The Science Behind Experimental Fermentation
Modern coffee processing has evolved far beyond traditional methods, with producers leveraging advanced microbiology to manipulate fermentation environments. During coffee processing, lactic acid bacteria (LAB) from multiple ecosystems (water, native soil, air, and plant) find in the cherry pulp a rich environment for their development. They utilize pulp substrate as a source of carbon and nitrogen to produce significant amounts of lactic acid. This natural fermentation is purposely used by coffee growers to promote an efficient removal of the mucilage layer adhering to the fruits, before storage and transport of the coffee beans.
Lactic and acetic acids were the main acids produced during fermentation. The precise control of these acid productions forms the foundation of experimental processing techniques. During fermentation, LAB consumes the carbohydrates present in the coffee pulp—such as glucose and fructose, and other molecules from the breaking of pectin, such as arabinose and galacturonic acid, amino acids, free fatty acids, citric acid, and others—and produces different metabolites, such as lactic acid, and organic volatile compounds, such as 2,3 butanediol, acetic acid, ethanol, and other esters. Besides lactic acid, LAB metabolism produces a variety of compounds from the utilization of citrate and the catabolism of amino acids. Recent studies have demonstrated that these metabolites have a complementary function in the formation of taste and flavor precursors of coffee beverages.
Lactic Fermentation: Creating Creamy Complexity
Essentially, it’s a type of anaerobic fermentation, which means no oxygen is present during the process. The dominant microorganisms are Lactic Acid Bacteria (LAB), which thrive in oxygen-free environments. LAB converts simple carbohydrates into lactic acid – as well as carbon dioxide, ethanol, and sometimes acetic acid.
Lactic fermentation is a processing process that allows anaerobic lactic acid bacteria such as Leuconostoc mesenteroides inherent on the beans to quickly produce and metabolize sugars in the mucus, creating lactic acid. One of these methods is lactic fermentation: a process championed by the innovative La Palma y El Tucán in Colombia.
Producers employ two primary methods for inducing lactic fermentation. Currently, manufacturers often use two main lactic fermentation methods in specialty coffee: LAB starter vaccination and using 2-3% brine. These two methods are performed in a low-oxygen environment under strict control to promote healthy LAB growth. According to coffee experts, fermentation using 2% salt water is the optimal way to create a delicious and attractive cup of coffee. Because LAB is salt tolerant or halophilic, it grows and develops in high salinity conditions and easily enhances the flavor of the seeds.
Lactic fermentation allows for the growth of lactic acid bacteria under anaerobic conditions with constant measurement of oxygen level, sugar content, and pH. The bacteria feed on sugar present in the mucilage, generating a high concentration of lactic acid. After reaching the desired pH, the coffee is soaked in clean water to stop the growth of bacteria and dried on raised beds.
This usually results in a creamier mouthfeel, as well as more yoghurt-like flavours.
According to a recent study, lactic fermentation using LAB can give coffee a floral, fruity, creamy, buttery flavor. They can also produce a deeper sweetness with chocolate notes and a smooth taste.
Acetic Fermentation: Harnessing Oxygen for Brightness
Acetic fermentation represents the opposite approach to lactic processing, embracing aerobic conditions to generate acetic acid. La Palma’s acetic fermentation is similar to what’s often called a “dry fermentation.” After depulping, the coffee is placed in concrete tanks, but instead of being soaked in water, it’s regularly stirred. The presence of oxygen leads to an increased amount of acetic acid—an acid normally associated with natural process coffees.
Unlike anaerobic fermentation, acetic fermentation involves aerobic environments where oxygen interacts with the fermentation process. Natural Yeasts and Bacteria – Wild microbes, including Acetobacter, promote the conversion of alcohols into acetic acid. Temperature Control – Warmer fermentation temperatures (25–35°C) accelerate acetic acid production.
A significant shift was observed in the proportion of AAB, particularly in the semi-anaerobic fermentations, where they made up between 20% and 57% under these conditions.
Our acetic processing aims to encourage a low to medium bodied coffee with a wine to citrus like acidity, and a very sweet aftertaste.
Coffees that undergo this process tend to have a sharp, complex brightness. Think of: Red fruit notes like cherry, cranberry, and pomegranate; Wine-like characteristics with earthy undertones; Sparkling acidity that carries through the finish.
The balance between beneficial acetic acid production and over-fermentation requires precise control. This treatment also showed increased lactic acid (8.76 g/Kg) and reduced acetic acid (6.40 g/Kg). The Conventional process presented a higher acetic acid content (10.12 g/Kg).
Too much exposure and the coffee becomes sour and unpleasant. But with skilled handling, the result is a vibrant, tangy cup that dances on the tongue.
Thermal Shock: Temperature as Processing Tool
Thermal shock processing represents one of the most dramatic innovations in experimental coffee processing. First very hot, then very cold - the thermal shock process is true coffee alchemy and at the same time a revolutionary approach to coffee processing. Invented by Alex Bermudez from Finca El Paraiso, it is an innovative trend that gives coffee farmers and growers opportunities to experiment and coffee lovers new ways to enjoy coffee. Quite simply, the previously cleaned and de-pulped coffee beans are exposed to extreme temperature fluctuations during processing.
Thermal shock typically occurs at the end of fermentation, during a stage when the coffee is heated in its own juices to temperatures between 104°F and 122°F. This heat causes the coffee’s pores to expand, allowing the seeds to absorb more of the juice’s aromatic esters. The coffee is then rinsed with cold water—around 50°F—which causes the pores to contract and “lock in” those absorbed compounds.
They are first heated to 30 to 60 degrees and then cooled, sometimes even to -50 to -80 degrees. This is possible using dry ice, liquid nitrogen or other methods. As a rule, however, the coffee at Finca El Paraiso is first washed with water heated to 40 to 45 degrees Celsius and then cooled to 4 degrees Celsius.
The method emerged from unexpected inspiration. “A dream in which I heated coffee with hot water,” says Alex Bermudez. “And then dipping it in a container of cold ice.” He then told his brother Diego about the dream. He used pans from his mother’s kitchen and immersed the coffee first in hot water and then in cold water. Without telling anyone, he roasted the coffee and placed it on a cupping table. “Wow, what’s that?” asked his brother Diego. It was the best coffee on the table.
Implementation and Quality Control
Modern experimental processing requires sophisticated monitoring throughout fermentation. A team of experts thoroughly monitors and analyzes the events in the bioreactor during the entire fermentation period. It measures pH, temperature, carbon dioxide and alcohol levels as well as the number of all possible bacteria. Fermentation needs to be turned off at exactly the right moment.
All this work done in the field of wine fermentation has led to experimentation with thermal shock, after which it is possible to carry out coffee fermentation at low temperatures with the inoculation of selected microbial strains. This avoids the formation of acetic acid and favors the formation of desirable flavor and aroma precursors that are not formed during a conventional fermentation process.
In the case of coffee it is very important to preserve the viability of the seed embryo after the thermal shock. Therefore, the time of exposure to heat and the temperature of the water are variables that each producer must adjust, always bearing in mind that a scalding time of 3 minutes with boiling water causes the death of the coffee seed embryo.
As mentioned earlier, using the thermoshock method can greatly enhance the coffee’s sweetness and overall organoleptic properties. Alongside sweetness, the bean sealing phase of the thermoshock method also traps delicious aroma compounds into the coffee, which only become released upon brewing. The precision required for these processes has led to This treatment was the only one classified as specialty coffee (score 85.00). The inoculation of S. cerevisiae using the SIAF method proved effective in enhancing the quality of wet coffee, producing consistent and high-quality beverages that meet specialty coffee standards.
Future of Experimental Processing
These experimental methods represent a paradigm shift in coffee production, moving from traditional fermentation to engineered flavor development. It takes plenty of dedication, knowledge, and time to carry out lactic fermentation to the highest standards. But Felipe and Christopher both believe these processing methods are some of the most reliable and economical ways to change coffee flavour and mouthfeel. When done right, there are clear advantages to implementing such techniques.
The integration of thermal shock with controlled fermentation creates unprecedented possibilities. This process involves painstaking cherry selection and cleaning, fermentation in a low-oxygen environment, selected yeast and bacteria culture creation, isolated and inoculated cherry juices, a marriage of components, and a finished thermal shock. The resulting coffees have pronounced acidity and intense, fruity flavors. As producers develop their understanding of microbial management and temperature manipulation, these techniques will likely evolve from experimental curiosities to standard tools in the pursuit of exceptional coffee quality.