“Resting” coffee after roasting is a hot topic, and apparently a confusing one at that. Around the time the Loring became popular and more third-wave roasters began roasting ultra-light, or “Nordic style” it became common for roasters to recommend resting beans for weeks or months after roasting. That was a revolutionary change from traditional practices.

Why we rest coffee for espresso

Historically, most roasters and baristas were on the same page when it came to resting beans to be pulled as espresso. Pulling shots of coffee roasted recently and ground on demand results in massive amounts of crema and lower extractions than shots pulled from beans several weeks off roast. The reason for this is likely that the back pressure caused by degassing during espresso extraction forces the barista to use a coarser grind with very fresh coffee, and/or the outgassing may make it more difficult for the water to rapidly dissolve solids from intact cells within the grounds. (In a pressurized espresso basket, there is nowhere for the gas to escape to; in filter brewing, gas released when water wets the grounds escapes into the atmosphere, and does not provide meaningful back pressure.)

Until the last several years, common practice was to rest espresso beans, but not beans for filter coffee. More recently, especially as the popularity of the Loring has exploded and the more roasters have chosen to roast ultra-light, resting has become a standard, almost universal practice. 

Why would we rest beans for filter coffee? 

There seems to be a connection between the strength of beans’ cellulose structure and the need to rest coffee. Lighter roasts have stronger, less brittle, less porous cell structures. I am not sure if anyone knows exactly what changes during resting, whether the cellulose weakens with time or (more likely) some chemical changes occur slowly to affect coffee flavor in a way that makes the coffee seem more developed. Most of us would agree that the lighter the roast, the more resting is required to reach the coffee’s flavor peak. 

What factors make resting beneficial?

As noted, light roasts seem to benefit more from resting. Coffee from air roasters seem to benefit more than coffee from drum roasters. Presumably, the conductive heat transfer in drum roasters damages the outer layers of the beans during roasting, weakening the cell structures, and making them more porous, more developed, and less in need of resting. 

Resting times among different air roasters

I have spent the last several months roasting on two air roasters, a Roest sample roaster, and a 15kg IMF. I roast on the light side by almost any standard, and my roasts seem to benefit from some rest. However, while they may peak one or two weeks after roasting (the jury is still out), they taste perfectly fine a day or two after roasting. 

But not all air roasters are the same; in my experience, coffee from Loring machines requires longer resting periods than coffee from other air roasters. I’m not sure why that is, but one of two unique features of Lorings is the likely culprit: the roasting chamber is pressurized, and the roasting environment is oxygen-free (I cannot confirm that, but Loring claims that is the case.) One of those two factors is likely the reason why coffee from Lorings needs longer resting times than coffee from other machines. 

How long should you rest coffee? 

Judging by my inbox, many people assume all roasted coffee needs lengthy resting periods. Of course, everyone has his or her own preference. But I would argue optimal roasting time depends on roast level, whether the coffee came from a drum or air roaster, and if from an air roaster, whether the machine was a Loring.

If I were forced to drink a dark, oily roast, I would not rest the coffee for more than a day, as the coffee will likely taste a little rancid within a few days. (And of course I would add salt, haha.) I don’t find coffee from classic-drum roasters benefits from more than a day or two of rest, unless the coffee is what I would consider underdeveloped. As for air roasters, I would probably rest the coffee from one to four weeks, depending on development level and whether the coffee came from a Loring. 

Storage conditions and resting

While not usually a part of the resting conversation, how roasted coffee is stored affects quality after a given resting period. At one extreme, freezing vacuum-sealed beans slows the aging process so much that it would probably take months or years to reach the same condition as coffee rested for a week or two at room temperature. Likewise, pressurized cans, such as those used by Illy, can slow the aging process to a crawl. Beans stored in cooler conditions will evolve more slowly, while beans stored in warm environments will degrade much faster.

The bottom line

There is no one size fits all resting period. Consider the type of machine, roast and development level, and storage conditions when trying to guess when a coffee will peak. Comments welcome.