Colour is the human perception of a physical phenomenon. Our brains interpret how different wavelengths of light interact with objects in the world around us through emission, reflection, absorption, and transmission.
Because colour can be objectively measured with quantity and wavelength of light, it is possible to measure and interpret it with specialised equipment, just like how our eyes and brains interact with each other. Hawkins Watts has several pieces of equipment to help with colour measurements, allowing us to better match colours when problems arise, such as ingredient changes or supply issues. We can then use the extensive library of products from our colour supply partners Cathay and DDW to find the best solution and create custom blends.
Relevant Theory for Matching Colours in Food
When discussing colour and colour measurement, it is vital to understand how it relates to the visible light spectrum or electromagnetic waves within the range of 380nm to 700nm. Red light has the longest wavelength, and blue-violet has the shortest.
The way light interacts with a portion of food is critical to the way we perceive its colour. For example, 50ppm of tartrazine will look very different depending on if it is dosed into milk or water. Therefore, it can be important to consider the base formula’s transparency and opacity when matching colour, as it also informs the best equipment to use to measure colour.
Since foods are natural products, they tend to exhibit a combination of different light interactions. These combinations can be complex to map and explain. For example, the artists at Pixar making the film Ratatouille had to create entirely new programs to properly animate the way light interacts with food.
The following terms are descriptors for the different interactions that determine a food’s visual characteristics.
Absorption – Light is absorbed into many pigments, preventing it from hitting our eyes. If all wavelength is absorbed, the food will appear black. Likewise, absorption of specific wavelengths but not others result in a coloured product.
Reflection - is the inverse of absorption. When light is reflected off an object and hits our eyes, we perceive that colour. If all wavelengths are reflected, the food will appear white.
Transmission - of light occurs when light passes through an object rather than being reflected. It applies to transparent products, like soft drinks or jelly. When specific wavelengths pass through, and others are absorbed, the resulting colour will correspond to the transmitted wavelengths.
Scattering – sometimes wavelengths of light in the visible spectrum bounce off suspended particles in a food system, whether an emulsion or a colloidal suspension. This results in a hazy or cloudy appearance. Shorter wavelengths (eg, blue) are more likely to be scattered, resulting in a bluish haze to many suspensions.
The first piece of quantitative colour measurement equipment Hawkins Watts has is a UV Spectrophotometer and corresponding computer software. This equipment is valuable when colour matching, shelf-life testing, standardising natural products and running quality control.
Spectrophotometry measures the absorbance and transmission properties of a coloured liquid as a function of wavelength within the visible light spectrum. The coloured liquid must be entirely transparent for optimum results. A diagram of a spectrophotometer setup is shown below.
Light is either transmitted through the sample solution or absorbed. The photocell can detect the amount of each wavelength that hits it and therefore measure transmission and absorbance by the sample. This can be very useful for determining the strength of a colour when compared to a reference. Examples include the percentage of colour degradation over a product’s shelf life or the exact pigment content in a natural product like fruit juice. All pigments have a specific absorption spectrum (like in the below image), which can identify the type and quantity of certain pigments in food. To ensure the transparency of solutions, the best solvent for any given pigment should be used, whether that is distilled water, pH 3 or pH 5 buffer, ethanol, or acetone.
Hawkins Watts has a Konica Minolta Colorimeter, which allows quantitative colour measurement of translucent and opaque liquids and solids, in addition to transparent products (where a standardised white backdrop is used). This makes it more versatile than a spectrophotometer, although results are purely comparative and less able to be interpreted into a pigment concentration or difference in colour strength.
In colorimetry, measurements are made using the CIE L*a*b colour space, a three-dimensional graph that allows a colour to be plotted in terms of lightness, red-green shade, and yellow-blue shade. The total colour difference between two colours in the 3D space can be calculated; this value is referred to as ΔE. Values of greater than 2 are usually noticeable to the naked eye.
Typical applications that use the colorimeter for matching are dairy products, fat-based products (like chocolate or crèmes), sauces, or even non-homogeneous products like bakery items. Colorimetry can be used for quality purposes outside of colour matching, for example, measuring the roast level of coffee beans, the ripeness of fresh produce and the freshness of meats. Additionally, a colorimeter can help us find alternatives for other ingredients, such as Dutch processed cocoa powder.
How Can We Help?
A colorimeter and spectrophotometer allow us to take the guesswork out of colour matching, by using a scientific approach. Changing the colour of processed foods can be complex, without even considering issues with stability, solubility, and regulations for different food pigments.
We can help you reach the exact colour you are targeting using our library of high-purity synthetic colours from Cathay and natural colours from DDW. We even measure the change in colour throughout a product’s shelf life to help determine the best solution.
So, if you’re working on a new product or a raw material change that affects the colour of your product, please don’t hesitate to get in touch.
Elise Waddell – firstname.lastname@example.org
Alan Bulmer – email@example.com
Shahab Moradi – firstname.lastname@example.org