When does coffee go off? If I've ground a batch of coffee, I know I should use it as soon as possible, but if I store it (in an opaque, air-tight, slightly-below-room-temp container), how long have I got to use it? Are there any key points at which the quality will degrade (e.g. after a day, after a week)?
Whole Bean Coffee Degradation Over Time

Whole bean coffee will go stale within 14 days - on average. The graph below shows the quick 1.5 standard deviation drop in quality within the first 14 days (marked in red). *See note below for details



Staling in the context of coffee has a commonly agreed on definition - the loss of volatile aromatic compounds and the oxidation of surface oils on the roasted coffee beans. The loss of aromatics affects the flavor profile because: 1) they are both part of the same degradation process and 2) the majority of what you taste in coffee is flavors from volatile aromatics through retronasal olfactory sensation.

This graph was created using data from Analytical Flavor Systems where we build quality control and flavor profiling tools for craft beverage producers. Perceived Quality is a non-hedonic assessment of a product's quality. This time series is taken from a degradation study.  

Ground coffee, on the other hand, will stale within minutes. 70 cc of ambient air is enough to render one pound of coffee stale. On average, this process takes seven minutes. 

Interestingly, the degradation curve looks about the same! 



Data Analysis Minutia (notes)

This time series model was segmented using daily Perceived Quality means from a random selection of 15,000 coffee reviews. All coffees included are whole bean, freshly ground, third wave coffee brewed in a Chemex with a bleached filter. 

Certain other brewing methods, particularly methods optimized for older coffee such a Nel, may show a different degradation curve. 

The staling point was selected by a parametric statistical change point analysis, which searches for shifts in the mean and variance of a time series. This time series was modeled for change point analysis using a Poisson distribution as  we're searching for the average number of coffees that go stale within a specific time-point, and the model was set to find at most one change.