Coffee bubbles

When a client asked us to measure the size of coffee bubbles, we were naturally rather surprised. Apparently, the fineness of a coffee bubbles is a measure of the perceived quality of the coffee.

According to 2015 figures, after crude oil, coffee is the most sought-after commodity in the world and worth over $100 billion worldwide. That puts it ahead of other valuable commodities like natural gas, gold, oil, sugar and corn. Global coffee consumption has increased 2.5% year on year since 2011, making it one of the world’s favourite drinks, with over 2.25 billion cups drunk every day in various forms.

So how did we apply innovative capabilities to measure bubbles?

It’s all about the lights, camera and action! Without going into great detail, we created a system that started with amazing lighting. The illumination of an object, as any photographer knows, is key to getting a good image. Not only that but by being clever with the lighting it is possible to highlight features you wish to assess. In this case, the coffee bubbles. Our design incorporated state of the art LED lights which could be controlled in their location and adjust the level of illumination to enhance the bubbles or provide good background illumination. 

Dual illumination light rings

With the right lighting, we selected a lens that would not distort the images and provide great resolution using our high-resolution camera.

Camera and lens arrangement

To avoid the steam from the hot coffee affecting the lens, an extraction system was needed as can be seen either side of the lens. To obtain full flexibility the entire system of camera and lighting could be arranged at any desired height with respect to the coffee to get the required magnification.

Operation

The client needed a professional piece of diagnostic equipment to be provided for staff to assess multiple coffee foams from a wide range of coffee machines. The system was designed to be aesthetically pleasing in a laboratory environment and simple to operate. The entire system is illustrated in the following figure.

Laboratory equipment (left) and coffee sample in the machine (right)

The type of images that were captured are illustrated in the following figures. The first is a natural image with reasonably normal lighting. 

The lighting used allowed multiple images to be taken under differing conditions in order to ensure that the image processing process was able to operate accurately and reliably. The two enlarged sections illustrate the dramatic difference by having excellent control of the lighting.

Software

Software was written which took the images and computed the size and shape of the coffee bubbles depending on parameters set up the by the operator. The following example shows how the image can be processed in order to compute statistics about the coffee bubbles. 

User software screen showing the image processing steps to extract bubble statistics

The statistics were then presented to the operator in a histogram format which allowed the operator to make quantitative comparisons between the differing coffee machine bubbles and hence the perceived quality of the product.

Bubble size histogram

Lessons learned

Do it right, do it once. We applied our expertise to create an amazing one-off system, which by clever design and great software gave the buyer a very useful tool to assist them in their product assessment and development in increasingly valuable industry.

Get the fundamentals right and the rest follows. By using the best lighting, lenses and camera with a very flexible geometry we created the right basic information to make the image processing side of the project much easier.

Simple things matter. As for the giant in the coffee industry that employed us, perception of the bubble size of coffee is a key indicator of quality which should not be ignored, in our case the creation of a professional piece of equipment which was very fit for its purpose was the key to having a satisfied customer.

Keep to your strengths but remember they are generic. Why would a company famous for measuring pipes and inspecting welds stray into measuring coffee bubbles? Well it is all good metrology for us and good product design. It keeps our team sharp to be involved other areas and really, what is the difference between a great inspection of a weld with the best lighting and best analysis compared to a cup of coffee – superficially a lot but fundamentally a lot of similarities.