Explanation on the fermentation mode of raw coffee beans: the difference between dry fermentation and wet fermentation and the scope of application

For professional baristas, please follow the coffee workshop (Wechat official account cafe_style)

Does the fermented taste of coffee beans indicate poor quality?

The fermentation of raw coffee beans can be divided into dry type and wet type.

Dry fermentation is subdivided into Brazilian style, Yemeni style and Sino-American style. (it's really complicated.)

In the case of Brazilian beans, there is a "dry fermentation" because of the local lack of water.

Is to remove the peel first, and then put part of the pericarp into the fermentation tank.

Use the enzymes in the pericarp to play a role

The advantage is that it will have the sweet aroma of syrup, while medium baking will have nutty and cocoa aromas.

The disadvantage is that if it is not handled properly, it may be accompanied by earthy and musty smell.

If there are too many defective beans that pollute the aroma, the quality of coffee will be affected naturally.

It will be beaten to the commercial bean.

But for Yemeni mocha and kabou,

Dry fermentation produces a soft and palatable aroma like ripe dried fruit and wine.

This is because the humidity in Yemen is drier than in Brazil.

However, the dry fermentation technology of Central American countries such as Panama is more advanced than that of Brazil.

The fermentation process strictly monitors the enzyme concentration, the content of coffee pulp and the temperature in the fermentation tank, etc.

Reduce the bad flavor that may be produced in the fermentation process.

Yemeni Moka. Jpg

But some producing areas are inherently unsuitable for dry fermentation (for example, Colombia)

So wet fermentation is used in these areas.

However, some people always think that the taste of wet fermentation is not much different from that of washing treatment.

The flavor is a little too clean.

And wet fermentation has its drawbacks.

Food spoilage bacteria such as butyric acid bacteria may appear in the sink, resulting in sour taste.

If wet fermentation is handled well, it will show the aroma of coffee.

If it is not handled properly, it will be the bad taste of the fruit!

This phenomenon is quite common in wet fermentation or honey treatment.

The pros and cons are not a matter of handling methods, but quality control is the key.

That's why the cup test is important.

The quality control of coffee beans is from planting, harvesting, processing to export, transportation, baking and packaging.

The extreme requirements of each link can achieve "boutique coffee".

Dry fermentation and its flavor

"after we remove the pulp, we put the coffee with endocarp in the fermentation tank, and the fermentation promotes the sweetness, chocolate and fruit flavor of the coffee." but one of the challenges of fermentation is temperature control. Since temperature can affect the degree of fermentation, it will also negatively affect the stability and flavor of the process.

Effect of temperature on dry fermentation, source: Sasa Sestic

The diagram on the left side of the dotted line above shows that we ferment the coffee at an average temperature of 16 degrees for 24 hours. The coffee tastes great and the flavor is well balanced.

The right side of the image above represents fermentation at a temperature of 26 degrees for 24 hours, with marked pink blocks, which can occur when the fermentation is too long, and alcoholic acids dominate the fermentation, resulting in excessive acetic acid, dryness and metallic taste.

Wet fermentation and its flavor

You may have heard someone describe wet fermentation as double washing, double fermentation, Kenyan washing, etc., which is common in East African countries and is famous for its clean and clear flavor, but Sasa describes this treatment as adding flavor to the cup.

"when we remove the pulp and put the coffee with endocarp into the water, the water will help prolong the fermentation time, resulting in a softer mellow thickness, rich acidity and more elegant flavor characteristics of the coffee."

Fermentation tank built by the inspection program in Ethiopia, source: Project Origin

Of course, this does not mean that the treatment is not challenging. Sasa mentioned that temperature and water quality can also affect the results.

Sasa: "A few years ago, I did an experiment with Raul Riviera, the owner of Santa Rosa in El Salvador. We used Rain Water instead of spring water to ferment. Rain Water would absorb a lot of fruit flavor and sugar from the coffee fruit. As a result, the cup test score was reduced by five points. The coffee tasted insipid and had no distinct flavor. The effects of the water used for fermentation still need to be studied. "