Potato Defect (also known as Potato Taste Defect, or PTD) occurs in coffees from Rwanda, Western Uganda, Burundi, and the Democratic Republic of Congo. It smells and tastes exactly like raw potatoes, as the name implies.

What Is Potato Taste Defect?

Potato Taste Defect (PTD) is caused by a naturally occurring chemical called 2-isopropyl 3-methoxy pyrazine (IPMP). This compound is present in trace amounts in all coffee beans and in some other foods, most notably grapes, where it can occasionally impart an earthy flavor to wine. In certain coffee beans, IPMP is present at much higher concentrations, producing an aroma and taste reminiscent of raw potato.

The reasons why IPMP is more concentrated in some beans and confined to coffees from Rwanda, Burundi, Western Uganda, and the Democratic Republic of Congo remain unclear. Researchers have studied this defect since the 1950s, but no definitive answer has been found. Although the aroma can be detected from the farm soil through the green and roasted coffee, there is currently no scalable method for identifying and removing affected beans.

The word defect is scary! In coffee, “defect” simply means an irregularity that keeps the coffee from tasting its best or staying fresh as long as it should. PTD is considered a flavor defect: harmless to consume, but divisive in its sensory profile. Some might even enjoy the earthy notes. At Counter Culture, however, we don’t consider it part of an ideal coffee experience. 

Luckily, PTD is relatively rare and easy to avoid. The exceptional qualities of coffees from these regions far outweigh the risk of encountering a tainted cup. Mitigating the risk is easy and worth it. We’ll explain how below:

Identifying Potato Taste Defect

Unlike other defects, PTD has no known visual indicators. Affected beans can only be identified through smell or taste. Ideally, you will smell it so you never have to taste it! Here’s our recommended protocol to minimize the chance of brewing PTD-affected coffee:

• Smell before brewing

  • Always smell the ground coffee from these regions before brewing.

• Grind in small batches

  • Grind your coffee in small amounts. For home brewing, we recommend grinding <30 grams at a time. For batch brewing, we recommend grinding 100 grams at a time.

• Evaluate the aroma

  • If you only smell delicious coffee, continue brewing and enjoying these incredible coffees!

  • If you think you might be smelling potato, your brain might be telling you it is there because you learned about PTD. It’s probably not! Check out our Taster’s Flavor Wheel to see what else you might be smelling.

  • If you do smell raw potato, you’ll know! Trust us. Compost what you just ground. 

• If PTD is present

  • Purge the grinder of any remaining chaff/fines

  • If possible, grind through a bit of coffee that is guaranteed not to have PTD (such as Colombian coffee) to prevent transfer to the next batch of coffee.

  • Repeat step 1

How Prevalent Is Potato Taste Defect?

There are widespread misconceptions about the risk and prevalence of PTD, and many industry decisions are based on limited data. We conducted research* to help the specialty coffee community adopt more informed, realistic expectations. 

In our research tracking PTD in dozens of coffees over several years, we’ve found that it occurs at an average rate of 1 affected bean per 3.3 pounds of coffee. In whole-bean form, PTD does not transfer between beans. If you open a bag and detect a potato-like smell, it’s likely coming from a single bean. The odds of encountering more than one PTD bean in a 12-oz bag are pretty low, though there is always some element of randomness—that is just the nature of the beast.

*We conducted a statistical analysis to determine how much coffee needed to be evaluated to predict PTD presence accurately. Our findings show that a sample size of 5,600 grams (just over 12 pounds) achieves 90% confidence in a coffee’s PTD incidence rate.

To validate our methodology, we partnered with chemists at Seattle University. We submitted both defective and non-defective coffee beans, which they analyzed using a sniffing machine that detects elevated levels of IPMP. Their results aligned perfectly with our evaluations, confirming the accuracy of our detection process.

Why Buy These Coffees?

At Counter Culture Coffee, we purchase coffees from PTD-affected regions because, aside from this infrequent defect, they are among the world's most dynamic coffees. We believe the producers behind them deserve access to markets that value their quality and the care they put into producing them.

We remain hopeful that a long-term solution to the root (forgive the pun) problem will be found. In the meantime, we hope this information empowers you to brew confidently and appreciate these coffees' remarkable quality.