Coffee treatment | what is the difference between carbon dioxide impregnation and anaerobic fermentation?

Without an in-depth study of biochemistry, we can assume that all coffee (with different treatments) has undergone a certain degree of fermentation.

Fully washed coffee must go through an artificial fermentation stage, in which coffee seeds are fermented after the peel and pulp are removed (sometimes the coffee seeds are placed in water, sometimes no water is used in the fermentation process)-and then cleaned, graded and dried. Re-soaking and washing the coffee after fermentation usually reduces the number of microbes, and the fermentation continues at this stage.

To be clear, even if oxygen exists in the environment of fermentation microorganisms, oxygen will not be used in a specific fermentation process. Saccharomyces cerevisiae can reproduce in a deoxidized environment at a slower rate than under aerobic conditions. With the continuous introduction of oxygen in the process of yeast fermentation, the yeast grows rapidly and multiplies faster. The yeast carries on aerobic respiration and produces carbon dioxide and water, but not alcohol. Fermented yeast in the absence of oxygen or lack of oxygen converts sugars into carbon dioxide and ethanol. Of course, there are many aerobic microbes that digest / decompose coffee fruit.

In the history of the production of washed coffee, the process / stage of soaking coffee to remove its skin-usually in open-air fermentation tanks, buckets, or even plastic bags-was called "fermentation". Its origin is only a method used by coffee farmers to remove mucus / pectin from coffee seeds. The resulting taste change, while important, was not the original intention of fermenting coffee.

Medium "anaerobic" fermentation has sprung up in the coffee industry. Usually, the coffee is peeled as usual, and then the coffee with pectin is placed in a sealed container (usually made of stainless steel) with a valve that allows the gas to be discharged. This fermentation method can extend the traditional fermentation time of 12-36 hours by several hours, sometimes even days. The types of microorganisms that can survive and actively participate in fermentation are limited by the amount of oxygen in the air, so they are likely to greatly change the final flavor of coffee. Anaerobic coffee has incredible and immediately recognizable flavors, such as gingerbread, cinnamon, licorice, bubble gum or boiled pears.

The main difference between anaerobic fermentation and carbon dioxide impregnation is that during carbon dioxide impregnation, coffee cherries are not peeled (in the whole fruit state) before entering the sealed container. (carbon dioxide impregnation is a term coined in the wine industry, in which the whole bunch of uncrushed grapes are put together in a barrel full of carbon dioxide (in an anoxic environment). The grape particles break and squeeze out juice. separate the grape juice and peel, and then add yeast to ferment. This process allows the use of neutral grape varieties to obtain aromatic wines, which are softer and fruity with distinct aromas of cherry, banana, bubblegum and cinnamon)

In carbon dioxide impregnation fermentation, first, put the coffee cherry in an airtight container with an one-way exhaust valve, which is very similar to the anaerobic method. Since the peel of coffee cherries is intact, it may take days or weeks to ferment. Different pressures in the tank produce different sugars and pectin for microbial decomposition. The coffee near the bottom of the closed container is squeezed by gravity, while the coffee cherry near the top of the closed container is not squeezed (its core is the intracellular fermentation and impregnation of coffee cherries under anaerobic conditions. there are three phenomena at the same time: intracellular fermentation of whole coffee cherry; alcohol fermentation caused by yeast; and impregnation of coffee cherry juice on the solid part of coffee cherry).