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Q & A: Dry Fermenting?

Q & A: Dry Fermenting?
8/29/19

Q: (V.) Hi! I was wondering if I could get more info or clarification on the processing of “Papua New Guinea Kainantu Sero”. The specs on SM say it's washed but the farm notes mention dry-fermenting for 36 hours?
"Mr. Sero dry ferments his coffee for 36 hours, perhaps lending to the fruited characteristics found in the cup."

A: (Tom) Hi V. Thanks for the question: so washed coffee (wet-process) is fermented as part of the procedure …though there is some “machine washed” coffee that might not be fermented. Fermentation breaks down the fruit flesh (mucilage) layer so it can be washed away. It’s like a plum - like the flesh part, when it doesn’t separate from the seed. Fermentation time depends a lot on temperature in the area so can be as short as 8 hours but at colder higher altitudes can be as long as 36 hours or even 72 hours. After it is fermented, the coffee is washed down the channels and water and physical agitation remove the fruity mucilage layer.
So the coffee is wet processed and it is fermented 36 hours. Long fermentation times can lend a little fruit to the cup, but not always. Anyway, the Specs and review are both right. Sorry if any of this is stuff you already know but just wanted to lay it all out!

V: Thanks for clarifying that Tom.  But there’s still a contradiction: Your "Specs" says it’s Wet Process and Patio Sun-dried. The Farm Notes say, "Mr. Sero dry ferments his coffee for 36 hours, perhaps lending to the fruited characteristics found in the cup. As you point out below, if the coffee were Wet Processed then I would expect that the notes would not say “Mr. Sero dry ferments his coffee for 36 hours.”

Tom: Ah - Okay I understand the question now. Your question makes a lot of sense and I understand completely: How can wet-process coffee have dry-fermentation? We used the term “Dry fermentation” in that review, which has nothing to do with dry-process ... what we mean is that the pulped coffee (coffee with the skin removed) is fermented in a tank without additional water... dry.
I see we made that distinction in the review without fully explaining it! In contrast there are places that ferment under water, that is, adding water to the tank after they pulp the coffee into it, submerging the coffee. So the review is correct but doesn’t explain what dry fermentation is...
Actually I would say most coffee that is wet-processed is fermented without being submerged in water to do so . So most is dry-fermented. There's a bunch more to say about this but I seem to be overshooting the target when it comes to question-answering lately!
I'll add some photos from my trips that illustrate the difference, and I hope that helps!

  1. Q & A: Dry Fermenting?

    Nicaragua - Buenos Aires Wet Mill La Camapana

    Dry fermentation in tiled tanks, with some residual fruit skins. Ocotal Nicaragua. In this warm climate fermentation can be as little as 8 hours.

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  2. Q & A: Dry Fermenting?

    Underwater "anaerobic" Fermentation at Tade GG Station

    Tesfaye ferments under water for up to 72 hours, and evidence of the biological reaction is the film on the surface. Anaerobic / underwater fermentation always takes longer than "dry fermentation".

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  3. Q & A: Dry Fermenting?

    Adame Gorogota Cooperative, Wenago Ethiopia

    Tekele tests parchment to see if it is ready to wash in the channels and dry. This is submerged / underwater fermtation, which some call anaerobic. It's typical in Sidama zone.

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  4. Q & A: Dry Fermenting?

    Limmu Kossa Farm

    At Limmu Kossa farm. They pulp the coffee, then ferment 12 hours dry (not under water) , then demucilage, then soak the coffee before it goes to the drying beds. The water added after fermentation is to wash the coffee into the channel and demucilager. This is an unusual method, to ferment, then demucilage the coffee,

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