In the world of coffee, the word “grading” has several overlapping meanings. Today we’re going to focus on two: grading as groups of coffee sorted according to quality, and grading as coffee sorted according to size. Both are instrumental processes that happen between the harvest and the roast, and have a huge impact on the eventual quality in your cup.
Immediately after coffee is harvested, it’s processed. Farmers deliver their beans to washing stations (where processing happens) with urgency – freshly harvested coffee begins to sour less than 24 hours after being plucked from the branch. There are several way to process coffee, but today we are going to focus on the one that make our Rwandan beans shine – Wet Processing with Fermentation.
After harvest, coffee cherries are sorted according to ripeness, and then poured into tanks of fresh water, where the good cherries sink to the bottom, and cherries bored by insects rise to the top and are sifted off.
Cherries are then moved to the de-pulping machine, where (the name implies) the flesh of the fruit is removed by rotating blades.
After de-pulping, the beans are coated with a layer of sugars, or “mucilage.” They are washed up to three times to remove mucilage before being moved to tanks to ferment.
After the mucilage has fermented off (a process which takes roughly 12 hours), beans are moved to racks to dry in the sun. This stage is carefully monitored to ensure that the moisture content of the beans falls within 9-13%.
Finally, the beans are sorted by hand according to several factors: color, size, intactness, and obvious defects.
Grading as “Groups”
There are five grades of coffee quality, sorted according to number of defects, and ideal attributes. “Quakers” are beans that died on the tree before harvest, and are shriveled with a papery taste.
“Grade 1: Specialty Grade Coffee Beans: no primary defects, 0-3 full defects, sorted with a maximum of 5% above and 5% below specified screen size or range of screen size, and exhibiting a distinct attribute in one or more of the following areas: taste, acidity, body, or aroma. Also must be free of cup faults and taints. Zero quakers allowed. Moisture content between 9-13%.
Grade 2: Premium Grade Coffee Beans: Same as Grade 1 except maximum of 3 quakers. 0-8 full defects.
“Grade 3: Exchange Grade Coffee Beans: 50% above screen 15 and less than 5% below screen 15. Max of 5 quakers. Must be free from faults. 9-23 full defects.
Grade 4: Standard Grade Coffee Beans: 24-86 full defects.
“Grade 5: Off Grade Coffee Beans: More than 86 full defects.”
The Specialty Coffee Association of America only deals with Grades 1 & 2.
Grading as “Size”
Size is particularly important, especially when it comes to roasting. Large beans will not roast the same way as their smaller counterparts, so a sample with a range of sizes will be unevenly roasted.
In the spectrum of coffees as a whole, higher quality beans will be grown in higher altitudes, by plants that take their time to produce relatively small, flavor-dense beans. However, in a sample where factors such as varietal, altitude, and cultivation are identical, the larger the bean, the higher the quality.
Beans are graded by being sifted through metal screens with holes of specific sizes. The grades are numbered according to the diameter of the holes, ranging from 8 to 20, with the number indicating 64ths of an inch. Grade 16 has holes 16/64in in diameter, Grade 10 is 10/64in, and so on.
Although this method cannot be 100% accurate, a variation of 5% does not have a significant effect on the final batch.
So there you have it! If the “grade” is between 1 and 5 it means “grade as quality,” and if it’s between 8 and 20, it means “grade as size.” While this information digs a little deeper into the guts of coffee knowledge, it significantly affects the quality of your brews.
In fact, we’re celebrating our 10 Year Anniversary with a particularly special blend – and grading has everything to do with it. Keep an eye out for a massive piece of news!
And as always… happy sipping.