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The chemical compounds in beer give it a distinctive taste, smell and appearance. The majority of compounds in beer come from the metabolic activities of plants and yeast and so are covered by the fields of biochemistry and organic chemistry. The main exception is that beer contains over 90% water and the mineral ions in the water (hardness) can have a significant effect upon the taste.
Many patents for various types of beer foam stabilizers have been filed by breweries and the agro-chemical industry in the last decades. Cobalt salts added at low concentration (1 – 2 ppm) were popular in the sixties, but raised the question of Cobalt poisoning in case of undetected accidental overdosage during beer production. As an alternative, organic foam stabilizers are produced by hydrolysis of recovered by-products of beer manufacture, such as spent grains or hops residues.
Amongst the large spectrum of purified, or modified, natural available on the market, soluble carboxymethyl hydroxyethyl cellulose, propylene glycol alginate (PGA, food additive with E number E405), and gellan gum have also been investigated as foam stabilizer.
Cobalt is a transition metal whose are able to interact with , or (–OH, –COOH, –NH2), attached to organic molecules naturally present in the beer, making macromolecule coordination complexes stabilizing the beer foam. Cobalt could behave as an inter- or intra-molecular bridge between different polysaccharide molecules (changing their shape or size), or cause some conformational changes of different types of molecules present in solution, affecting their absolute configuration and thus the foam molecular structure and its behavior.
Thorne and Helm (1957) also formulated the hypothesis that cobalt, by being complexed with certain nitrogenous constituents of the beer (e.g., from malt ), might produce Surfactant inactivating the gaseous nuclei responsible for Foam and gushing.
Gushing is a specific problem also studied into more details by Rudin and Hudson (1958). These authors discovered that gushing is also promoted by other transition metal such as these of nickel and iron, but not by cobalt ions. Isohumulone (an iso-alpha acid responsible for the Taste of hops) and its combinations with Ni, or Fe, also favor gushing, while pure Co ions or their combination with isohumulone do not exhibit gushing and overfoaming. This explains why cobalt salts were specifically selected at a concentration of 1 – 2 mg/L as anti-gushing agent for beer. Rudin and Hudson (1958) and other authors also found that Co, Ni and Fe ions preferentially concentrate in the foam itself.
In the sixties, after approval by the US FDA, cobalt sulfate was commonly used at low concentration in the USA as an additive to stabilize beer foam and to prevent gushing after beer is exposed to vibrations during its transport or handling.
Although cobalt is an essential micronutrient needed for vitamin B12 synthesis, excess levels of cobalt in the body can lead to cobalt poisoning and must be avoided. It triggered the development of qualitative and quantitative analysis methods to accurately assay cobalt in beer in order to prevent accidental overdosage and cobalt poisoning.
Too high levels of cobalt are known to be responsible for the beer drinker's cardiomyopathy. The first issues mentioned in the literature were reported in Canada in the middle of the sixties after an accidental overdosage in the Dow Breweries in Quebec City.
In August 1965, a person presented to a hospital in Quebec City with symptoms suggestive of alcoholic cardiomyopathy. Over the next eight months, fifty more cases with similar findings appeared in the same area with twenty of these being fatal. It was noted that all were heavy drinkers who mostly drank beer and preferred the Dow Breweries; thirty out of those drank more than 6 litres (12 pints) of beer per day. Epidemiology found that the Dow Breweries had been adding cobalt sulfate to the beer for foam stability since July 1965 and that the concentration added in the Quebec city brewery was ten times that of the same beer brewed in Montreal where there were no reported cases.
Beer is unique when compared to other alcoholic beverages because it is unstable in the final package. There are many variables and chemical compounds that affect the flavor of beer during the production steps, but also during the storage of beer. Beer will develop an off-flavor during storage because of many factors, including sunlight and the amount of oxygen in the headspace of the bottle. Other than changes in taste, beer can also develop visual changes. Beer can become hazy during storage. This is called colloidal stability (haze formation) and is typically caused by the raw materials used during the brewing process. The primary reaction that causes beer haze is the polymerization of polyphenols and binding with specific proteins. This type of haze can be seen when beer is cooled below 0 degrees Celsius. When the beer is raised to room temperature, the haze dissolves. But if a beer is stored at room temperature for too long (about 6 months) a permanent haze will form. A study done by Heuberger et al. (2012) concludes that storage temperature of beers affects the flavor stability. They found that the metabolite profile of room temperature and cold temperature stored beer differed significantly from fresh beer. They also have evidence to support significant beer oxidation after weeks of storage, which also has an effect on the flavor of beer.
The off-flavour in beer, such as a cardboard or green apple taste, is often associated with the appearance of staling aldehydes. The Strecker aldehydes responsible for the flavor change are formed during storage of the beers. Philip Wietstock et al. performed experiments to test what causes the formation of Strecker aldehydes during storage. They found that only amino acid concentration (leucine (Leu), isoleucine (Ile), and phenylalanine (Phe), specifically) and dissolved oxygen concentration caused Strecker aldehyde formation. They also tested carbohydrate and Fe2+ additions. A linear relationship was found between Strecker aldehydes formed and total packaged oxygen. This is important for brewers to know so that they can control the taste of their beer. Wietstock concludes that capping beers with oxygen barrier crown corks will diminish Strecker aldehyde formation.
In another study done by Vanderhaegen et al. (2003), different aging conditions were tested on a bottled beer after 6 months. They found a decrease in volatile was responsible for a reduced fruity flavor. They also found an increase in many other compounds including carbonyl compounds, ethyl esters, Maillard compounds, dioxolanes, and furane ethers. The carbonyl compounds, as stated previously in the Wietstock experiments, will create Strecker aldehydes, which tend to cause a green apple flavor. are known to cause fruity flavors such as pears, roses, and bananas. Maillard compounds will cause a toasty, malty flavor.
A study done by Charles Bamforth and Roy Parsons (1985) also confirms that beer staling flavors are caused by various carbonyl compounds. They used thiobarbituric acid (TBA) to estimate the staling substances after using an accelerated aging technique. They found that beer staling is reduced by scavengers of the hydroxyl radical (•OH), such as mannitol and ascorbic acid. They also tested the hypothesis that soybean extracts included in the fermenting wort enhance the shelf life of beer flavor.
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