Anaerobic, Carbonic, and the Fermentation Years

Coffee grows as a small red fruit, about the size of a cranberry, with the seeds inside. Those seeds are what you grind. Getting them out of the fruit and dried is called processing, and it turns out to change the taste enormously — the same seeds handled two different ways make two different drinks.

For about a century there were basically two ways to do it. Wash the fruit off straight away and dry the clean seeds, which gives you a bright, clear cup. Or dry the whole fruit with the seeds still inside, which gives you something heavier and jammier. The trade calls those washed and natural, and we wrote about them in 2013.

Then, while we were asleep, somebody started sealing the fruit in tanks.

What “anaerobic” means on a bag

Anaerobic just means “without air.” The fruit goes into a sealed tank instead of an open one. As it sits there it gives off carbon dioxide, which pushes the oxygen out, and once the oxygen has gone a different set of microbes takes over the job of breaking the fruit down — the ones that can work without air.

Different microbes, different byproducts, different flavors. The cup comes out very sweet, heavy on fruit, with a boozy or winey edge and a thick, syrupy feel in the mouth. It’s the same idea as the difference between a fruit left in a bowl and one sealed in a jar, except somebody is doing it on purpose and charging for the result.

One thing that confuses everybody, reasonably: anaerobic describes only that one sealed step. The producer still has to dry the coffee afterward, and can do that any of the usual ways. So a bag can honestly say both “anaerobic” and “natural.”

And carbonic maceration

Borrowed wholesale from winemaking, where it’s how Beaujolais is made. Same sealed tank, except instead of waiting for the fruit to push the oxygen out, carbon dioxide is pumped in to drive it out deliberately. One to three days later the coffee comes out and gets dried.

The results are floral and fruity in a way that simply doesn’t happen otherwise. The first time you meet a good one it’s genuinely startling — people put the cup down and look at it.

Our actual opinion

The best of these are extraordinary and we wouldn’t want to live without them.

The problem is the middle of the field. A lot of this coffee tastes overwhelmingly of the processand not much of the coffee — strawberry, cinnamon and a faintly alarming cider note, in roughly that order, regardless of where the bean actually grew. When the processing is the loudest thing in the cup, the place it came from has been buried, and the place is supposed to be the point.

There’s a version of this that is essentially flavoring, done far enough upstream that the label doesn’t have to admit it. There is also a version that is the most exciting thing to happen to coffee in twenty years. Both sit on the same shelf and the bag rarely tells you which you’re holding.

Our rule, for what it’s worth: buy the experimental lot from a roaster whose ordinary coffee you already trust. If they can make a clean, straightforward cup sing, the fermentation is a decision. If they can’t, it’s a costume.

And keep drinking the plain stuff. It went briefly unfashionable while all this was happening, which is the best possible moment to buy anything.

For where this sits among everything else going on at the moment, here’s the short version.