The Beer Brewer

See our previous article for part 2

Beer haze may also be addressed during maturation (pre-filtration) using precipitants. Proteolytic enzymes such as papain can be used to remove (hydrolyse) haze proteins, although the enzyme can also have a negative impact upon finished product, as it is relatively non-specific and often hydrolyses foam active proteins to destroying a beers head. However, research conducted by Eden et al (2005), using a proline specific protease enzyme (from the microorganism Aspergillus niger), resulted in the prevention of chill haze in beers without having a negative impact on the foam active proteins, as they are very low in proline. This enzyme may prove to be a viable option for brewers in the future.

Tannic acid (a polyphenol) interacts with HA proteins to form insoluble precipitates in the beer. These precipitates are frequently voluminous, thus beer losses via this mechanism can be large.

Fining with agents such as gelatine can also remove HA protein.

Microbrewers often rely on the more traditional method of extended cold storage and filtration to precipitate and remove HA material, which can result in a less stable product.

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Beer Clarity part 1

Beer is subject to colloidal instability during storage. Chill filtered beer initially remains haze free, however, as the product ages it passes through a series of metastable colloidal states, whereby chill hazes and eventually insoluble (permanent) hazes form, primarily as a result of protein-polyphenol interactions within the product. Haze reactions are significantly accelerated with increasing temperature, due to an increase in the rate of reactions (Kunze, 1999).

Proteins and polyphenols are natural components of beer which are extracted from malt and hops. Haze active (HA) proteins contain high percentages of the amino acid proline and are thought to be the degradative products (as a result of the malting and brewing process) of barley hordein. Globulin and albumin proteins are also regarded as haze active, as they associate with polyphenols in the beer to form hazes upon removal of the proline containing proteins.

The polyphenols primarily involved in haze formation are barley flavanoids such as catechin, or polymers of the latter, proanthocyanidins.

The mechanism of haze formation is the following: Haze active proteins contain a number of active sites, thought to be the proline residues, which have a specific affinity for polyphenols. If polyphenols have two binding ends, they are capable of linking protein molecules together, forming colloidal particles, which create haze. Smaller colloidal particles initially form in beer, as there are insufficient amounts of polyphenols to link any more than two protein molecules together, hence light hazes form.  Larger particles and increased haze can form when polyphenol levels approach those of the protein (due to oxidative reactions during storage ), as polyphenol linking of the proteins can form large networks.

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Beer colour is the result of the concentration of highly coloured melanoidin and caramel compounds in solution. These compounds are primarily formed via Maillard type reactions between aldose type sugars and amino acid groups, which occur primarily during extreme heating stages of the malting and wort production phases of the brewing process i.e. malt kilning and wort boiling. Melanoidin compounds are extracted from the malt during mashing and form during boiling. Therefore, the desired colour of a beer may be achieved by employing malts of particular colour and boil times of appropriate duration.

However, as packaged beer may contain amino acids and reducing sugars in solution Maillard reactions may still occur in the product, particularly if the beer is subjected to storage under conditions that favour this reaction, namely elevated temperatures, long time periods or a combination of both. Studies have attributed colour increases during ageing to such Maillard reactions.

The polyphenols in beer are also subject to degradation via oxidation reactions catalysed by light, oxygen, oxidising agents, and heavy metals, to form darker coloured quinonoid bases that result in an increase in beer colour.

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Brettanomyces species, particularly B. limbicus and B. bruxellensis also become active during this period, from approximately 8 months onward (figure to follow). These yeasts are capable of fermenting dextrins (found in relatively high levels in lambic wort), maltotriose and maltotetraose, producing small amounts of acetic acid and ethanol. However, it is the production of unique flavour and aroma compounds that characterises the activity of Brettanomyces. Brettanomyces exhibits a high esterase activity, primarily resulting in the synthesis of large amounts of ethyl acetate and ethyl lactate. This esterase  also cleaves iso- amyl acetate esters, thus accounting for its low concentration in lambic beer.

Tetrahydropyridines are also produced from ethanol and the amino acid lysine, which impart a ‘mousy’ or ‘horsy’ aroma to the beer. Volatile phenolics, with medicinal, ‘barnyard’ or ‘animal’ type odours are also from from 4-ethyl phenol and 4-ethyl guaiacol compounds.

Brettanomyces activity also leads to a significant increase in caprylic (C8) and caprix (C10) acids (small amounts are formed during earlier Saccharomyces acitivity) along with their associated esters, ethyl caprylate and ethyl caprate. These compounds produce a characteristic ‘goaty’ aroma/flavour to the final product. Capric and caprylic acids are short chain fatty acids and are thought to be by-products of yeast metabolism, produced during lipid synthesis by a yeast cell and released into the medium via leakage through membranes damaged by ethanol, or as a consequence of an autolytic mechanism. Higher temperatures, aeration and agitation during fermentation reduce the amounts of fatty acids in beer. Reduced aeration/agitation produced higher concentrations. The combined threshold for C6-C12 acids is 10ppm, beyond which ‘goaty’ aromas arise. C8 acid levels in gueuze as 12.4 - 21.85 ppm and C10 acids as 2.3 - 3.9p ppm.

Brettanomyces is active until the end of the fermnetaion period. Acetic acid bacteria of the genus Acetomonas and a number of oxidative yeasts (Pichia, ) are also found during lambic fermentations, however their influence is often minimal.

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As the Saccaromyces species decline once the primary fermentation is completed (2 months), the secondary or lambification (acidifcation) phase, initially involving the hop tolerant Pediococcus damnosus, takes place. P. damnosus is the primary producer of lactic acid in lambic beer, as it is a homofermentative organism producing only lactic acid from the metabolism of glucose, via the EMP pathway. As lactic acid is a key component in lambic flavour, its production is considered here: Glucose undergoes enzymatic cleavage and substrate level phosphorlyation, producing glcyeraldehyde 3 - phosphate, a proportion of which is converted to pyruvate. Lactic acid is produced from pyruvate by the the enzyme lactate dehydrogenase. No gas is evolved. The taste threshold for lactic acid is 400ppm. Final concentrations are indicated as between 492 - 3677ppm.

Fermentation at temperatures above 20oC are required for P. damnosus growth, therefore increasing temperatures beyond this level will stimulate lactic acid production as cell numbers increase. P. damnosus is a also a facultative anaerobe, thus the exclusion of air during P. damnosus activity will presumably facilitate the further production of lactic acid.

P. damnosus is also a producer of diacetyl, prodcuing up to 200ppb during this period. Acetoin is also produced as a consequence . The production of large amounts of lactic acid result in a drop in beer pH from 4 to 3, with a gradual lowering of residual extract.

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An Introduction to Lambic Beers

The Belgian lambics are unique beers, traditionally produced in the Payottenland region of Belgium, via a process of spontaneous fermentation, as opposed to the controlled inoculation and fermentation procedures used in the production of other beer styles. This type of traditional, spontaneous fermentation is employed in combination with differing raw materials and production processes, to produce beers with unique flavour and aroma profiles, which have not been reproducible via other methods. Spontaneous fermentation is facilitated by overnight exposure of the cooling (un-inoculated) wort to the predominant air borne microflora of the brewery, which rapidly establish themselves within the wort.

There are two major phases of fermentation underaken in lambic beer, both involving the activities of bacteria and yeast; a primary phase, lasting for 3-4 months, characterized by the production of high amounts of ethanol; and a second, slower period of “lambification” or acidification, lasting for 12-24 months. A subsequent third (bottle) fermentation phase may be used to produce a gueuze style lambic.

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Just a quick message to say that we’ll be publishing some great articles about beer and beverages shortly.

Thanks and keep an eye on us - we’ve got great plans afoot!

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