The evaluation and grading of green coffee beans is an important step in ensuring an excellent final cup of coffee. Only the finest quality coffee beans should be used for the preparation of extraordinary coffee drinks. Excellent roasting and brewing practices combined with poor-quality coffee beans will not create memorable coffee experiences.
Specialty coffee roasters usually display quality grading terms on the labels of their coffee bags. We may find grading terms such as Kenya – GUAMA AA. AA is a grading term defining a specific and large bean size. Other grading terms we might see on the label are SHB (Strictly Hard Bean) or SHG (Strictly High Grown).
There is no universal standard method for grading and classifying green coffee beans. Coffee growing countries have developed their own classification systems that are usually based on some, or all, of the following criteria:
Preparation method (wet vs dry)
Bean (screen) size
Bean shape and colour
Number of defects
To ensure excellent roasting results, the beans also need to have a uniform size.
Green Coffee Classification System
The Specialty Coffee Association of America (SCAA) has established its own Green Coffee Classification System. The beans are graded according to the bean size, colour and percentage of imperfections found in random samples. To identify the quality of processed green coffee beans professionals are taking advantage of precise spectrophotometric tools.
According to SCAA there are 5 grades (qualities) of green coffee beans:
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.
Source: here (Green Coffee Classification System Poster from the Specialty Coffee Association of America)
There is a correlation between the coffee bean size and the altitude of the plantation. The higher the altitude of the plantation is, the larger, more dense and harder the coffee beans tend to be. Generally, harder and larger coffee beans are sweeter and possess more intense flavours.
Coffee plants that grow on high-altitude plantations are exposed to less oxygen. Therefore, their fruits take more time to mature. That way, they are developing more complex sugars.
Green Coffee Beans Sizing Chart
The WS of the Coffee Research Organisation provides an international Green Coffee Beans Sizing Chart which displays how various coffee growing countries classify and compare coffee beans by using a screen size sorting system: here
The Challenge of Grading & Understanding
Sweet Maria’s (a Coffee Warehouse and Green Bean Supplier in Oakland, CA, USA) finds it very challenging that almost every country of origin has its own grading scale: ‘It can be incredibly confusing. Sometimes the coffee earns a higher grade than it deserves, sometimes the grade is actually lowered to avoid tariffs! Central and South Americans tend to follow the SHB and SHG model (Strictly Hard Bean and Strictly High Grown indicates altitudes above 1000m). So hard beans grow at higher altitude and that’s good, right? Well, in Brazil’s grading, Strictly Soft is a top grade. Many countries use a simple numeric scale. But a Grade 4 Ethiopian is the top Dry-Processed grade you’ll see (Gr.2 in washed Ethiopians), and a Grade 1 Sumatra DP allows 8% defects (in fact Sumatra Grading is based on cup quality)! In essence, all should conform to the Green Coffee Classification System, but they don’t.’ See: here