Dry Processing

When the dried parchment beans are transported over to the dry mill, they are ready to mill. At 11% moisture, parchment coffee is considered a grain and has a crunchy feel to it in your hand. The parchment coffee also smells like a grain. The Huller and Polisher has a worm drive component to it that actually smashes the beans against each other while vacuuming out the crushed paper flakes that once was the parchment skin. The Huller and Polisher also removes a chaff, which we call a silver skin. This helps keep the roasters clean. After the Huller and Polisher has done its job, we reveal the clean, dense, coffee-green color green bean. Green bean is ready to be roasted.

This is Mountain Thunder's Huller Polisher.
Mountain Thunder's sizer in the Dry Mill. Notice the eight screens or sizes that the sorter sorts.
Mountain Thunder's Gravity Table. This machine sorts away heavy beans from less dense beans.

Nevertheless, in Kona we have rigorous quality control and certification standards which are built into Hawaii State Law. This form of social control ensures that our Kona Coffee is of a sufficiently advanced grade which adds to the unique flavor of Kona Coffee. Where European nations and Japan have import regulations which protect the consumer, Hawaii has export regulations which do this.

In the dry mill at Mountain Thunder we prepare three mixtures of beans for our Roasted Coffee Products, our Estate-Origin coffees will be an all-size mix from 16/64 in. to 19/64 in including peaberry beans we certify this coffee at a Select grade (allowable 5% defects by weight). However, many times the actual % defect rate is 1-2 percent, which is very clean for being certified Select in this case. We also process green bean for our Private Reserve and our Premium coffees. Private Reserve is a unique blend of size 18 screen and 19 screen coffee sorted by color down to less than 1 percent defects. Premium is the same only that it uses size 17 screen and 16 screen beans. For both Premium and Private Reserve, we certify the coffee to Select Grade. Again, although we are allowed 5% allowable defects, we bring Premium and Private Reserve green coffee mixtures to below 1 % defects. We also use Peaberry screen, with its special oval screen which sorts away peaberry from the rest of the crop.

Note the machines that we use to create these grades of Kona Coffee. See the pictures below to see the sizer, which is a series of 8 screens that shake back and forth to sift and size the coffee. You can see the gravity table, which separates the Kona Coffee with defects such as chips and pieces from the wholesome dense and heavy beans. And of course, the optical color sorter which uses an advanced optics system to sort away the black, white, brown and yellow beans from the coveted coffee-green color beans.

Mountain Thunder’s Color Sorter

Above, we describe how the green beans are sorted to go into Mountain Thunder’s roasted products, however, the official state certification standards go from Extra Fancy, to Fancy, Number One, Select and Prime. The percentage defect rates respectfully are less than 1%, less than 1%, 3%, 5% and 15%. These grades are established for the green coffee broker / commodity relationships to maintain a quality standard. Mountain Thunder sells very large sizeable portions of the lower grade Prime to other roasters of 100% Kona Coffee. This lower grade, prime coffee will end up being sold in bags of Kona Blend across the nation. Mountain Thunder only roasts the best, choice 100% Kona Coffee in its label. All second choice, lower grade coffee is sold to blenders of 10% Kona Coffee.