Today we’re just touching the tip of the iceberg that is the process of a coffee bean from the farm to your cup, but grading and screening is an important aspect of that great taste that you love!
As specialty coffee roasters we continuously strive to find the best quality green coffee beans because we care about consistency, quality and purchasing ethically.
As roasters, our biggest concern with consistency is that coffee beans are consistent in size and quality within a lot.
Larger beans roast slower than smaller ones, so it’s difficult to get a consistent roast if there are different sized beans in the same selection. We don’t just want good-sized beans; we want beans that were carefully sorted by size and quality.
There are quite some things involved in this! Screening for size and grading for quality.
Consistency in size comes down to screening the beans.
Before being exported from its originating country, coffee is screened.
Processors use screens to sort the beans by size. The beans are sifted through these screens, which are metal sheets with specifically sized, round holes punched into them. Screens are numbered 8 through 20, with the number referring to how many 64ths of an inch the holes are. For example, a size 8 screen has holes that are 8/64 inch wide, and a size 20 screen has holes that are 20/64 inch wide.
The size of a selection is determined by passing it through screens until it doesn’t go through the next-smaller size. For instance, if a coffee passes through a size 18 (18/64 inch) screen but not a size 16 (16/64 inch wide), it’s graded as size 18. This measurement is rarely perfect, so some leniency is allowed for larger and smaller beans. In its classification, the SCAA permits a 5-percent variance; other organizations allow similar or smaller variances.
Traditionally, even-numbered screens are used for Arabica selections, and odd-numbered screens are used for Robustas. Therefore, an Arabica lot that was graded at screen size 18 might technically be 17/18, since the next-smallest screen used for Arabicas is usually size 16.
The quality of the coffee comes down to defects in the beans. Green coffee is often graded according to the seriousness of the defects.
The Specialty Coffee Association of America (SCAA) has gone some of the way to establishing a widely applicable grading system with its Green Arabica Coffee Classification System.
The SCAA has described a number of imperfections that may affect the quality of the coffee and the number of defects – there are both primary defects and secondary defects – are measured in a coffee sample of 350 grams.
A primary defect would be something like a ‘full sour’ bean, where the coffee has been overly fermented, or organic matter (like sticks) mixed with in the coffee, while a secondary defect would be something like a broken or insect-damaged bean.
Using the SCAA system the coffee can then be graded from one to five, with specialty coffee with no primary defects being Grade One. Although there are five grades, the SCAA is only concerned with the top two – specialty coffee (Grade One) and premium coffee (Grade Two).
Exchange coffee (Grade Three), Below Standard Grade Coffee (Grade Four) and off-grade coffee (Grade Five) have very many defects and lack much of the flavor of the coffee you are probably familiar with.
SCAA grading scale:
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.
At the Atlin mountain coffee roastery we only purchase grade 1 arabica coffee beans (with exception of Ethiopian which is grade 2). Also, some of the beans we import are hand picked 3 times (Sumatra Mandheling), meaning people have sorted through the beans 3 times to remove any beans with defects!
So next time you drink your Atlin mtn coffee, hopefully you’ll be able to appreciate (if not just a little bit more) all the things that go on behind the scenes that we take care of to ensure the best of flavours, quality and consistency!