Sampling Methods
Coffee is usually laid out in thin layers on raised beds or concrete patios to dry. If the layers are too thick, the beans won’t dry as quickly and will be at increased risk of mold.
Raised beds allow the wind to circulate more than concrete patios, which can further aid consistent drying. In both methods, the beans are moved around regularly to allow air to circulate.
One way to ensure that the beans are drying consistently and at the right speed is to take regular samples and measure the moisture content.
But it’s not enough to simply take some beans at random and check how dry they are. Instead, you should create a sampling plan that focuses on comparing representative samples.
After laying parchment coffee out in beds, wait a week to start sampling. Then, measure the moisture using a meter. Do this every day in the morning and at the end of the afternoon until it has humidity between 14 and 15%.
How long this takes varies with how the coffee was processed and how the beds are positioned (fully or partially exposed to the sun).
The Cone Method
This technique involves creating a cone-shaped pile of coffee beans not less than 1.5 kg. Randomly take samples from five to eight dispersed sites on the drying bed until you have around 1.5 kg.
Pile them up and flatten the top. Then divide it into two, and then four equal parts. Reject two piles diagonal to one another and mix the remaining two. You should have a pile of at least 300 g of beans. Use a moisture meter to test the level of humidity and record it.
Sampling Bagged Coffee
When parchment coffee beans reach around 12% moisture, they are usually bagged in burlap or water-resistant bags and stored until milling. During storage, the beans are at risk of taking on more water so it’s important to keep them in a dry, cool, and low-light environment and to keep monitoring moisture levels.
Select samples from three different areas of each bag (not all from the top or the bottom), and check that they are representative. That is, consider whether they appear uniform and free from defects. Then use the cone method to check the percentage of moisture. If the parchment measures above 12% humidity, consider drying it further on beds, patios, or in a mechanical dryer.
So far we have only discussed parchment coffee, but green coffee beans (that is, beans with the papery parchment skin removed in hulling) more easily absorb moisture from the air. So there’s a greater risk of green coffee taking on moisture during storage. For this reason, it’s even more important to keep green coffee beans in a dry, temperature-controlled location.
If green coffee has a humidity greater than 12%, it’s an indicator that it wasn’t properly dried or stored. You can’t simply put green beans back on beds to dry for longer because it can damage the grain. So make sure to set up a sampling schedule and keep green beans in the correct conditions.
Tracking Moisture Levels
Record the humidity level each time you take it to keep track of whether the beans are taking on more moisture over time. This will help you identify whether there are problems in your drying method or storage space.
With bags of parchment coffee, measure the humidity three times a month. With green beans, measure twice a week. This will allow you to quickly move the bags to better storage conditions if you see any increase and try to prevent further spoilage.
Bags of green or parchment coffee should have identification labels and detailed records. For full transparency, record the following for each bag:
Date that the coffee entered storage
Temperature of the warehouse or storage space
Weight
Lot number
Processing method used
Percentage of initial humidity (the humidity measurement when it entered the warehouse)
Dates of sampling, the quantity sampled, and the measurement of moisture content in
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