Double Anaerobic Coffee: What It Is and How to Brew It
Double anaerobic coffee is coffee that went through two fermentation stages, with at least one of them in a sealed, low-oxygen tank, before it was washed and dried. There is no single standard recipe. Producers differ on timing, temperature and whether the mucilage stays on the seeds, so the cup can range from dense and syrupy to loud and funky. This guide explains what happens in the tank, how lactic fermentation fits in, what to look for on a bag, and how to adjust your brewing so the coffee tastes sweet instead of sharp.
TL;DR
- Double anaerobic (also called double fermentation) means two fermentation stages, usually whole cherries first, then depulped coffee in a sealed tank. Exact methods vary by producer.
- Lactic fermentation is a related idea: it encourages lactic acid bacteria, usually inside an anaerobic tank, and it is not a synonym for “double.”
- Expect intense fruit, sweetness and body. Vinegar, solvent or rotten-fruit notes are signs of a fermentation that went too far.
- A good bag or lot sheet tells you what was fermented, for how long, and how it was dried.
- At home, brew a little cooler, use a stronger ratio, and add 10 to 20% bypass water if the cup is too intense.
Table of Contents
- What double anaerobic coffee actually means
- How the process works, step by step
- Lactic fermentation, lactic process and lactic anaerobic: how they relate
- Natural anaerobic vs. double anaerobic
- What it tastes like, and what it should not taste like
- How to tell a genuine double anaerobic coffee before you buy
- Brewing double anaerobic coffee at home
- Our perspective on fermented coffee
- Get fresh single origins delivered
- FAQ
- Sources
What double anaerobic coffee actually means
Two words are doing the work here. “Anaerobic” refers to fermentation without oxygen, normally in a sealed tank. One importer’s overview notes that the term broadly means using a sealed tank and does not specify whether the coffee is whole cherry or depulped, or how it is processed afterward. So “anaerobic” on its own tells you very little.
“Double” means the coffee ferments in two stages. The same overview describes multi-stage fermentation as covering different sequences, such as whole-cherry fermentation followed by parchment fermentation, and says some coffees made this way are called double fermented. A magazine explainer on double fermentation adds that it can also mean a whole-cherry pre-ferment followed by depulping and a second fermentation, or a post-fermentation water soak.
That is why you will see “double anaerobic,” “double fermentation” and “double washed anaerobic” used for lots that are not identical. Treat the phrase as a family of methods, not a fixed specification.
How the process works, step by step
Because there is no standard, the clearest way to understand it is to read one real example. A documented dual-fermentation lot from Finca El Encino in Mexico followed this sequence:
- Whole cherries were fermented in bags for 60 hours.
- The cherries were depulped.
- The depulped coffee was fermented anaerobically in its mucilage, in tanks, for 12 hours.
- The coffee was washed.
- It was dried on raised mesh beds for about ten days.
The first stage starts breaking down the fruit sugars while the cherry is still intact. The second stage, in a sealed tank, pushes the fermentation in a more controlled direction. Washing and slow drying then lock in the result.
Other producers run it differently. A coffee dictionary entry points out that there is no standard duration or temperature, and that accounts disagree on whether mucilage remains during the second fermentation. If you read two descriptions of “double anaerobic” that do not match, that is normal.
What producers can control in either stage is time, temperature, pH and sometimes inoculation with added cultures, according to the same importer overview. Small changes in those variables shift the cup a lot, which is why two double anaerobic coffees from neighboring farms can taste nothing alike. If you want the producer’s side of the tank in more depth, our piece on controlling anaerobic fermentation covers the 24 to 72 hour range.
Lactic fermentation, lactic process and lactic anaerobic: how they relate
Readers often search for double fermentation and lactic fermentation together, and the terms do overlap. They describe different things, though.
Perfect Daily Grind defines lactic fermentation as a type of anaerobic fermentation in which lactic acid bacteria convert simple carbohydrates into lactic acid. Carbon dioxide, ethanol and sometimes acetic acid can also form. The same article reports two approaches specialty producers use to encourage it: inoculating with a selected lactic-acid-bacteria starter, or using a 2 to 3% salt brine in a low-oxygen environment.
For the producer, a magazine guide to lactic processed coffee explains that the aim is to create conditions that favor Lactobacillus cultures. That means fermenting sugary cherries in an anaerobic tank and monitoring pH, temperature and oxygen.
In plain terms:
- Lactic process coffee and lactic anaerobic coffee both point to a fermentation steered toward lactic acid bacteria. Producers and sellers use the words loosely, so check the lot description.
- Double anaerobic coffee describes the number of stages, not the microbes.
- A coffee can be both: a two-stage ferment whose tank stage is managed to favor lactic bacteria. A sheet that says so will usually spell it out.
Sellers do not use these labels consistently, so the process description matters more than the label.
Natural anaerobic vs. double anaerobic
A natural anaerobic coffee is usually understood as whole cherries sealed in a tank to ferment without oxygen, then dried with the fruit still on, as in a classic natural. Since the term anaerobic doesn’t specify whether the coffee is whole cherry or depulped, the “natural” in the name is what tells you the cherry stayed intact through drying.
The differences you can expect at the cup:
| Natural anaerobic | Double anaerobic | |
|---|---|---|
| Stages | Typically one sealed stage | Two fermentation stages |
| Fruit during drying | Dried as whole cherry | Usually washed, then dried as parchment |
| Common impression | Heavy fruit, jammy, winey | Dense, sweet, often more structured |
| Clarity | Can be heavy and fermenty | Often cleaner, though still intense |
The table describes typical patterns, not rules. Washed double anaerobic lots can still be wild, and a carefully run natural anaerobic can be delicate. If you like to compare processing styles side by side, our flavor guide to coffee processing shows where each fits.
What it tastes like, and what it should not taste like
Fermentation builds flavor, and it can also overshoot. Here is the range.
The good version. Dense body, ripe fruit, brown sugar sweetness, sometimes a long chocolate finish. A producer-minded study in Peru, published in Coffee Science, scored anaerobic processing at 87.38 against 84.00 for washed and 85.75 for natural under its sensory protocol. The same study found anaerobic and natural processing had lower physical yields than washed and honey methods, which helps explain why these coffees cost more.
The risky version. One importer notes that anaerobic coffees can have over-the-top fruitiness and artificial sweetness, and that the method can produce varied and unpredictable flavors. A green coffee profile lists over-fermentation warning signs: vinegar or excessive acidity, solvent-like or overly alcoholic notes, and rotten-fruit, onion or dirty flavors.
If you taste the second list, the coffee was either pushed too far or brewed in a way that exaggerates the funk. The second problem is one you can fix in your kitchen.
How to tell a genuine double anaerobic coffee before you buy
Because the label is loose, look for a description of the process rather than the word alone. A trustworthy bag or lot sheet answers these questions:
- What went into each stage? Whole cherries or depulped coffee?
- Was the mucilage left on during the sealed stage?
- How long did each stage last, and was temperature recorded?
- How was it dried? Raised beds, patio or mechanical, and for how many days?
- Was anything added? Starter cultures, brine, fruit or flavorings.
As one importer puts it, a lot sheet should state what was fermented and how it was dried. If you see only “double anaerobic” and a list of tasting notes like candy and cocktail, you are working with marketing language, not process information. Specificity, such as the 60-hour and 12-hour stages in the Mexican lot above, is the signal of a producer who tracks the work.
Also check the roast. Heavily dark roasting buries fermentation character, and very light roasting can leave it sharp unless the coffee is rested and brewed carefully. Ultra-light roasting works when the green coffee is clean and the brew is dialed in.
Brewing double anaerobic coffee at home
Intensity here is partly a concentration decision. A brew test on a Colombian anaerobic lot found that higher total dissolved solids emphasized processing flavors, while more water gave a mellower, more transparent cup. That lot included an adjunct, so it is not a pure double anaerobic example, but the lesson carries over.
Start with a cooler brew
One brewing guide suggests starting around 200°F (93°C) rather than 205°F (96°C) for extended-fermentation coffees, because higher temperatures can emphasize sharp, vinegary notes. It also recommends a stronger ratio and expects shorter drawdowns.
Dilute with bypass
If the cup is still too much, the same guide recommends diluting it with 10 to 20% bypass water. Brew a slightly strong coffee, then add hot water to the carafe or mug. Our guide to bypass in pour over walks through the math. A brewer like this one gives you a lot of control over the final strength without changing the extraction.
A reference recipe
For a washed anaerobic lot from Guatemala, Fellow’s published recipe uses:
- 20 g coffee
- 315 g water at 205°F
- a 50 g bloom for 45 seconds
- a total brew time of 3:00 to 4:00
It reports tasting notes of guava, milk chocolate, rich body and nougat. Note that this recipe sits above the 200°F starting point, so treat it as a benchmark and adjust. If the coffee tastes sharp, drop the temperature. If it tastes thin, tighten the ratio.
Quick fixes by symptom
| What you taste | What to try |
|---|---|
| Vinegar, sharp acidity | Lower the water temperature toward 200°F, shorten contact time |
| Boozy, heavy, too intense | Add 10 to 20% bypass, or use more water in the recipe |
| Flat, muted | Raise the dose, grind slightly finer, use fresher coffee |
| Funky and unpleasant even when diluted | Try a different lot; the fermentation may have run too far |
Brew these coffees near their peak, within the first few weeks after roasting. For the basic technique, our pour over guide covers grind, pours and timing, and our piece on how brewing method shapes flavor helps if you are choosing between filter and espresso. Espresso drinkers can try the approach in blooming espresso for a more filter-like sweetness.
If you want to taste how a clean washed profile compares before judging a heavily fermented one, brew a straightforward bag first. You can buy specialty coffee beans from other origins and varieties for that kind of side-by-side, or revisit our washed process tips. Water matters too: our coffee water recipes show how mineral content changes sweetness and acidity. For a different long-ferment style, read about carbonic maceration coffee.
Our perspective on fermented coffee
We roast ultra-light, in the Nordic tradition, because we want the coffee itself to speak: the origin, the variety, the farm’s decisions. Processing is one of those decisions, and fermentation is the most expressive of them.
Our view is that a fermented coffee deserves the same respect as any other single origin. That means knowing how it was made, roasting it so the character is preserved, and shipping it fresh so you taste it at its best. We ship on the day of roast for exactly that reason.
What we also believe is that your palate is the best guide. Some people love a bold, fruit-forward cup, others prefer clarity. That is why our subscriptions are built around your feedback: tell us what you liked, and your selections move toward it. Brewing tweaks like lower temperature and bypass water let you tune any coffee to your taste, and we publish guides so you can do it with confidence.
Sean
Get fresh single origins delivered
If you want to explore processing styles at home, our subscriptions bring ultra-light, Nordic-style single-origin coffees to your door, roasted to order and shipped the day they are roasted. You give feedback on every bag, and your selection adapts to your taste. Browse the options on our subscription plans page, or send a bag to a fellow coffee lover with a gift subscription.
Curious about limited releases? Our Tasting Series is where we feature special coffees for people who like to compare.
FAQ
Is double anaerobic coffee the same as double fermentation coffee?
In everyday use, yes. Both describe coffee that ferments in two stages, with at least one sealed, low-oxygen stage. The details differ by producer: some start with whole cherries and then ferment depulped coffee, others add a water soak. Check the lot description for the actual sequence.
Is lactic fermentation the same as anaerobic fermentation?
Not exactly. Lactic fermentation is a type of anaerobic fermentation in which lactic acid bacteria convert sugars into lactic acid. Anaerobic fermentation is the broader term for any fermentation without oxygen, so a lactic coffee is anaerobic, but not every anaerobic coffee is lactic.
Why does my anaerobic coffee taste like vinegar or alcohol?
That can come from the fermentation itself or from your brew. Vinegar, solvent and alcohol notes are listed among over-fermentation warning signs, but hot water can also exaggerate sharpness. Try about 200°F (93°C), a stronger ratio, and 10 to 20% bypass water before concluding the coffee is the problem.
Does double anaerobic coffee have more caffeine?
Nothing in the research we reviewed links fermentation style to caffeine content, so we would not assume it does. The amount in your cup depends mainly on how much coffee you use and how you brew it. Dose and ratio are the levers you control.
What is a natural anaerobic coffee?
It is generally a coffee fermented in a sealed tank as whole cherries and dried with the fruit on, like a natural. A double anaerobic coffee, by contrast, goes through two fermentation stages and is often washed before drying.
Sources
- Understanding Coffee Fermentation From Classic to Experimental
- Finca El Encino lot
- Double Anaerobic (Coffee Processing)
- Understanding the Process: Double Fermentation
- Lactic fermentation: What roasters need to know
- Know Your Methods: Lactic Processed Coffee
- Effect of processing methods on Peru Catimor, Coffee Science
- Anaerobic coffee: what it is and how to specify a green lot
- Five Tips for Brewing Anaerobic Coffees
- Crown Jewel Colombia Circasia Edwin Noreña
- Brew recipe for Guatemala Cuevitas Anaerobic
