Slight skunk smell

[namballe]

i'm getting a very slight skunky type smell from my roasted beans. it seems to occur when the beans are 10 or more days post roast. whenever i open the bag to grind the beans, i can smell the slight skunky smell filling the air. other than that, the coffee is good. anyone else have an experience like this? wonder if it's a bad thing or a good thing:?:

 

[PinkRose]

Has this happened with more than one batch of roasted beans?

A few weeks ago, I bought roasted beans, the same kind that I always get. They had a slight skunky, burnt-rubber type of smell, which was very noticeable every time I opened the bag. It's very hard to describe what it smelled like. When I first smelled it, I thought it smelled like "cat pee," but after a few seconds, it seemed more like a burnt rubber smell (which is kinda similar to skunk).

The coffee tasted fine, but it was unusual that the beans had an such an off odor. It wasn't obnoxious, but it was noticeable.

The new beans that I bought last week don't have that smell.

I hope one of our roasting professionals knows what may have happened to the beans to make them smell so strange.

Rose

 

[JumpinJakJava]

Greg, hope this helps.

"The basis of coffee aroma is sulfurous compounds. These include strong smelling mercaptans (skunk smell is an example) or onion, garlic, and even sweet, honey-like aromas. All sulfur compounds are highly susceptible to oxidation in the presence of oxygen. Some of these compounds, those that have toast, bread, or roasted-meat aromas, are relatively stable, but others change quite rapidly."

You could read the whole article here, especially under the section:
Coffee Aroma: A Complex Balance of Diverse Compounds

A Question of Freshness | Black Bear Coffee

Also was wondering if the bag/container you keep the fresh roasted coffee in has old coffee oils in it. Old coffee oil becomes rancid.
I am continually wiping out containers with paper towels.

I found this also:
My coffee smells like tuna fish

Interesting comments here ("The compound with the closest description is probably methanethiol, which leaves a “putrid, cabbage like” sense impression.")

 

[John P]

Without knowing what beans, and what their grade is, I would say:

The likely culprits.

1) It's just bad coffee full of defects.

1a) Or it's a herbal odor you have a hard time describing, prevalent in many Sumatran coffees... even excellent Northern Sumatran offerings.

If #1 is not true, then it is

2) Over roasted/ roasted improperly.

At ten days, it's not going to organically degrade to give bad odors.

Is this a recent thing or has it always happened?
Does it happen with every bean you use or just a specific one?

 

[namballe]

Also was wondering if the bag/container you keep the fresh roasted coffee in has old coffee oils in it. Old coffee oil becomes rancid.
I am continually wiping out containers with paper towels.

JJJ,
you hit the nail on the head! i am reusing old valved bags to save a few cents. (only for my consumption). thank you all very much