Is it that simple for your green coffee? Is it possible that over time, something changes, and your coffee can lose it's flavor even before it is roasted?
The answer is surprisingly complex. In fact, to what level could depend completely on the coffee itself and the original flavors present. There is most definitely no catch all answer. Some coffees may show this "agey" flavor change whereas others may not show perceivable age. The important part in analyzing this is roasting in a way that you can perceive a difference. The one thing that is certain is that 'something' is changing whether we can perceive it or not.
Chemical and structural changes happen over time in storage that have been well documented. Temperature, humidity, and light seem be the things that can expedite those changes. It should be a given that exposure to chemical agents, molds, and other contaminants should be avoided but these can also contribute to biodegradability.
George Howell has pointed to lignins previously as proof of the biodegradability of coffee seeds. Lignin is a biodegradable plant material that is hydrophobic. This means it is water resistant and resists pathogens entering or possibly flavors escaping while acting like a glue binding the seed together. Coffee seeds are very waxy, so it really brings up the question of how hydroscopic the coffee is in the green state and what part that plays into the flavor changes. Lignins are only about 2% of the total coffee mass so it remains to be seen if this 'glue' is the sole culprit in bean decomposition or plays a part along with volatile flavor components that may escape over time.
What is truly curious is the relationship between sugars and how flavors form as well as the overwhelming topic of moisture content. Sugars are increasingly interesting according to the research on low molecular weight sugars in green and roasted coffee collected in Ivon Flament's 'Coffee Flavor Chemistry
.' Poor storage was believed to result in an increase of glucose which correlated with a marked increase in woody/rubbery notes in the coffee. There was also an increase in water content during the same period, so it remains that moisture content of the bean is an easier measure of green quality than a quantitative sugar analysis. Storage in tropical temperatures (such as at origin) can even induce chemical changes such as the Maillard reaction in the green coffee.So what does that tell you food scientists?
There are changes in coffee in the time it is stored that need to be addressed by expedited shipping, better storage method, and possibly freezing green.
Is that conclusive proof that we should all start flying coffee from origin and freezing green? No. What it points to is that we need to set up conditions where we can do a qualitative analysis of the changes coffees in storage go through and continue pursuing the upgrades you see from pioneers like Daterra Farm in bagging.
From a recent experiment we did with a CoE quality green stored in air conditioned storage and one frozen over the last year, we had a very stark contrast in the two. The differences we have noted are that floral citrus notes in wp centrals, wp Yirgs, and clean Kenyas appear to disappear over time to be replaced with a woodsy dull lifeless note and an unpleasant wheat or barley flavor. Aromatics disappear first, followed by changes in the citrus notes. Naturals turn quickly from the soft over ripe fruit into very muddy rotten fruit flavors over time in storage. We don't have enough notes on controlled dry process to state definitively what is changing.
Those are just our evaluations and this is a challenge to roasters to make their own evaluations and share their observations. Keep in mind that if the green quality isn't already very high, you may not notice the changes. This is not something to invest in your Sumatra at $1/lb but might make sense for that $20/lb CoE Guatemala.
Point being, if you paid a lot for this coffee, you should research keeping it in it's best shape as long as possible whether you are a professional roaster or the home variety.
