Quakers and Taste – 2020 Sensory Summit

Feb. 24, 2020

Coffee is science, and we have the studies to prove it! 

This year, two Sweet Maria’s team members had the chance to attend the Sensory Summit at UC Davis. Organized by the Coffee Roasters Guild with support from the Specialty Coffee Association (SCA), this event allows folk like us from the coffee industry to connect with the scientists behind the most cutting-edge research in the coffee world. After two days of smelling and tasting, and lots of statistical jargon, we walked away with a boatload of new knowledge and the objective data to back it up. 

Now, we want to share everything we learned with you! Keep an eye out over the next few weeks for new blog posts, demos and tasting events – our first event in the series covers basic sensory evaluation of coffee and will be held on Wednesday, 3/18  . To reserve a spot, send an email to [email protected]


Quakers in Coffee

One of the most illuminating lectures of the weekend concerned quakers. Quakers are immature beans that have a higher concentration of amino acids and lower concentration of sugar. They are resistant to roasting; a quaker does not have the chemical compounds to have a proper browning reaction in the roaster (Maillard reaction, caramelization) and as a result will remain pale in color. Quakers are associated with unpleasant bitterness and astringency, or the flavor of burned popcorn. 

A pale quaker bean (right) stands in stark contrast to a typical roasted coffee bean (left).

So how noticeable are quakers? Mariane Rabelo, a PhD student at the Federal University of Lavras in Brazil, decided to find out. Quakers are a particular issue in Brazil for a few reasons;  Brazil is one of the only places where coffee is harvested and sorted mechanically rather than by hand, which can lead to a higher percentage of unripe beans. The popularity of dry processing in Brazil also leaves these coffees vulnerable to quakers, which are more prevalent in dry process coffees. Why are dry process coffees more likely to have quakers? Unripe cherries float in water, so it’s easier to remove cherries that contain quakers during channel grading in wet processing. Wet process coffees also go through a depulping machine that can remove unripe cherry

Rabelo assembled a panel of trained quality graders and had them cup several samples of the same coffee with an increasing percentage of quakers. She also broke quakers into three categories based on color: classic, brownish yellowish, and brownish. Amazingly, the brownish quakers had no significant effect on the sensory attributes of the coffee at any threshold. The brownish yellowish and classic quakers did lead to perceptible increases in astringency and bitterness, as well as decreases in sweetness and acidity, but these effects were not noticeable until quakers constituted ~9% of the beans in the sample. That means the probability of perception is actually surprisingly low! 

Given the high concentration of quakers necessary for off-flavors to be noticeable in the cup, is it worth taking the time to sort out quakers after roasting? Timothy Hill, now a trader with Atlantic Specialty Coffee, used an optical color sorter to find out. Hill sorted the quakers out of both washed and natural coffees and had folks taste each version of the coffees, sorted and unsorted. In this test, surprisingly, there was no preference for the sorted vs. unsorted coffees.  Turns out, Hill’s existing profiles had already factored in the presence of quakers with regard to the desired final product. Before he could see a perceptible preference for the sorted coffee, Hill had to reverse engineer his profiles for the quaker-free coffee. 

Our takeaway at Sweet Maria’s? Don’t stress out over quakers in your cup. We always list the the defect count under “Appearance” in our coffee reviews and our coffees fall well below the perceptible threshold for quakers – that includes Sumatras, which often have a more varied appearance. Our cupping notes take into account whatever small percentage of defects or quakers may be present. If you still want to sort through your coffee after roasting, go for it – but sorting probably won’t make a huge difference in the final product. 

To drive this home, we tried our own experiment. We brewed three pots of Kenya with an increasing number of quakers had our staff give each brew a taste.

We brewed three pots of Kenya with an increasing number of quakers in each batch.

You might wonder why we used a high grown Kenya rather than a Brazil. We initially tried to use a Brazilian coffee, but there were too few quakers in the coffee to generate a high enough percentage for the experiment! We were only able to extract a high enough number of quakers from the Kenya because we had roasted well over 100 lbs of this coffee for our roasted coffee subscription.

All of the quakers from a full day of production roasting – for reference, we only noticed ~3 quakers per pound.

In our (very loosely constructed) trial, we found that even the pot with about 10% quakers tasted good. There are a few reasons why quakers might make less of an impact in a Kenya compared to a Brazil – the higher scores in sweetness and acidity, for one, can mask some of the off-flavors associated with quakers. As the cup cooled, the quaker flavor became more pronounced – even so, a surprisingly quaffable brew!

Ryan and Julio lead a discussion about quakers with the Sweet Maria’s staff.

Based in part on lectures by Tim Hill (Atlantic Specialty Coffee) and Mariane Rabelo (Federal University of Lavras)

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