If you've tasted a coffee described as creamy, smooth, or yoghurt-like — with a softness in the acidity and a rounded texture that sits differently from a standard washed — there's a reasonable chance you were drinking something that went through lactic fermentation.
It's one of the more interesting developments in specialty coffee processing over the last decade. And it's something we're actively working with at Jack Murat. This article explains what lactic fermentation is, how it works, and why it produces the results it does.
A quick primer on fermentation in coffee
Every coffee undergoes some form of fermentation between picking and drying. When a cherry is harvested, it begins to break down. Microorganisms — bacteria, yeasts, and fungi — consume the sugars in the fruit's mucilage layer and produce metabolic by-products. Those by-products — acids, esters, alcohols — diffuse into the bean and influence how it tastes in the cup.
For most of coffee's history, this fermentation was uncontrolled. The microbial community that developed depended on what was in the environment — the ambient bacteria on the farm, in the water, in the air. Results varied. Now, producers who want specific outcomes are intervening deliberately: controlling the environment, the duration, and in some cases the specific microbes present. Lactic fermentation is one approach to that controlled intervention.
What lactic fermentation actually means
Lactic fermentation is a metabolic process in which lactic acid bacteria (LAB) convert sugars — primarily glucose and fructose in the coffee mucilage — into lactic acid. LAB are some of the most widely distributed microorganisms in food fermentation: they're responsible for the sourness in yoghurt, the tang in sourdough, the acidity in kimchi and sauerkraut.
In coffee, they occur naturally. They're part of the ambient microbial community on most farms. What changes with a deliberate lactic process is that conditions are managed to favour LAB activity over other microbes — particularly acetic acid bacteria, which produce the sharper, more pungent acidity associated with acetate, and yeasts, which tend to produce fruity, alcohol-forward profiles.
How we create the conditions for lactic fermentation
LAB thrive in low-oxygen, slightly acidic environments with controlled temperature. To encourage them over other microbial populations, we use a variation of anaerobic processing:
• Depulped or whole cherries are placed into sealed, low-oxygen vessels immediately after harvest
• The environment becomes anaerobic quickly as the existing microbes consume available oxygen
• Temperature is managed — typically at or below 20°C — to slow the process and prevent unwanted microbial activity
• Duration is monitored closely, with the fermentation assessed daily for aroma and pH
Under these conditions, LAB outcompete other microorganisms and lactic acid becomes the dominant metabolic output. The result is a fermentation that is slower, more controlled, and more predictable than open-air processing.
In some protocols, a starter culture of specific LAB strains is added to further guide the fermentation. We are trialling this approach on selected lots at Jack Murat — adding known, beneficial LAB strains to provide greater consistency from batch to batch. The results are still being evaluated.
What it does to the cup
Lactic acid has a softer, rounder character than acetic acid (vinegar) or malic acid (the sharp acidity in green apple). In the cup, a coffee that has undergone lactic fermentation tends to show:
• A creamy, smooth mouthfeel — often described as dairy-like or velvety
• Soft, rounded acidity — present but gentle, without the sharp edges of a conventional washed
• Flavour notes often described as yoghurt, cream, stone fruit, or milk chocolate
• Sweetness that lingers through the finish
These characteristics make lactic-processed coffees particularly compelling as espresso and in milk — the softness integrates well with the texture of steamed milk, and the sweetness amplifies rather than competing with it.
How lactic fermentation differs from anaerobic and washed processing
Washed
In a standard washed process, fermentation happens in open or semi-open tanks before pulping or after. The microbial community is mixed — LAB, yeasts, and acetic acid bacteria all contribute. The result is typically clean and bright, with fruit acidity and clarity. It's less directionally fermented than a lactic process.
Anaerobic
Anaerobic fermentation — sealed vessels, low oxygen — is the broader category of which lactic fermentation is a specific type. Not all anaerobic fermentations are lactic: depending on temperature, duration, and starting microbial community, yeast activity may dominate instead, producing more tropical fruit character and higher ester compounds. Lactic fermentation is an anaerobic process specifically managed to favour LAB.
Natural
Natural processing involves drying the whole cherry, with fermentation happening slowly inside the fruit. The result is typically heavier in body and fruit sweetness. Lactic fermentation can technically occur in natural processing, but it's harder to control and the final cup profile is usually dominated by fruit sugars rather than the cleaner, dairy-like lactic character.
What we're doing at Jack Murat
We introduced lactic fermentation to our processing programme in the 2024 season and expanded it in 2025. Our lactic lots are all washed-style: cherries are depulped, then fermented in sealed vessels at controlled temperatures before washing and drying.
The results in the cup have been consistently soft and sweet — the creamy texture and rounded acidity are reliably present across batches. Cup scores for our lactic lots have placed consistently above 83 points in internal cuppings.
We're currently evaluating LAB starter cultures for selected lots, working to understand whether inoculation produces more consistency than relying on the ambient microbial population. Early results are encouraging. We'll report what we find.
Why it matters
The development of controlled fermentation methods like lactic processing represents a meaningful shift in what coffee producers can achieve. For decades, the dominant variables in coffee quality were terroir, varietal, and basic processing method. Now, controlled fermentation adds a fourth dimension — one that can be tuned to specific flavour outcomes without waiting for better growing conditions or new plant genetics.
For Australian coffee specifically, this is interesting. Our terroir produces a clean, sweet base — stone fruit, cane sugar, smooth finish. Lactic fermentation amplifies those qualities rather than overriding them. The creaminess sits on top of what the Catuai already does well. The combination is quietly very good.
If you want to try it for yourself, look for our current lactic lots in the Batch Series.
