Here’s a guide to co-fermented coffees! What they are, how they’re made, and why transparency matters.

Co-fermented coffees are some of the most talked-about coffees in specialty right now, and also some of the most misunderstood.

From intensely aromatic fruit-forward profiles to subtle floral or spice-driven expressions, co-fermentation raises important questions:

– What does co-fermented actually mean?
– How is it different from infused or flavoured coffee?
– What role do fruits, yeasts, bacteria, botanicals or even syrups really play?
– And where should transparency sit in all of this?

We wrote about this topic a while ago (you can read that here), and things have changed a lot since then!

As we release new co-fermented coffees produced by the Bayter brothers at El Vergel Estate in Colombia (and one coffee from a partner they work closely with, Huver Castillo), this article aims to clearly explain the different techniques used in co-fermentation, without hype or judgement!

What does ‘co-fermented’ mean?

At its core, co-fermentation means that something is intentionally introduced during fermentation to influence microbial activity and flavour development.

This addition can be:

• Fruit or fruit pulp
• Fruit juice or must
• Cordials or syrups
• Selected yeast or bacterial cultures
• Botanicals or spices

The defining factor is timing: the addition happens during fermentation, while microbial activity is taking place.

This is fundamentally different from flavoured coffees, where aromatics are applied after processing.

On the other hand, infused coffee means there is a 1:1 flavour transfer between the substance added and the end result, almost entirely bypassing the microbial reaction.

Co-fermentation exists on a spectrum

Not all co-fermented coffees are made the same way. Techniques range from microbiologically driven to flavour-directed, and understanding this spectrum helps explain why these coffees taste so different.

1 / Whole-fruit or pulp co-fermentation

One of the most common methods.

How it works

• Coffee cherries or parchment ferment in tanks
• Fresh fruit, dehydrated fruit or fruit pulp is added
• Natural sugars feed yeasts and bacteria
• Aromatic compounds migrate into the coffee seed

Flavour outcome

• Expressive fruit aromatics
• Juicy acidity
• Often vibrant and immediately recognisable

This method is highly sensitive to fruit quantity, temperature, fermentation time, and oxygen exposure.

2 / Juice or mosto-based co-fermentation

Instead of whole fruit, producers may add:

• Fresh fruit juice
• Mosto (the ‘juice’ from a previous coffee fermentation)
• Fruit reductions

Why it’s used

• More precise sugar availability
• Better consistency
• Lower microbial risk than whole fruit

Flavour outcome

• Cleaner aromatics
• More controlled expression
• Often wine-like or floral rather than jammy

3 / Yeast-led co-fermentation

Here, the driver isn’t the fruit. It’s the microorganism.

How it works

• Selected yeast strains are introduced
• Sometimes paried with an added sugar source
• Yeasts convert sugars into aromatic esters

Flavour outcome

• Enhanced florals
• Tropical or stone-fruit esters
• High sweetness perception with cleaner structure

Yeasts don’t add flavour directly. They transform sugars into aroma compounds.

4 / Bacterial-led co-fermentation

Less common, but increasingly explored.

What’s involved

• Lactic acid bacteria or mixed cultures
• Often anaerobic conditions
• Longer fermentation times

Flavour outcome

• Creamier mouthfeel
• Softer acidity
• Lactic, yoghurt-like or kombucha-style notes.

This approach requires a high level of fermentation control.

5 / Cordials, syrups, and concentrates

An increasingly used and often under-discussed method.

What’s added

• Fruit cordials
• Reduced fruit syrups
• Sugar syrups infused with botanicals
• Fermented fruit concentrates

Why producers use them

• High repeatability
• Precise dosing
• Reduced variability from fruit seasonality
• Lower microbial risk/activity

Flavour outcome

• Clear, defined aromatics
• Consistent intensity
• Can range from subtle enhancement to bold expression

Technically, these coffees are still co-fermented but also would technically qualify as infused, as there is still interaction with microbes, but also a 1:1 flavour transfer.
They sit closer to the flavour-directed end of the spectrum and require clear disclosure.

6 / Botanical or spice co-fermentation

This includes ingrediants such as:

• Cinnamon
• Vanilla
• Herbs
• Flowers

These methods can produce striking results, but also raise important questions around balance, traceability.

Co-fermented vs flavoured coffee (they’re not the same)

This distinction matters!

Co-fermented coffee

• Additions happen during fermentation
• Microbes play a central role
• Flavour develops inside the seed

Flavoured or infused coffee

• Aromatics added after processing
• No fermentation/microbial activiy involvement

Both exist. Only one should be called co-fermented.

Our position at Zest

At Zest Specialty Coffee Roasters, we don’t believe in drawing hard moral lines around processing styles.

We encourage exploration in all its forms: whole fruit, yeasts, bacteria, cordials, syrups, botanicals. As long as:

• The coffee is safe to consume
• The process is intentional
• The technique is clearly disclosed
• The drinker knows what they’re choosing

Co-fermented coffees don’t need defending. They need explaining.
When people understand how a coffee was made, they can decide whether it excites them, challenges them, or simply isn’t for them.

That choice should always belong to the person drinking the cup.