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Potatoes, Leaf Rust, and other coffee tidbits

2013 April 12
by Ryan

Okay all, time to put your ed-you-mah-kay-shun hats on for this post. I have some things I want to talk about…

First up, let’s talk potato. In coffee. Ugh, right?

In a few east African countries like Burundi and Rwanda a defect can creep through all the processing of the coffee bean. Only once the coffees are roasted and ground can this defect show up. The aroma in the room will change from the lovely coffee aroma to one of raw potato peels bordering on old, wet potato. Yuck.

How this defect occurs in nature is still somewhat a mystery, but research is pointing towards a bacterial infection of the coffee cherry while it is still on the tree. The bacteria is airborne, too, which makes it even harder to pin down. While the bacteria is present worldwide, it seems to be concentrated in the east African countries. Once the bacteria enters the coffee cherry, it starts eating into the beans and turns that stellar cup into one of yuck.

It really comes down to the growers being super-vigilant about picking and processing only the coffee cherries that aren’t showing any signs of issues. But even the most eagle-eyed picker will slip here and there. And once it’s processed, you can not tell when a bean will “throw” that defect.

Does this kill that entire bag of coffee sitting on that counter? No. Just that one batch you just ground. Can it kill your preference towards that particular coffee? Of course.

I bring this up simply because of the fact that we have found some of the potato defect in the Rwanda we had and the Burundi we now carry. All we ask (and all we can do, really) is please try to grind and brew another cup if you get handed a defective cup. If the pound continually throws the defect, please bring it back in and we’ll replace it–no questions asked.

More information on the potato defect can be found at:


So lets move from current coffee issues to future coffee issues.

As you know, coffee is a natural, organic product. Being such, viruses and diseases can and do affect crops. The latest crop issue is Leaf Rust.

The Leaf Rust Disease in all its glory

The Leaf Rust Disease in all its glory

This disease, officially called Hemileia vastatrix , has run rampant in Central America this year. Guatemala is looking at a 30% reduction in their crops, while Costa Rica is looking at upwards of a 40% loss. Honduras, Mexico, and Peru are not free from this either.

The Leaf Rust disease attacks the leaves of otherwise healthy arabica coffee trees. As stated in the article by the Specialty Coffee Association of America,

It is no secret that climate changes are already being felt by coffee growers in Central America and throughout the world. Changes in both temperature and rainfall likely contributed to this unusual outbreak. Warming temperatures at higher altitudes and the resulting shifts in moisture accumulation are likely allowing the rust to thrive in areas previously uninhabitable (Avelino et al. 2006). The case of leaf rust is an example of how changing patterns of, rather than the total annual amount of precipitation, can really alter an ecosystem. Disruptions in the typical dry season can create an environment more habitable for rust outbreaks. Smaller and more frequent rainfall in the region likely contributed to the perfect fungal habitat.

There are other factors that may have exacerbated this particular outbreak. Some are convinced that the changes in land use and coffee farming practices is the primary reason for recent outbreaks. They believe that the shift to high density monoculture allows the easier transmission of rust. What is really going on? We do not have all the facts. The exact perfect storm for a massive multi-country severe rust outbreak is currently an unfortunate puzzle. The truth is that since there is not a full understanding of the biology of this fungus it is impossible to understand what exactly could affect its growth and proliferation, let alone how to eradicate it. This seems to be another example of where the scientific research on coffee is sadly lagging behind that of other crops.

Long story short: it’s going to take some serious research in how to prevent this from becoming even bigger of an issue than it already is, and there’s no real organic control of the disease yet.

I don’t know what will happen to pricing on our Central American coffees at this point, but I have a strange feeling it isn’t going to be pretty. I’ll keep you updated…


And now for something completely different…

I have been promising that our workshops will be starting up again now that we’re settled in to our new digs, and I am not lying. I will be scheduling the events this weekend, so keep an eye on our events page for the latest information. The one thing I am sure of is that our weekly coffee cuppings will happen on Thursdays at 4:00pm weekly starting next week. Otherwise, be on the lookout for Coffee 101, Advanced Brew Methods, and Home Roasting Basics workshops!

Thanks for reading all this: there’s a lot of interesting things happening in our little world of coffee right now!


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