Lactic processing manages fermentation so that lactic acid bacteria dominate rather than yeasts — the same organisms responsible for yoghurt, sauerkraut and sourdough.
How it is done
By restricting oxygen and controlling temperature, producers create conditions where lactic bacteria outcompete other microbes. Sometimes cultures are added directly.
The fermentation typically runs long and cool.
The result
A distinctive creamy, dairy-like sweetness — yoghurt, condensed milk, sometimes a savoury edge — alongside intense tropical fruit.
It is genuinely different from anaerobic or carbonic processing, and recognisable once you have tasted a few.
Why it works
Lactic acid is softer and rounder on the palate than the acetic acid that dominates uncontrolled fermentation. Shifting the microbial balance shifts the acid profile, and with it the whole character of the cup.
The risk
Poorly controlled, lactic fermentation goes sour and vinegary like any other. The precision required is why these lots are expensive.
Where it comes from
Colombia and Costa Rica principally, with the technique spreading quickly.
Brewing it
Filter, very light roast. The creaminess also shows well in an immersion brewer.