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It all comes down to what the scale says!

Coffee is a story of mass conversions. At every step of the supply chain, scales and their calibration are heavily relied upon to determine the transaction between buyer and seller. The global coffee industry functions entirely on the basis of weight. The ICO indicator price at the time of writing this is $1.58 per pound or in other words, $3.48 per kilogram. But! Is your pound the same as my pound? Or more importantly - what makes a kilogram a kilogram anyway?

"All scales should periodically be calibrated with traceable standards to ensure they haven’t drifted over time to which could give inaccurate and unreliable readings."

- Ian Torres a Metrologist for Boeing Company in Washington State

Photo: NIST headquarters in Colorado by

Traceable standards are standards that are certified and can trace as far back as the global standards do. Up until recent history, these standards would trace back to a physical artifact. One example is Le Grand K. Le Grand K was originally forged back in 1879 to officially define the Kilogram. It is secured and locked up in a vault just outside of Paris with three separate keys to unlock the vault.

Photo: Le Grand K replica by Reuters

Le Grand K is made up of 90% platinum and 10% iridium. These materials were used due to their density and resistance to change over time. However, at the last weigh-in, it showed that Le Grand K had lost 50 micrograms since 1879.

For context and as the saying

"light as a feather" goes:

The average feather weighs 164 times as much as what Le Grand K lost in roughly 129 years of service.

At the 21st meeting of the CGPM (General Conference of Weights and Measurements) in 1999, national laboratories were asked to find new ways in order to break the link between the kilogram and this physical object.

Scientists eventually broke that link, and in 2018, voted unanimously to replace the standard of Le Grand K with a new and better constant the following year. This new SI Base Unit relates the kilogram to the "mass equivalent of the energy of a photon at a specific frequency."

Or for you super nerds out there:

"The kilogram is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs."

Uhhh, what?

In other more practical words:

The new KG standard uses the Planck Constant - a phenomenon in nature... which is directly important for Quantum Mechanics... and is now indirectly important to coffee.

Yes, coffee. That's right. That's what this was all about.

Photo: green coffee ready for export in Thailand

Due to the nature of the business in coffee, I always make it a point to encourage individuals to analyze costs, forecast losses, and data log their own conversion averages and/or turnout numbers. Oftentimes, and as a way to simply get started, I will recommend utilizing resources already out there.

Sometimes using numbers derived from this Cenicafe resource here:

However, it's not uncommon for me to see conversion numbers that differ as much as 20-40% from the above resource. It all has to do with the equipment, operations, and raw materials a facility has. This is why it is so crucial to begin gathering the data as soon as possible and to formulate your own conversion numbers. Not only does it give you better planning strategies for meeting customer demand, but also provides invaluable insight as to where your operations in post-harvest processing can improve.

The great thing is you don't need much to get started. A pen and pad works great. Google sheets - even better. And of course the most important part of all:

A Scale.

One that is accurate, reliable, AND properly calibrated to the international standard that I covered above. A scale that also has the ability to tare and zero would be immensely helpful.

Gather weight data any time the mass of the same lot of coffee changes.

(e.g. from fruit to pulped, or from the first day to final day of drying, or dried parchment to green or even green before and after sorting)

In the coming weeks, I plan to put out a resource in google sheets whereby users can follow the steps and tips provided and will be able to input their own sample coffee weight data at various processing intervals. Eventually aggregating their own custom conversion averages. I hope the tool will be useful for some of my students out there. Perhaps not and it will be a waste of time. Either way, I'll have fun making it.

Thanks for reading.

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