Quakers are coffee beans that do not turn dark brown when roasted. In order for coffee to be considered a special quality, Specialty Coffee Associations require it not to contain quakers.
They don't quite agree on zero tolerance as a green coffee standard, as research has shown that quakers can still appear in coffee even after it's farm and dry mill sorted. We believe a quaker shouldn't necessarily make coffee green. Ultimately, it is the quality of the cup that should determine whether a coffee is their specialty.
But it makes sense to weed out imperfections after your coffee has been roasted.
To understand how we get quakers, we'll start by explaining why good coffee beans turn dark brown.
Inside each coffee bean is an endosperm, which contains a honeycomb-like structure that stores different chemical compounds to nourish the bean, such as sugars and amino acids. According to scientific research led by Mariane Helena Sances Rabelo, coffee beans have to go through seventeen different chemical changes to obtain these compounds.
These chemical compounds are important because when exposed to heat they undergo the Millard reaction and caramelize, thus creating the dark brown color of coffee beans.
Although we do not add sugar to the bean, it is the caramel smell of roasted beans that informs our brain that coffee is sweet. Instead, heat contributes to converting sugars into volatile aromatic compounds (VOCs). VOC has a big impact on how we perceive food (Shepherd, 2012).
Unfortunately, this smell or taste can be impaired if something unusual happens to compounds in a coffee bean's endosperm. When a bean cannot caramelize because its sugars are spoiled, it is called a quaker.
Rabelo's research noted that lighter quakers with higher agtron counts (between 82 and 95) had a statistically significant effect on the flavor of the coffee. Thus, it shows that the aroma of coffee depends on the presence of sugars that caramelize and thicken the bean.
Here are four different ways sugar bean can be compromised:
immaturity
INSUFFICIENT NUTRIENTS FROM WOOD
INSECT ATTACK
MICROBIAL ATTACK
The Arabica Green Coffee Defect Handbook defines quakers as "immature, immature beans." However, more recent research has shown that quakers can also be caused by microbial or insects that compromise a coffee bean's chemical compounds.
Immature beans or beans that are deficient in nutrients often result in "dope quakers." These quakers will cloud the taste of your coffee and result in a less than perfect cup, but they're not the worst flavor you can come across.
Some people claim to prefer tame quakers in their coffees, as excessive fermentation can produce positive fruity notes. It should be noted that there is no empirical evidence to suggest that Quakers can have a positive effect on flavors.
However, Sovda did some applied research and found that over-fermenting normal ripe coffee beans and losing sugar to microorganisms doesn't always have a dire result.
Sometimes these microbes produce esters classified as VOCs with flavors of strawberry and blueberry.
Rabelo's research highlighted that a few quakers in a cup of coffee may have an effect on the coffee's cup score, but four or more immature beans will have a statistically significant effect. According to his research, quakers, astringency and lack of sweetness affect coffee flavor properties.
Sometimes facilities even have a pulper that separates small, immature beans before they are washed. But sometimes the beans are also crumbled or cut in the dough maker, thus damaging the beans and the sugars in the beans.
The last type of defective beans that will affect the taste of your coffee are over-roasted beans and under-roasted beans. Over-roasted beans are usually caused by the beans accidentally going through the roaster twice or getting stuck on the faceplate or another part of the roaster that is hot.
Over-roasted beans cause a smoky or bitter taste.
Under-roasted beans are also usually the result of the beans getting stuck somewhere in the roaster, but in cold machine sections such as the hopper.
Under-roasted beans are very unpredictable and can taste anything from grainy to extremely acidic.
Producing the perfect batch of coffee may seem impossible without Quakers. As noted earlier, Rabelo's research shows that even after on-farm and dry-mill sorting, quakers can still appear in coffee after roasting.
Sovda tells coffee people that quakers are undercooked and overcooked. That's why it exists to offer color grading technology that will eliminate the defects caused by bruises.
These machines use technology that lets you enter what type of beans are/are not wanted. The main criterion is the desired color spectrum for the roasted beans.
After entering a certain profile into the software, the optical sensor will distinguish the bad beans from the good ones and remove the bad beans with a targeted burst of air.