Among the various ingredients used for beer production, beer colour is determined primarily by the selection of the grains used in formulation, and more specifically the type of processing these grains have undergone. Like stock creates the base of every great soup, malt provides several key attributes that define beer , including colour, flavor, body, and, eventually through fermentation, alcohol.
Yeast does not contribute to beer colour directly, other than colour loss during production via adsorption of coloured materials to their cell wall. Indirectly, yeast can affect beer colour via turbidity in products where it remains present at packaging, such as with hefeweizen.
Barley contains very low concentrations of pigmented substances, and it is the malting process that results in colour formation. The germination and kilning phases of the malting process set the stage for and determine the extent of colour formation from Maillard browning reactions and in some cases caramelization and pyrolysis reactions. Secondary to these heat driven color-forming reactions, the oxidation of polyphenols derived from barley husk or hop vegetative matter can contribute to colour formation during beer storage/ageing. Additionally, oxidation of polyphenols can lead to enhanced protein–polyphenol interaction and the formation of non-biological haze. The scattering of light via this haze indirectly affects a consumer’s perception of colour as well as its physical measurement.
Colour is a human visual perception utilising a narrow portion of the electromagnetic spectrum (380–780 nano meters). Light itself has no colour and colour does not exist by itself , it only exists in the mind of the viewer . Colour perception exists in two stages. The first is a purely physical phenomenon that requires three elements: a source of light, an object and a detector (an eye, a diode, etc.) while the second stage is a complicated and incompletely known process whereby the human eye transmits information that the brain will interpret as colour.
The principal attributes of any object’s color are hue, lightness and saturation.
1. Hue is the quality we normally identify as an object’s colour, such as red, green, yellow and so forth. Hues form what we describe as the colour wheel. The human eye can identify more than a million different hues .
2. Lightness is a term related to the concept of light and dark and is used to classify colors by separating those that are bright, mid-tone or dark.
3. Saturation or chroma is completely separate from hue and lightness. It can be defined as purity of colour; that is as a colour moves away from a central neutral Gray its saturation increases as it becomes more vivid and less dull.
Often these three color attributes are described.
What is Light?
What is colour ? What cause Colour ?
colored light comes to the eyes in the following ways
1) Directly from a light source.
2) Light reflected off on object
3) Light transmission through the object.
For Secondary Sources, Interaction of Primary Light and Secondary Source is Very Important
In case of beer white light is transformed into yellow and blue when absorbed.
Measuring Beer Colour
Historically, beer colour was determined by visual comparisons against a set of colour standards. Joseph Lovibond developed a set of standards and a tintometer in 1893 while solutions of potassium chromate have been used as reference standards in the early 20th century. The use of standardised Lovibond coloured glasses made it possible to compare measurements from different Lovibond Tintometers. After a series of modifications, these standardised comparator discs were accepted by the European Brewing Convention in 1951. So ingrained was this approach that many brewers and maltsters today still refer to color values in degrees Lovibond. The tintometer approach, while satisfactory at the time, had inherent flaws due to variation in color perception by the human observer. Because red-green colour blindness is present at roughly 7% of the male population. Furthermore, instability of the glass or liquid colour standards over time, for instance orange dichromate slowly reducing to green chromium , would lead to false color estimates.
The solution to both of these issues was single wavelength measurements using a precision spectrophotometer.
A beer colour is measured in Standard Reference Method (SRM) or European Brewery Convention (EBC) Units. SRM is based on Lovibond scale and determined from a wort analysis. this is a spectrophotometer measurement, does not indicate hue, only depth when viewed at a wavelength of 475 nanometers.
A white shade of 2 SRM
Orange / Tan of 10 SRM
Red / Brown of 20 SRM
Mahogany or black of 30 SRM
Various Spectrum of colours
In addition to pH, the Maillard reaction is principally driven by time and temperature and modulated to a lesser extent by moisture. In the range of 60–100 ° C, an increase of 1 ° C can increase the rate of the Maillard reaction by more than 10% . Increasing heat exposure to higher temperatures promotes the production of more advanced Maillard reaction products because of their higher energy of activation thus resulting in greater color formation.
Maillard browning reactions are key to beer colour and they originate in the barley endosperm during malting but can resume during wort boiling. The two key components of this reaction are reducing sugars (principally maltose) and free amino acids or amino groups of amino acids that comprise protein.
Colors produced by melanoidins are yellow, orange and red initially and turn to brown as the Maillard reaction is allowed to proceed. Lightly kilned malt displays yellow colors characteristic of light lager beer while intensely kilned products display amber and brown hues characteristic of British ales or Vienna lagers.
Colouring agents such as malt extracts and caramel colouring can be added post-fermentation as a means of adjusting the beer’s final colour. These products are intensely coloured with colours ranging from 250 to 3500 ° SRM for concentrated malt extracts and 5000 to 30,000 ° SRM for caramels.