The question that appears time-after-time in my inbox is appropriately about time itself: when does coffee go bad? I have addressed this query a couple times indirectly (here & here) but given the repeated requests, let’s go deep for this dispatch and explore roast dates, degassing, staling, best-before’s and all things aging.
Roasting is a seemingly simple process: we apply heat to foster chemical changes that make green beans into brew-able brown beans. However, it is in the variation of time and temperature that complexity arises: amino acids and reducing sugars generate Maillard reactions and Strecker degradations; volatile compounds form and vanish; cellulose walls strain and fracture. By the time beans drop into the cooling tray, the final flavours of the cup are locked into place.
While there are now over 1000 volatile compounds identified in coffee, it is only a small segment that are responsible for a coffee’s taste profile. There are studies (Caporasoa, et al.) that connect such compounds to our sensory experiences (for example, hexanal is “green, grassy” or ethylpyrazine is “nutty, peanut, butter” or ethyl propanoate is “sweet, rum, juicy”). Given that coffee is a living organic product, we might presume that drinking it as soon as possible would be the key to experiencing compounds responsible for the “caramellic” or the “fruity”.
However, there is an issue because roasting renders beans porous and then traps residual gases (mostly CO2) in all these little gaps and spaces. If we want to brew very fresh coffee, the gases clash with water, inhibiting the ability to evenly move those flavour volatiles from grounds to cup. Fun side note: according to studies, this collision is what forms both the crema and the bloom (Smrke, et al). While the majority of these gases disperse within a couple days, there is lingering build-up. The tail end of this process can take months, which explains why we needs valves to prevent exploding bags (Baggenstoss, et al.). To draw upon my barista days, espresso was always so much easier to dial-in when it was at least two-weeks off-roast and at the cupping table time was always on my side for the fruity, bright, and complex notes.
My suggestion for resting times, like many others, comes by way of anecdotal evidence. If you drink coffee daily, you likely have a strong opinion on best practices. And yet, the issue is assuming that coffee is a constant while rest time is a variable; like so:
X * Y = Z
COFFEE * TIME = FLAVOUR
In these conversations, we lock in ‘coffee’ and then just vary ‘time’ until we reach the ‘flavour’ we seek. And I suppose such an approach is possible with dark roasts, since you no longer taste the always-changing or perennially-unique aspects of origin. Instead, the sensory experience reflects the roaster itself, in all its burnt and chard intensity. Moreover, such destruction means larger craters and weakened walls in that porous structure, so gas exits quickly. Plus, according to multiple studies, those oily lipids exposed by darker roasts are susceptible to oxidation (Taci, et al) and prone to going rancid (Budryn, et al.) Thus, because we have very little variation in flavour, we can say:
DARK ROAST * SHORT TIME = DELICIOUS
DARK ROAST * LONG TIME = GROSS
With much ease, this formula explains the long standing and deeply entrenched fresh-is-best logic for coffee. Drink it fast as it is quickly losing flavours and going rancid.
And yet, all these varied studies disrupt this myth by arguing that roast degrees directly impact degassing rates. To quote Wang and Lim’s study, “the roasting temperature-time conditions determines the residual CO2 content after roasting, as well as the subsequent mass transport phenomena occurred during storage”. It then follows, our X is no longer stable. Coffee is not singular but rather a shifting and fluctuating object, dependent on a huge swath of factors like country of origin, varietal, processing, fermentation drying, and so on. Consequently, Y is up for grabs!
The question is then: how not fresh is best? Some of these studies suggest medium roasts take about 33 days to dispatch 90% of the residual CO2 while others put the marker further at 75 days. This is not necessarily the best window however, as while CO2 is leaving (and/or degrading) so are those flavour volatiles. In one particularly detailed exploration, the authors chart how specific aromatics disperse at incongruent rates (Marin et al.). Meaning for example, 2-methylfuran and 2-butanone, which are associated with pungent fruity and buttery notes, peak at the one-month mark and do not drop significantly until the five-month mark. While those green and grassy hexanal compounds dissipate in a couple weeks. Thus, drinking after two weeks but before two months might provide the best profile for that coffee to both avoid vegetal flavours and experience peak fruit deliciousness.
The take away here is that such a timeframe or window is ideal for that particular coffee. So, its best before (and after) date is inexorably tied to the very individual and specific qualities imparted by origin and the roasting process. This answer is a tad clunky compared to the slicker and compact ‘fresh is best’ mantra. I can however provide some general guidelines specific to Quietly and those light to medium roasts generally.
The dense interlocking structure of light roasts remain intact compared to those more fragmented and patchy dark roasts. To make a seasonal analogy, light roast sits robust with yellow and crimson foliage beside all those barren and leafless dark roasts. So, while the wind might readily take away all of a dark’s roasts CO2 and potential flavour volatiles with ease, it will take much more time to work its way through a light roasts’ leaves. So always wait at least 10-14 days to ensure water can reach, saturate, and pull away all those compounds that make a coffee taste like ripe fruit, juicy berries or sweet caramelized sugars. On the other end, if you are going to drink a coffee within 90 days, it will be fine without an artic trip to the fridge or any carbonite encasing. So, to the formulas:
LIGHT ROAST * 14-90 DAYS = DELICIOUS
LIGHT ROAST * LESS THAN 14 DAYS = GROSS
LIGHT ROAST * MORE THAN 90 DAYS = SEAL & FREEZE
DARK ROAST * MORE THAN 14 DAYS = GROSS
DARK ROAST * LESS THAN 14 DAYS = GOOD(ISH)
In terms of storage, heat and water will start the extraction process so treat your bag of coffee like potatoes or gremlins. Do not pre-ground because that essentially zeroes the timeline with all CO2, flavour volatiles, and aromatics dispersing within minutes. To extend the analogy, you’ve chopped and mulched the tree.
The funny aside to the argument that we should ‘not take coffee as the constant’ is that we often take time as persistent and unchanging in character. I mean granted its always present, continual, and unending. But my lived experience suggests its quality, like the variance in roast degrees and ensuing cup profiles, has a more unique and shifting feel. On one of my grad school nights of pints, my pal Amy pointed out how there are endless modifiers (adjectives, compound nouns, adverbs and otherwise) for the word time: travel time, ill-timed, running time, naturally timed, time zones, wasted time, work time, time limit, go-time, lead time, rest time, hard times, ancient times, spare time, real time and so on.
This year of living in a pandemic feels like perpetual waiting time. Holding off seeing people or doing things means we exist within a suspension or pause. I cannot help but feel a weird echo with every email suggestion to “rest your coffee” because we are all in that weird purgatory waiting to brew, to start, to act, to go. I wanted to end this dispatch with one of my favourite Don DeLillo quotes from his book the Body Artist but it is not on the shelf. I must have loaned it to a friend and I am, appropriately, waiting to get it back from them – whenever I see them again. The quote, for what it is worth is, “time is the only narrative that matters”. And more than ever, cups of coffee and life included, it seems relevant – maybe even timeless.
Trust the Process,
Baggenstoss, Juerg et al. “Influence of Water Quench Cooling on Degassing and Aroma Stability of Roasted Coffee”. Journal of Agricultural and Food Chemistry. 55, 16 (2007): 6685-6691.
Budryn, Grażyna et al. “Influence of roasting conditions on fatty acids and oxidative changes of Robusta coffee oil” . European Journal of Lipid Science and Technology. 114 (2012): 1052-1061.
Caporaso, Nicola et al. “Variability of single bean coffee volatile compounds of Arabica and robusta roasted coffees analysed by SPME-GC-MS”. Food Research International. 108 (2018): 628–640.
Marin, Krešimir et al. “A New Aroma Index to Determine the Aroma Quality of Roasted and Ground Coffee During Storage”. Food Technology and Biotechnology. 46, 4 (2008): 442-447.
Smrke, Samo et al. “Time-Resolved Gravimetric Method To Assess Degassing of Roasted Coffee.” Journal of agricultural and food chemistry. 66 21 (2018): 5293-5300.
Toci, Aline. “Changes in triacylglycerols and free fatty acids composition during storage of roasted coffee”. LWT – Food Science and Technology. 50, 2 (2013): 581-590.
Wang, Xiuju and Loong-Tak Lim. “Effect of roasting conditions on carbon dioxide degassing behavior in coffee”. Food Research International. 69 (2015): 144–151