Beer foam is a colloidal system being built form a gas (CO2) and a liquid (beer). It is formed by CO2 release when bubbles rising in the beer are loaded with surface active substances form the beer, which form more or less stable foam when reaching the surface of the liquid according to Hedreul C. and Frens G. (2001). Foaming properties are often characterised by foaming capacity and foam stability. Foaming capacity or formability is defined as the capacity of the continuous phase to entrap air or gas and foam stability as the ability to retain the gas for a certain period of time according to Indrawati L et al (2008). During the brewing process the largest loss of head retention is during the fermentation process this is due to the loss of foam stabilizing material into the foam head such as alcohols Aldehydes, yeast crop and other negative foam factors. Other Fermentation by- products such as compounds such as Sulphur compounds, Organic acids and Diacetyl can also have a negative impact on head retention as stated by Amalia (2012). Finished beer should be handled gently and finally the maximum head retention will be observed in the beer that is cooled and poured fairly vigorously into scrupulously clean tall narrow glasses- quaternary ammonium detergents remaining on the glassware can reduce head retention as stated by Hough S. J et al (1999).
Gushing, wild over foaming beer is an undesirable quality in packaged beer. A beer is said to gush when on releasing the over pressure innumerable minute bubbles appear throughout the volume of the beer rapidly expand and displace the contents of the bottles. This can be caused by rough handling during filling and storage, Hough S. J et al (1999). Bubble nucleation is an incident that occurs in many processes in the presence of either a supersaturated or superheated liquid. This is commonly seen in the Beverage Industry. It is particularly important to understand bubble nucleation during beer dispense in the case of bubble haze production. Bubble haze is a characteristic of beer which can either be desirable or undesirable to the consumer. Bubble haze occurs when large numbers of micro bubbles are produced, which circulate within the beer rather than rise to the top. Bubble nucleation occurs in the flowing supersaturated liquid during beer dispense. The rate of nucleation during the dispense stage of beer into a glass is expected to be affected by several critical factors which include the effects of gas bubble entrainment and the presence of surfactant on the bubble surface according to Hepworth J. N. Et al (2003). In the study carried out by Hepworth J. N.. Et al (2003) it was found that the rate of bubbles produced increased with increasing flow rates and decreasing nitrogen content in the gas headspace. According to Amalia (2012) the stability of foam is improved by the use of N2 and CO2 gas for keg dispenser, using small and narrow bottles, addition of Iron Salts and the addition of gums.
A normal beer keeps its CO2 content until it is in the bottle. Sometimes the CO2 content can decreases a result of a process treatment at lower pressure or increased temperatures and must be renewed before filling. This process is known as Carbonation. The CO2 is injected in bubbles which are as small as possible so that it can dissolve in the beer. During filling it is important to avoid loss of CO2 from beer. It is essential to the quality of the beer to prevent access of Oxygen into the beer during filling which could cause oxidation as stated by Kunze W. (1999).Counter pressure fillers are always used for Beer, as it is critical that high pressures are maintained for the quality of the beer, when the bottle comes out of the filler, foam slowly rises in the bottle neck. The surrounding air has a very great tendency to dissolve in the foam and thus into the beer. The filling of beer cans is based on the same principals as bottle filling. Beer produces a much more stable foam with Nitrogen gas than with CO2 according to Kunze W. (1999). This is incorporated in a different approach in can filling. A plastic/Aluminium insert referred to as a widget is placed inside the can. They are filled with Nitrogen gas. The pressure is greater inside the widget therefore upon opening the can a pressure gradient is formed which causes the Nitrogen to escape out of the widget. The foam produced with Nitrogen consists of very fine bubbles which collapse slowly. It is also more resistant to fatty substances as stated by Kunze W. (1999).
It is seen that both bottle Filling and canning can affect the carbonation and Head retention of beer.
References:
Hedreul C. and Frens G. (2001): Foam Stability. Colloids and surfaces: A Physiochemical and Engineering Aspects. 186(1-2):73-82.
Hepworh J. N., Boyd R. W.J., Hammond M.R.J., and Varley J.(2003): Modelling the effect of liquid motion on bubble nucleation during beer dispense. Chemical Engineering Science. 58; 4071-4084.
Hough S.J., Briggs D. E., Stevens R and Young W. T. (1999): Malting and Brewing Science, Volume 2: Hopped Wort and been. 2nd Edition. Aspen Publication.
Indrawati L., Wang Z., Narsimhan G. And Gonzalez J:( 2008) Effect of processing parameters on foam formation using a continuous system with mechanical whipper. Journal of food Engineering volume.88( 1) 65-74.
Kunze W. (1999): Technology Brewing and Malting. 2nd Edition. VLB Berlin.
Scannell, A. (2012) Fermented Foods.UCD.
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