Colour of beers

A hundred thousand years ago, Man had begun to prepare food with the aid of fire, and started chemistry while cooking. With help from the Maillard reaction, the taste of his food became more sophisticated and pleasant. The typical smell of warm, crusty bread, the marvellous taste of a roast, the fine odour of roasted coffee, the spicy aroma and the colour of beer, result all from this little-known named reaction. Precise analysis of food ingredients and the development of highly specialised processing technologies allow for the industrial-scale preparation of tasty, appealing and readily available meals and snacks, which are... 

Caramel may be used either in the copper or in primings to make minor adjustments to the colour of beer but the fundamental colour of the beer will be determined by the choice of malt grist and the grade of adjuncts added to the copper. 

The colour of beer is largely determined by the melanoidins and caramel present in the malt and adjuncts used but further caramelization occurs during wort boiling. Minor adjustments of the colour of beer can be made by the addition of caramel either to the copper or with primings. The chemistry of melanoidin and caramel formation is discussed in Chapter 14. 

Application of Beer s Law. Consider the case of two solutions of a coloured substance with concentrations c, and c2. These are placed in an instrument in which the thickness of the layers can be altered and measured easily, and which also allows a comparison of the transmitted light (e.g. a Duboscq colorimeter, Section 17.5). When the two layers have the same colour intensity ... 

A colorimeter can, therefore, be employed in a dual capacity (a) to investigate the validity of Beer s Law by varying c, and c2 and noting whether equation (11) applies, and (b) for the determination of an unknown concentration c2 of a coloured solution by comparison with a solution of known concentration c,. It must be emphasised that equation (11) is valid only if Beer s Law is obeyed over the concentration range employed and the instrument has no optical defects. 

A useful measure of the strength or intensity of the colour of a dye is given by the molar extinction coefficient (e) at its 2max value. This quantity may be obtained from the UV/visible absorption spectrum of the dye by using the Beer-Lambert law, i.e. 

We must first appreciate that a coloured species such as capsaicin has indeed adsorbed otherwise, there would be no layer to see. And a higher concentration of capsaicin yields a more intense colour as a straightforward manifestation of the Beer-Lambert law. We discern a relationship between the strength of the curry (by which we mean the concentration of the spices it contains) and the colour of the adsorbate, with a strong curry containing more spice and imparting a more intense colour. Conversely, the amount of dye adsorbed on the pan will be relatively slight after a mild curry (which is more dilute in the amounts of hot compounds it contains). 

Examination of beer includes, in addition to observation of its external characters (smell, taste, colour, clearness, formation and retention of froth or head ), determinations of the essential components and of any substances formed by alteration of the beer itself or added as adulterants. 

One way in which most polymers do decay is by the action of oxygen in the air and of light You will be familiar with the way that some polymers go yellow after a time and some become brittle. Coloured plastics, in particular, absorb light and oxygen-induced radical reactions follow. The polymer becomes too cross-linked and loses flexibility. One ingenious application of this natural process helps to degrade the polythene rings that hold cans of beer in packs. These are often discarded and decay quite quickly because some carbon monoxide has been incorporated into the polyethylene to make it more sensitive to photolysis. 

The malt, which is rich in colour, is free of amylase it is a good foam builder and is used mainly for the flavouring of malt and bock beers. Light caramel malt is produced through a similar process however, it is dried at a low temperature after starch conversion. It is still enzymatically active, lightly coloured and increases the mouth-feel and foaming properties of beers produced from light malt. 

Coloured malt is produced by roasting of kiln-dried malt without prior saccharification at a temperature of 190-220°C. It is used to increase the colour of dark beers. The ground malt is dispersed in water, a process which also causes a hydrolysis of starch and other malt components through the malt enzymes. By means of filtration, these flavours are gained in a fermentable, clear solution which is then cooked for the flavourisation with hop. 

In the clarification of beer by cross-flow microfiltration the paper by Trag rdh and Wahlgren [58] seems to be one of the sporadic examples of this application. Here the use of 0.5 xm membranes (Membralox) is necessary to maintain the taste of the beer 0.2 pm shows an unacceptable retention of proteins and colour. Bacteria were retained by the 0.5 pm membrane. 

The value of e (under the conditions specified in Procedure) is 5.2 10" (a=1.9) at 545 nm. In the absence of acetate buffer, e values can be higher [16,17]. Hexamine buffer is recommended. The absorbance of the free reagent is insignificant at 545 nm. Solutions of the CAS-Al complex do not obey Beer s law. The intensity of the colour of the complex depends on the concentration of CAS. The colour weakens with increasing concentration of acetate. Alkali-metal salts affect the colour and its stability. To compensate for this salt effect, corresponding amounts of the salts should be added to the reference calibration solutions [19]. 

An even more pervasive difficulty connected with the average photon trajectory (xiy 2) is absorption and scattering. We re-write Eq. (8) for an exponential absorption coefficient in the form of Beer s law for a series of coloured species having molar concentrations c and (at a given wave-number) molar extinction coefficients e ... 

Gamma radiation has proved to be effective in the sterilization of certain foodstuffs but when applied to beer, the colour, aroma, and flavour suffers. This may be due to the production of peroxide, especially if the content of oxygen in the head-space is high. Radiation methods for sterilization of beer are not permitted in many countries. Other methods such as treatment with ultra-high frequency vibrations or ultra-sonication have not been fully evaluated. 

The total carbohydrates remaining in beer can be estimated as the colour produced by anthrone in 85% sulphuric acid [30]. For a range of beers, values between 0-89-5-98 % w/v as glucose were found [31]. Fully attenuated low carbohydrate lite beers, which have been brewed in the past for diabetic patients, are now generally available with carbohydrate contents between 0-4-0 9% w/v as glucose. 

The ASBC also use a spectrophotometric method and define beer colour as 10 times the absorbance of beer measured in a 12 7 mm (0-5 in.) cell with monochromatic light of wavelength 430 nm. The absorbance at 430 and 700 nm is measured. If the absorbance at 700 nm is equal to or less than 0 039 times the absorbance at 430 nm, the beer is judged free of turbidity and the colour calculated from the reading at 430 nm. Otherwise the sample must be clarified before the colour can be measured. Comparisons of wort colours on EBC and ASBC mashes of the same malts gave the following regression equations ... 

Fig. 22.4 Influence of bottle colour and beer colour on relative turbidity [177],...

Yet another use for casein is for stabilisation, colour removal and clarification of beer and white wine [85,86]. Casein is listed as a component of various dietary and infant foods [87,88]. 

Another, similar, application of activated carbons is in the treatment of edible oils and fats to remove undesirable components. Here, they are used in conjunction with certain bleaching clays. Activated carbon are also used in treating wines and spirits to remove any traces of fusel oil. In the production of brandies, they are used to remove undesirable flavours and to reduce the amount of aldehydes in the raw distillate. In the case of beers, activated carbons are used to improve their colour, and to remove flavours attributed to phenol and colouring matter. 

The principle of the automated UV titration is illustrated in Fig. 4-4. Suitable wavelengths are 450-470 nm for the I3 colour and about 660 nm for the colour of the starch indicator. Initially, the absorption of the 13 solution is beyond the validity of Beer-Lambert s law depending on the type and adjustment of the photometer. When the thiosuphate addition approaches the endpoint, the absorbance-thiosulphate addition relationship becomes linear. The piston increments of the burette are reduced (indicated by an expanded scale in Fig. 4-4) and data pairs of mL of thiosulphate added and relative absorbance are recorded. Regression lines are fitted (by computer) to the linear sections of the titration curve before and after the equivalence point. The equivalence thiosulphate addition is indicated by the calculated intersection of the regression lines. 

The optical properties of analytes can be evaluated in many cases to obtain concentration-dependent chemical signals without a mediator. The term mediator is used here to characterize a chemical receptor which forms an optically active reaction product in contact with the sample. If the analyte itself is optically active, i.e. if it appears to be coloured in visible Ught, then the concentration of the coloured substance can be evaluated by means of Beer s law (also Beer-Lambert law) given by Eq. (8.2). The law is valid for monochromatic light only. Discrepancies occur if the spectral width is too broad to speak about monochromatic radiation ... 

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