What is UV light? (shop)
“Ultraviolet (UV) is a form of electromagnetic radiation with a wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and radiation is about 10% of the total electromagnetic output from the Sun. Although long-wavelength ultraviolet is not considered ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules” Wikipedia
Humans can only sense a portion of the electromagnetic spectrum, referred to as the “visible light spectrum”, for some reason. The rest, such as infrared at long wavelengths (greater than 760nm) and UV at short wavelengths (more than 380nm), are observable to other creatures. Except in the case of UV light, humans require specific equipment to comprehend it. Fluorescence can alert us to the existence of UV light in the presence of substances like phosphorus.
Coffee bean fluorescence (cart)
Fluorescence is the concept behind those unpleasant, noisy tube lights (fluorescent bulbs). The electrical discharge between the two electrodes produces ultraviolet (UV) light with a short wavelength that is invisible to us. This UV light then passes through a coating on the bulb (often a phosphor), which absorbs some of the UV’s energy and attenuates the high-frequency magnetic waves before re-radiating them at low frequencies. additional information: visible light
Blacklights are created in the same way as incandescent and fluorescent lamps, but the glass housing and coating are made of different materials. This means that most light released is UV, with only a tiny amount of visible light near the UV spectrum (indigo and violet). As a result, ultraviolet lights are typically dark blue or purple.
So now we know what UV light is and why some coffee beans can “glow” when exposed to it. But the most pressing question is: why are low-quality (or allegedly low-quality) coffee beans able to glow under UV light? And, last, what can we say about these beans – Under UV light, this determines how we classify coffee. But first, use an ultraviolet lamp to sift coffee.
Using UV light to sort coffee beans
First, you’ll need an ultraviolet light (which may be easily acquired online), a dark place, and the coffee batch to be tested. After that, shine the light on your coffee sample right away. Slowly adjust the light up and down until the luminous coffee beans are visible.
In the light, different types of coffee will appear differently, but within a batch, everything will look the same; only the defective (or problematic) beans will stand out with their luminosity, which will vary depending on the level degree. Pick up any entirely luminescent particles, as well as any speckled, dotted, or partially luminescent, and sort them out separately (we’ll break them down later).
Turn the lights back on and analyze what you have after making sure there are no anomalies in the batch of seeds and that you have selected all of the poor seeds. Small, underdeveloped, perforated, discolored, and chipped or shattered seeds are common visual abnormalities.
The effect of coffee processing on its brightness
Many coffee chemicals include phenylalanine, tyrosine, protein, p-coumaric acid, caffeic acid, ferulic acid, chlorogenic acid, nucleic acid, theobromine, quinic acid, caffeine, and scopoletin, reflect blue under UV light. Other molecules in coffee can absorb or screen UV rays; because UV rays can cause harm at the cellular level, plants require protection from the sun’s UV rays (from annual reviews).
However, based on Christopher Feran’s research, there are some physical facts that luminous coffee beans, whatever the reason, tend to:
- Lower density (by a factor of ten).
- Reduced humidity (lower water activity).
- The color has faded considerably, and they are frequently damaged.
On the other hand, UV grading becomes erroneous after a lengthy period of storage since the fluorescence of coffee beans dramatically decreases with time. Because neutral lipid hydrolysis increases the concentration of free fatty acids, which will bind to fluorescent chemicals, phospholipids in coffee steadily decrease with time. So for fresh coffee, the UV rating is the most accurate — the newer, the better (from onlinelibrary.wiley.com).
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The rate of fluorescence is increased when coffee is not properly dried
When coffee dries too quickly (because of excessive heat), it kills the embryo and potentially the endosperm tissue first. Then, many intracellular chemicals transfer from the inside to the outside of the interstitial space, cell wall and plasma membrane (cellulose septum). Microbial and enzymatic activity may also play a role in highly humid environments, increasing exposure to air and resulting in oxidation and UV luminosity. Fermentation of Cocoa and Coffee, p.386).
Overfermentation resulted in fluorescent beads
When exposed to UV light, some faults that are difficult to notice with the human eye, such as seeds damaged by moulds or bacteria (Streptococcus strains), glow. We can use this characteristic to classify “stinkier” beans (those with sour kernels or those that have been over-fermented), as previously mentioned (Espresso Coffee, p.107-108).
Over-fermented seeds glow white or bluish-white under UV light, indicating a higher concentration of free caffeic acid than healthy seeds. It’s worth noting that caffeic acid is a precursor of ferulic acid, which is luminous (Espresso Coffee p.130).
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UV protection and grain quality
We can see how crucial it is to use UV lamps to lower the percentage of faulty coffee to attain superior quality (and at a better price). However, the only way to make this information genuinely valuable is to share your green coffee analysis expertise and procedures with growers and farmers so they can spot any problems right away.
Be aware that many people lack the financial means to purchase modern optical sorting equipment; our goal is to improve access to instructional materials and technology that can enhance the quality of coffee and the lives of those who create it. Because a UV lamp is less expensive than a roaster, the percentage of seeds lost due to UV grading may not be a significant issue. However, even with a lot of workforce and money, it is still impossible to totally eliminate obvious faults with UV lamps at the production level.
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