Is it me or the coffee? This question comes up regularly in online groups for home baristas I participate in. Oftentimes members post pictures of “off” looking beans they received, describing taste and asking for feedback.
The word 'defect' comes up quickly in comments to these posts, but not everything is a defect and not all defects are equally bad.
So let’s look at what qualifies as a defect, what causes them and how they can impact the flavor in your cup.
The Two Types of Defects
Green coffee defects happen in the field, during processing, and/or storage before the coffee reaches a roaster.
Field damaged beans can be caused by genetic factors in the plant, pests, diseases, poor soil management, and too much or too little water to name a few. Process damage can happen during harvesting and when coffee goes through the wet or dry mill. Lastly, improper storage conditions can expose green beans to fungus and pests like moths and grain beetles.
The second group is called roast defects. Those are caused at the roasting facility and are tied to the roaster’s skill.
To be clear, no one wants to buy from a roastery that works with defective green beans, no matter how skilled they are at roasting. For completeness however it’s important to add that the impact of defects on your cup varies.
On a Scale of Bad to Worse - Primary and Secondary Defects
I’m sticking to definitions as defined by the SCA here since that is our category of interest. Primary defects are those that will spoil your coffee even in very small quantities. Three examples of this are fungus damaged beans, severely insect damaged beans and what we call full black beans that contain dead tissue and cells which can be due to several of the factors I mention above.
Secondary defects often impact the evenness of a roast, and therefore the taste, but to a much lesser degree and without health implications. Examples of secondary defects are unripe, chipped and parchment containing beans. These often make it into large commercial production. Since they still come 100% from Arabica trees that's what you'll read on the label. While the FDA prohibits the blending of defective lots to hide poor quality, there are no limits on the amount of defects that can be present in a coffee as long as they don't pose a health hazard, and there are no legal requirements for companies to disclose the amount of bean defects to consumers on packaging.
The complete list of green defects is extensive and within each category divided further with scores based on impact. In this article I list the most common examples. If you’d like to dig deeper, check out http://www.coffeeresearch.org/coffee/classification/htm
How Many Defects Can End Up in Your Cup
In specialty coffee zero primary defects are allowed in any batch, and less than five secondary defects per 350 grams of green coffee sample. This is not the only factor that determines quality and the price that the producer can get for their lot, but a large one.
While it is not possible to sample every batch before export, an educated roaster has rigorous quality control in place and should reject any product that doesn’t deliver what the sample promised. That is to say, when you choose to purchase specialty coffee you should never find primary defects in your bag and very few, and better none, of the secondary ones.
Impact On Taste
Primary defects like full Black, fungus and severe insect damage all produce varying degrees of off-flavors and aromas like stinky, moldy, dirty, rubber-like, potato, phenolic (chemical) or highly fermented, along with loss of flavor and body. Granted, ‘highly fermented’ becomes a tricky metric these days with processing that aims for exactly that. However, if it makes you gag and if it is the main flavor in your cup, it’s probably not by design.
Secondary defects can still have a noticeable, often unpleasant effect on taste. The main issue is that these beans roast unevenly and thus cause a flavor imbalance in your cup. Common examples are Elephant (shell) beans and small pieces that were crushed during processing. They over-roast fast and cause bitterness.
The opposite happens with immature beans which are denser and roast slower or barely at all (you would be able to spot those easily as they look different shapes pale and/or waxy). Coffees with immature beans mixed in taste green-ish, grassy, peanut-like and have higher astringency.
If you ever do end up with a green defect in your product, chances are you’ll detect it by taste first, and shape second. Green defects often create a specific mis-shape of the bean, or show a strongly different color (or lack of color) that stands out among other beans in the roasted batch.
Let's move on to the roasters' side of things.
The Not So Magnificent Seven - Roast Defects
Over-roasting:
This is caused by too much heat application over too long a time. Over-roasting results in a bitter, ashy, often astringent taste that lingers. There is little to no acidity nor deep sweetness in the cup. The latter is a great pointer that helps separate a great dark roasted coffee from an over-roasted one. A skilled roaster can create very dark roasts (French, Italian and full City) that have a wonderfully rich chocolate and often burnt caramel sweetness. That kind of lusciousness is completely absent in an ashtray forward over-roasted offer. It’s not super uncommon to see coffees that are labeled dark roasts and are over-roasted. But this is easy to spot by taste and by the excess oil on the beans’ surface that is forced out of the cells during roasting.
Baking (over-development):
Baking can be difficult to differentiate from over-roasting when you first encounter it. In baking, the beginning temperature of the roast was not high enough to trigger the necessary chemical reactions that develop flavor. There is a small window of time when this should happen. As a “fix” the beans are then roasted longer at a high temperature to achieve caramelization. The price for this is that large amounts of aroma compounds simply disintegrate along the way. The taste result is oat- or breadcrust-like, sometimes paper-y. The main difference between a baked and an over-roasted coffee is that baked coffees tend to retain a bit more acidity, whereas an over-roasted one is mostly ashy or flat. But neither one is balanced.
It’s worth mentioning though that baking is sometimes used on purpose to offset the taste of lower quality green coffees for use in espresso and dark roasts that feature a highly 'roasty' profile.
Under-roasting:
The opposite of over-roasting. Too low a heat application over too short of a time. Under-roasting results in grassy, acidic and weak taste and little body. Just like with over-roasting and dark roasts, sometimes you’ll see a bag labeled as light that is actually under. You can tell the difference by looking for balance in your cup.
As a rule of thumb, anything that seems ‘one note’ and lacks body, sweetness
and/or mouthfeel is leaning in the direction of over- or under-roasted. That is after you rule out your own influence over the preparation.
Under-development:
This is often mistaken for an under-roasted coffee, but it offers a helpful visual clue. An under-developed coffee is exposed to high heat in the beginning of the roast which triggers fast chemical reactions, and the roast is then cut short. This results in a pronounced acidity with burnt undertones and a light body. Even though they are similar in taste (minus the burn), under-developed beans look darker than under-roasted ones.
This visual causes a common confusion as you may look at the external color and believe that you have received a medium instead of a light roast, only to find a flavor profile that tastes under-extracted.
To add one more layer, the Nordic roasting style intentionally brushes up to under-development to create bright, mega lively offers. Tim Wendelboe being a master at this. But in the end you can always come back to the essential tell-all: If a cup has no sweetness at all and is lacking in balance, it’s probably not by design.
Scorching (inside/external):
This one is easy to spot. Scorched beans show dark, charred patches, mostly on their flat side. This comes from bumping into the wall of a drum roaster where the initial (charge) temperature was too high.
Scorching can also happen on the inside of the bean if the heat exposure is so sudden that it causes an exothermic reaction so that the inside burns faster than the outside. You would not be able to spot this without cracking the bean open. But taste-wise either form of scorching produces mostly highly smokey flavors.
Tipping:
Tipping is also easy to spot and is a form of scorching, but instead of on the flat side, tipping burn marks appear at the tip of the bean. While it is clearly caused by heat exposure and shows up at the thinnest area of the bean, there are different theories as to when tipping occurs during the roasting process and what else contributes. Taste-wise, tipping often produces cereal-like and ashy flavors. Which can be especially unpleasant in light roasts.
Facing:
The amplified version of scorching. With facing, the flat surface of the bean is charred. One reason for this can be an overloaded roaster in which the beans have no room to move around. As with other defects, facing features burnt and smokey flavor, especially in light roasts.
Non-honorary Mention - Craters:
These are considered defects but are not affecting taste as much. Craters look like little sink holes on the rounded side of the bean (you can see one in the tipping picture above on the same bean). They happen when internal pressure during roasting leads to CO2 literally being pushed out. Craters’ main caveat is that they reduce the shelf life of your coffee as oils are being ejected onto the surface. That oil gets stale and the coffee loses freshness faster.
Summary
The common thread with all roast defects is that they have to do with timing and heat application. If you end up with any defect in your bag it’s likely that you will see more evidence of a roast defect than you will of a green defect because roast defects happen in larger numbers per batch, while green defects can contaminate a whole batch with only a few of bad beans mixed in.
To Keep In Mind
Roasting is not about outside appearance. Coffees can be lighter or darker in color on the inside than they appear externally. So you can’t visually determine the exact roast- and development level for sure until you grind a small sample of the coffee.
I hope this helps. As always, if you have questions, comments or a story idea, get in touch!
PS: Make sure to try our selections of awesome coffee, roasted to perfection, pure and free of any defects and additives.