In recent years, fermentation has been used in coffee to significantly affect the quality of the drink.
Lactic acid fermentation
Lactic fermentation is a microbiological process carried out by Lactobacillus and Enterobacteriaceae bacteria that produces lactic acid from sugar to obtain coffees with a different taste.
pyruvate produced during glycolysis is converted into lactic acid by the enzyme lactate dehydrogenase.
Do you know that lactic acid bacteria produce a large amount of aromatic substances (ketones, esters and aldehydes) that can give coffee fruity, creamy, buttery and floral notes?
Process of lactic acid fermentation
- Growers must be able to create an ideal environment for the growth of Lactobacillus cultures. These are the same bacteria responsible for the formation of lactic acid in milk production.
- During malolactic fermentation, coffee producers must select cherries that are perfectly ripe and have as high a sugar content as possible.
- They then have to place the cherries in an anaerobic environment, e.g. a sealed keg or tank, and then add the Lactobacillus cultures while the coffee is fermenting.
- The farmer has to be very focused during the fermentation process. pH, temperature and available oxygen must be carefully monitored and controlled. This is the only way to create optimal conditions for the lactobacilli so that they thrive and dominate the fermentation.
- After reaching the desired pH level, fermentation is stopped and the beans are steeped in clean water to stop bacterial growth. Then drying takes place as with any other processing method.
Malolactic fermentation can also be used for whole cherries. Therefore, it is quite possible that the term is combined with other processing methods, such as e.g.:
The coffee was lactic acid fermented and dried with the skin and fruit of the cherry still intact.
In this procedure, the skin and fruit are removed beforehand.
What to watch out for in lactic acid fermentation
- Malolactic fermentation is classified as anaerobic because the oxygen has minimal interaction with the cherry and there is no agitation.
- Coffee cherries processed using the lactic acid fermentation method typically have high Brix and pH levels. These conditions help the fermentation process exceed the minimum 80-hour duration required for any lactic acid process.
- The malolactic fermentation produces fruity, sweet and creamy aromas with a pronounced and complex acidity.
- Malolactic fermentation is an experimental process that only a few farms in the world can carry out.
- Lactic acid bacteria such as Lactobacillus are found in the coffee sludge Acidophilus , L. fermentum and L. plantarum .
- Lactic acid bacteria (LAB) feed on the sugar contained in the mucus and form lactic acid.
- Lactic acid aids in the breakdown of pectin, a complex carbohydrate found in high concentrations in coffee grounds.
- Lactic acid bacteria acidify, preserve and improve the taste, aroma and texture of some foods such as coffee. It also improves digestibility and helps preserve the products.
- The sugars found in coffee pulp, including hexoses (fructose, mannose, galactose and glucose), pentoses (ribose, arabinose and xylose) and polysaccharides (cellulose and pectin) are the main carbon and energy sources for the growth of lactic acid bacteria.
- In addition to producing lactic acid, lactic acid bacteria also produce enzymes that help break down complex proteins into free amino acids. This favors the development of some of the characteristics that make up the coffee’s sensory profile.
- Lactic acid inhibits the growth of bacteria that spoil coffee.
- Fermentation triggers a process of acidification and the breakdown of sugars. As the microorganisms feed on the sugars, producing organic acids, ethanol and carbon dioxide, the Brix (an indicator of sugar content) in the coffee grounds, which are eventually removed, decreases.
- By regulating oxygen in lactic acid fermentation, more lactic acid bacteria can multiply and others, such as B. aerobic bacteria, not.
- Temperature and humidity can speed up the fermentation process, which encourages the growth of fungi that can spoil the beans and cause off-flavors.
Benefits of Lactic Acid Fermentation
Introducing the right lactic acid bacteria strains into a fermentation can greatly improve the quality of the coffee. In fact, the cup rating of the coffee went from 80 to 88 points the first time it was used.
The interesting thing about this is the fact that lactic acid fermentation is a controllable process that can help develop differentiated coffees.
However, lactic fermentation is not beneficial for all types of coffee in different regions, as coffee processing depends on numerous variables:
- Quality of the substrate
- Ripeness and health of the fruit
- Environmental conditions
- Facility Conditions
- Control of the fermentation process
Difficulties in lactic acid fermentation
Performing malolactic fermentation can sometimes be difficult as there are many variables to consider throughout the process, e.g. B. Control of humidity and temperature.
All factors that influence coffee fermentation must be controlled, otherwise undesirable microorganisms can develop which promote propionic, formic, methane and butyric acid fermentation and lead to a very unpleasant coffee taste.
What does the future of lactic acid fermentation look like?
Many growers have focused on researching and developing their own fermentation protocols that give them control over all the factors that affect coffee quality.
Processing is one of the most important aspects of coffee production. Therefore, it must be performed very carefully and in a controlled manner, especially when dealing with experimental techniques.
However, experimental processing techniques such as lactic acid fermentation can be labor intensive and are therefore significantly more expensive than traditional methods.
Producers therefore need to be very aware of production costs before attempting experimental processing techniques, as these are generally riskier but potentially more economically viable. With this in mind, it is recommended to start in small batches.
On the other hand, traditional coffee drinkers will probably find it difficult to appreciate the different flavor profiles that can be achieved through malolactic fermentation. However, those who want to try new flavors are willing to pay higher prices to enjoy a cup of coffee with a different value.
Malolactic fermentation is an excellent alternative for producing high-quality coffee with a special taste.
It is evident that only a small percentage of growers undertake this experimental processing technique due to the high cost. In the field of coffee specialties, however, it is becoming increasingly popular.