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Help - Stones and Foreign Debris in Coffee

Opening a pack of coffee beans to make freshly ground coffee is usually a pleasing thing to do, as you watch the beans spill out of the pack, breathe in the wonderful aroma, and anticipate the enjoyment to follow. However, it’s not so good if you are shocked to discover a small stone or other piece of foreign matter lurking amongst the beans; or worse, you don’t discover it until your bean-to-cup machine or grinder starts making odd noises. In the coffee world, it’s an unfortunate fact of life that on the rare occasion, a small stone of a similar size, shape, or weight as a coffee bean may slip through the net and end up in a bag of roasted beans, regardless of their grade or quality, and despite the coffee being inspected at various stages of processing, and the best efforts of the roaster.

So how can this happen?

Coffee processing is carried out a number of ways in different countries, but usually, after harvested coffee cherries have been sorted and stripped of their outer layers, they are left out to dry in the sun, before being hulled, graded, and bagged for export. In some countries cherries are spread out to dry on concrete patios that are liable to wear and crumble in hot and wet weather conditions, or sometimes laid out on tarpaulins next to roads or dirt tracks. The parchment-covered beans must be regularly turned or raked, and it’s inevitable that small pieces of matter, like small stones, limestone, or volcanic rock, will get mixed in with the coffee when it’s raked or swept up.

Although it seems there’s no way of making sure bags of coffee beans are completely free from stones or debris, many coffee producers are working to improve their processing methods, such as by using elevated mesh drying beds to help to remove stones etc. from the mix. There’s also less chance of debris when the coffee is turned by hand rather than raked, as anything unusual is easier to spot. Stones may also be detected and removed by hand when the beans are bagged for export.

Once the green beans reach the roaster, other quality control measures come into place. At Coffee-Direct, our coffee roasting process includes a destoner facility that works like a vacuum cleaner, and is set to lift the weight of a coffee bean, but not stones which are usually much heavier. Unfortunately some of the stones found in raw coffee are volcanic and therefore quite light, so may possibly get lifted up with the beans. Coffee beans are also visually checked when being weighed.

Coffee is a natural product and it’s inevitable that foreign materials will sometimes be mixed up with raw beans, which is why many electric grinders, including those in bean-to-cup machines, feature a reverse gear to allow for this without incurring damage. However, if you think your bean-to-cup machine or grinder could suffer, it may be prudent to cast an eye over your beans before they go into the hopper rather than risk damage to the grinding plates or blades. Obviously it’s easier to spot something odd in a small measure of beans, but pouring a larger amount first onto a large white plate or chopping board may help to identify possible culprits before they can do any harm.