2 September 2026 · 5 min read
over the last decade a wave of «experimental» processing has swept specialty coffee. lots appeared with flavours that once seemed impossible: bubblegum, lychee, rum, strawberry wine, melon. behind most of them sits one word — fermentation, only run on purpose and pushed to extremes. it's the most discussed and most controversial topic in coffee today.
what fermentation actually is
fermentation isn't «spoilage» or chemistry in a bad sense. it's the natural work of microbes (yeasts and bacteria) feeding on the sugars in the cherry's mucilage and giving off acids, alcohols and aromatic ester compounds. in classic processing (washed, natural) it happens on its own and briefly. experimental methods take it under tight control: time, temperature, acidity (pH), oxygen access, and sometimes even specific yeast strains added on purpose.
anaerobic fermentation (without oxygen)
the cherries — whole or already de-pulped — go into sealed steel tanks and the oxygen is pushed out, often by pumping in carbon dioxide. without oxygen, different microbes work than in open air, and the flavour shifts: more complex esters, a «jammy», compote quality, winey and boozy notes, a denser, almost syrupy body. the process runs from a day to several, under constant pH and temperature control — the processor is basically turning winemaker.
carbonic maceration
the term comes straight from winemaking (it's how beaujolais nouveau is made). the whole cherry ferments in a co2 environment under pressure, and part of the transformation happens inside the intact fruit rather than outside it. the result is very bright, almost «neon» fruit notes that are hard to mistake. it's the riskiest and most spectacular of the methods: a small error and the miracle turns to vinegar.
thermal shock and other tricks
after fermentation a lot may be rinsed sharply, first with hot then with ice-cold water (thermal shock), to lock in the profile and stop the microbes with a sudden temperature swing. there's also inoculation with specific (say, wine) yeasts, extended fermentation over 100+ hours, and fermentation with controlled oxygen access at certain stages. each trick adds its own shade.
the ethical grey zone
«infused» coffees stand apart — maceration with added fruit, spice or flavourings. when chunks of passionfruit or cinnamon go into the tank, that's NOT coffee processing but flavouring, even if the bag stays modestly quiet about it. a good processor tells you exactly what they did; if the taste is suspiciously identical to a flavouring and there's no hint of the variety, be wary.
where the quality line runs
good experimental processing AMPLIFIES and complicates what's already in the bean. bad processing drowns the origin and makes every lot taste the same: «the same fermentation» instead of «the same region». red flags: a taste identical to an artificial flavouring; a total loss of the variety's character; a sharp «boozy» or vinegary edge tipping into a defect. a quality anaerobic stays clean and balanced — just with a far wider palette than the classics.
how to brew these lots
experimental lots are dessert, not everyday coffee, and they usually cost more. brew them as filter, a little coarser and cooler (88–92°c) than usual, so you don't over-extract an already powerful, concentrated profile. let the cup cool — the full fruity complexity opens up when it's warm. and drink it attentively, in small sips: the fun here is tracing just how much a single bean can hold.
in short
anaerobic and carbonic aren't «marketing for its own sake» but a real technological leap that widened our idea of what coffee can be. the key is to tell masterful processing that reveals the bean from a trick that hides it under an artificial taste. try them, compare them to a classic from the same region — and your own palate will quickly learn to tell one from the other.