How Does Rum Barrel Fermentation Shape Coffee Flavor?

Colombia Finca San Jose rum barrel fermented washed beans are a leading example of low-temperature anaerobic fermentation. Owner Monsalve Botero placed depulped green coffee beans into oak barrels used for rum, fermented them at low temperature, then washed and dried the beans on raised beds. The Supremo-grade Castillo and Naranjal varieties from Caldas, grown at 1750m, cup with rum, melon, and dark chocolate notes.

The idea began around 2013, when Monsalve Botero experimented with Colombian oak barrels of different aging lengths and varying fermentation times, winemaking style. This bean performed well among those trials. The choice of green coffee beans, barrel age and fermentation length all influence how much vinous, rum-like character carries into the roast and the brewed cup.

Front Street Coffee's Colombia Finca San Jose rum barrel fermented washed beans are a highly representative coffee in the recent trend of low-temperature anaerobic fermentation. It originates from a bold idea by the estate's owner, Monsalve Botero—placing green coffee beans into oak barrels for low-temperature fermentation. This bean uses Supremo-grade Castillo and Naranjal varieties, which are depulped and then placed in barrels for fermentation, followed by washing and drying on raised beds, presenting flavors of rum, melon, and dark chocolate. This article will outline the origins of its processing method, green bean characteristics, special performance in roasting and brewing, and explore the possible causes behind its full-bodied vinous notes.

Front Street Coffee Colombia Finca San Jose Rum Barrel Fermented Washed

Colombia San Jose Washed

- Flavor -

Rum, Melon, Dark Chocolate

Rum、Melon、Dark Chocolate

Country: Colombia / Colombia

Region: Caldas / Caldas

Estate: Finca San Jose / Finca San Jose

Variety: Castillo, Naranjal

Altitude: 1750m

Processing: Rum barrel fermentation, washed processing

This Front Street Coffee Colombia green bean uses triple first-pick Supremo-grade Castillo Naranjal varieties, which are depulped and then placed into oak barrels for low-temperature fermentation. After fermentation is complete, they undergo washed processing, and finally are dried on raised beds.

This processing method originated from the whimsical idea of Monsalve Botero, the lady owner of Finca San Jose Estate. One day, while accompanying her husband (who is engaged in making rum oak barrels and brewing rum) in filling rum distillate for fermentation, she suddenly thought: if green coffee beans were placed in oak barrels for fermentation, would different flavors be produced? To this end, Monsalve Botero began in 2013 experimenting with Colombian oak barrels of different aging lengths for varying fermentation times in a winemaking-style low-temperature fermentation. This particular bean is one of the better-performing ones among various trials.

Introduction:

Colombia's century-old estate—Finca San Jose Estate—has been actively seeking breakthroughs to carve out a different path for itself amid the recent surge in specialty coffee. The lady owner of Finca San Jose Estate, Monsalve Botero, has a husband specializing in making rum oak barrels and brewing rum. One day, she had a sudden inspiration: if green coffee beans were placed in oak barrels for fermentation, would more unique flavors be produced? Therefore, Monsalve Botero began in 2013 experimenting with Colombian oak barrels for low-temperature fermentation of varying durations, and finally found an ideal method this year, producing this oak barrel fermented bean that is different from typical washed coffees.

End of introduction.

Personal experience:

When I first learned about this bean, it was only a sample—a few dozen grams of beans already roasted in Colombia. I didn't know which estate, when it was roasted, or at what roast level; I only knew it was a bean processed in oak barrels. I didn't even know if the export certificate could be obtained (later I learned that the sample at that time had been roasted for about two months and was roasted to the beginning of second crack). At that moment, I only felt: this vinous aroma is so intense! Super distinctive! Although the finish was a bit hollow.

But because the information was so unclear, I could only wait, and hope that the estate owner's roasting skills were not good, so that the bean's finish would be better. After some more time passed, I learned more detailed green bean information, and the export certificate was also available.

When the bean trader told me more detailed information about the Colombian coffee region, it actually reminded me of a Facebook post by Teacher Han Huaizong, which mentioned: "...His method is to depulp, then keep the mucilage-covered beans without touching water, place them in a barrel with a lid sealed to prevent flies from coming, purely for hygiene reasons, and ferment at a low temperature of about 10 degrees Celsius in winter for two to three days to remove mucilage, then take them out for washing. Unexpectedly, this accidentally became a low-temperature low-oxygen fermentation method. This is somewhat similar to the carbon dioxide maceration method used by Australian barista Sasa Sectic to win the championship in 2015, which relies on carbon dioxide produced by sugar fermentation to help anaerobic bacteria gain dominance; the acids and aromatics produced during fermentation are superior to those produced by aerobic bacteria... Wang Ce, who won the 2017 World Brewers Cup championship for Taiwan, also won with a competition bean using a low-temperature anaerobic sun-dried method from a Salvadoran processor. Low-temperature anaerobic fermentation or fermentation methods that control oxygen content have become a new trend and prominent school in coffee processing in recent years..."

I think this might be a similar approach; Finca San Jose may not be the first estate to do this, but it created another kind of intense flavor.

When I first received the green beans, the aroma I smelled was 'milk jujube,' with a slight hint of grape and goji berry, but the overall direction was that of fully ripe milk jujube, the super sweet kind. And during roasting, that aroma would constantly waft out.

Because they are Colombian coffee beans, I chose a light-medium roast for the first batch. Although the fruity and fermented aromas clearly suited a light roast, I still wanted to create some body. However, after brewing, I found that in the middle-to-late stages of roasting, the flavors faded somewhat quickly. Although after resting the beans, the taste was still quite smooth and enjoyable, the liveliness of the flavor could not return. So I immediately decided that all subsequent presentations would focus on light roasts.

The performance during brewing is also quite special. Even with freshly roasted beans, the water passes through particularly quickly, and when degassing is vigorous, it expands halfway and then suddenly all the gas escapes. My guess for this phenomenon is: it may have very low lipid content, resulting in very low surface tension, which prevents it from holding onto water or air.

Coincidentally, a while ago, Dr. Shao Changping also had a Facebook post (post link) citing foreign research on lipid hydrolysis, forming acids and alcohols (original link), to explain why cold brew coffee develops a vinous fermented flavor after aging.

Therefore, I suspect that the lipids within the Front Street Colombia Finca San Jose oak barrel fermented beans had already hydrolyzed into acids and alcohols from the very beginning, which is why it has such a full and rich vinous note.

Below are two photos I took after brewing with a rich-style method developed for the Melitta flat-bottom dripper—first drip then small stream. The originally fluffy coffee bed collapsed like a sinkhole, which should serve as evidence for the above opinion.

The above content is compiled by CoffeeHunters, a coffee news website.