The physical appearance of coffee matters. Because besides tasting, you can fully judge a coffee by sight. As you green grade coffee, you can spot quality-harming coffee defects and inconsistencies within a sample. And this gives you the confidence to choose coffees when you doubt the quality.
Green grading is basically a double-check before you buy, roast, and serve your next coffee.
The ‘how to green grade coffee tutorial’ walks you through the steps of green grading and evaluating a sample by sight, all in two-minutes. Want a written step by step guide, scroll past the video, and immerse yourself in the details of green grading.
Before you dive in, a note: as a roaster, you shouldn’t worry too much about green grading. If you are sourcing through reliable exporters and importers, then there’s no need to green grade every single sample. However, when you receive a sample and you doubt the supplier and quality: green grade!
Green grading starts with an agreement, the contract. Before you start green grading you ask yourself: does the coffee in front of me match the contract? That’s the question you want to answer when you green grade coffee.
The first step is to know what needs to be analyzed. Because every coffee origin, supplier, and vendor can use different grading protocols. Unfortunately, the coffee industry does not offer one standard. So, before you decide to green grade, adapt your protocol to the contract.
Having everything in hands reach enables you to put your entire focus on the beans without leaving the table during a session.
Make sure you have a:
Delimit the time you green grade. If you take too much time you will have the chance of green staring: simply not seeing defects anymore because you lose concentration. Our Q Graders set a timer for 20 minutes to green grade one sample at a time.
The sample size depends on your green grading protocol and contract. Check the size of your sample before grading. For example, the SCA advises a sample of 350 grams of beans for a thorough and sound analysis. Other protocols steer to 300 grams.
Now the bulk of the work starts. Carefully scan the sample and spot possible coffee defects. Once you find a defect, pick it from the main pile and put it aside in a separate defect pile.
In our 2-minute video tutorial, you see Cerianne, one of our Q Graders, nip off a sliver from the main pile. She analyses the pre-selection and picks out the coffee defects. This method helps you to break down the green grading in small bite sizes.
Need an overview of all coffee defects? Download our defect poster for free here.
After you’ve analyzed the whole sample, you check the defects and classify them according to the protocol you’re using. Every protocol attributes more or less weight to certain defects. The SCA, for instance, distinguishes primary and secondary defects.
Most green grading systems use an equivalency system. This means you need a certain number of defective beans to count as 1 full defect. E.g. the SCA classifies 5 broken/chipped/cut beans in your sample as 1 full defect. But you only need 1 sour bean to count as 1 full defect. During this step, you determine the weight of each defect.
Now you add up the defects and determine if the sample is in or out of specification based on the protocol you’re using. Grab the contract and compare it to your analysis.
While sifting through the sample, you can notice inconsistencies in the screen size. Some beans are larger or smaller than others. When in doubt about the size uniformity, screen size!
Use your sieve to weigh out 100 grams of the sample. Drop the beans in the upper sieve, which is screen size 20, and shake until you don’t hear any beans falling. Weigh the coffee per sieve. Now ask yourself, is the screen size as it should be?
Green grading protocols often specify the acceptable screen size margins of each grade. For grade-1 coffees, a maximum of 5% above or below the contracted screen size is allowed.
Quakers are unripe beans and they harm the quality of the cup. Once roasted, these unripe beans bring notes of dry paper and peanut to the table, nothing you want in your coffee. The problem with quakers is that you can’t see them with the naked eye while green grading.
To discover these, you need to roast and spot the lighter and underdeveloped beans from the pile. So roast a sample before or after to complete your green grading analysis. Then, add the number of quakers to the form if the protocol requires these.
We’re not scientists, but we can try to break down water activity in plain simple language.
When you measure water activity, you want to find out if the beans offer room for microorganisms to develop and harm the quality of the cup. If there’s too much activity, chances are that bacteria can produce molds, even those that contain dangerous mycotoxins and ochratoxins – read more about these hazards here.
On a scale of 0 (dry) to 1.0 (pure water), you want the water activity of the sample to be below 0.70aw. If the coffee strays above this number, it’s likely cup quality will suffer. Too high water activity can even pose health risks. So, by all means, check the water activity!
Now you stick your nose in, or close-by, the entire sample for a quick check. Does the unroasted coffee smell clean or unclean? Note this down.
What color are the beans? If you see an array of uneven colors within the sample, this might be an indication of bad drying in origin. The colors of coffee beans can differ from blue, blue-green, green, greenish, yellow-green, pale-yellow, and yellowish-brown. Note down the color on your form.
Only one step remains: deciding what to do with the coffee. If the sample matches the contract, you can approve. But if it’s a mismatch, simply reject.
And now you’re done. You understand the basics of green grading coffee: from specifying the contract to making a decision based on your green grade coffee analysis. Besides cupping, the process of green grading tells you if the coffee sample you’ve requested matches the contract.
Underneath, we have listed several industry links that expand on the green grading subject and more:
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