Beer lovers all over the world like to get their drink with a certain volume of stabile foam, which mainly depends on the beer style. However, sometimes this foam comes in form of a sudden, eruptive, and uncontrolled over-foaming (gushing) of beer. Gushing occurs after the bottle has been opened, without previously being treated inappropriately (exposure to high temperatures, shaking, or any other kind of agitation). According to recent scientific and professional literature, gushing may be induced by many factors, but fungal proteins are directly connected to this phenomenon. Gushing caused by fungal proteins—hydrophobins—is called primary gushing, and depends solely on raw material quality. Other reasons for extensive foaming after the bottle has been opened can be of chemical or technological nature in the course of the brewing process. This is called secondary gushing, which can be influenced and reduced by applying good manufacturing practice protocols.

Dynamic fluid-film interferometry as a predictor of bulk foam properties

Understanding and enabling the control of the properties of foams is important for a variety of commercial processes and consumer products. In these systems, the role of surface active compounds has been the subject of many investigations using a wide range of techniques. The study of their influence on simplified geometries such as two bubbles in a liquid or a thin film of solution (such as in the well-known Scheludko cell), has yielded important fundamental understanding. Similarly, in this work an interferometric technique is used to study the dynamic evolution of the film formed by a single bubble being pressed against a planar air-liquid interface. Here interferometry is used to dynamically measure the total volume of liquid contained within the thin-film region between the bubble and the planar interface. Three different small-molecule, surfactant solutions were investigated and the data obtained via interferometry were compared to measurements of the density of bulk foams of the same solutions. The density measurements were collected with a simple, but novel technique using a conical-shaped bubbling apparatus. The results reveal a strong correlation between the measurements on single bubbles and complete foams. This suggests that further investigations using interferometric techniques can be instrumental to building a more detailed mechanistic understanding of how different surface-active compounds influence foam properties. The results also reveal that the commonly used assumption that surfactant-laden interfaces may be modeled as immobile, is too simplistic to accurately model interfaces with small-molecule surfactants.

Recent Advances in Fungal Hydrophobin Towards Using in Industry

Fungal hydrophobin is a family of low molecular weight proteins consisting of four disulfide bridges and an extraordinary hydrophobic patch. The hydrophobic patch of hydrophobins and the molecules of gaseous CO2 may interact together and form the stable CO2-nanobubbles covered by an elastic membrane in carbonated beverages. The nanobubbles provide the required energy to provoke primary gushing. Due to the hydrophobicity of hydrophobin, this protein is used as a biosurfactant, foaming agent or encapsulating agent in food products and medicine formulations. Increasing demands for using of hydrophobins led to a challenge regarding production and purification of this product. However, the main issue to use hydrophobin in the industry is the regulatory affairs: yet there is no approved legislation for using hydrophobin in food and beverages. To comply with the legislation, establishing a consistent method for obtaining pure hydrophobins is necessary. Currently, few research teams in Europe are focusing on different aspects of hydrophobins. In this paper, an up-to-date collection of highlights from those special groups about the bio-chemical and physicochemical characteristics of hydrophobins have been studied. The recent advances of those groups concerning the production and purification, positive applications and negative function of hydrophobin are also summarised.

Investigation of overfoaming activities and gushing mechanisms of individual beer ingredients as model substances in bottled carbonated water

BACKGROUND

Researchers in several disciplines are interested in understanding the spontaneous and eruptive overfoaming (gushing) of carbonated beverages, as it is an essential problem of both the brewing and beverage industries. In order to understand the mechanism(s) taking place in gushing beer, several beer ingredients have been investigated as model substances in a much simpler matrix of carbonated water. For this purpose, sinapic acid, vanillic acid, ferulic acid, cinnamic acid and palmitic acid have been chosen as model beer ingredients.

RESULTS

Gushing formation of the investigated beer ingredients depends on the degree of stabilized solvated molecular carbon dioxide in water. For this purpose, functional groups capable of forming hydrogen bonds with electronegative oxygen atoms of carbon dioxide are needed. However, the solubility of the substances plays an important role in the abundance of these functional groups in undissociated form to interact with molecular carbon dioxide.

CONCLUSION

The reported data provide valuable insights into the gushing problem and help to understand its formation pathways. Each gushing-positive substance has an individual mechanism related to its structural conformation and solubility level. Therefore possible gushing mechanisms have been proposed with respect to the structural changes in model substances to clarify the differences in observed overfoaming and gushing stability levels.