Lucia Solis, a former winemaker and specialist in coffee fermentation currently based in Colombia, is one of the main voices fighting this narrative. In her podcast, Making Coffee with Lucia Solis, she questions some of the common myths we as an industry believe and repeat without really knowing the science behind them. In her work with mills and farmers, she constantly makes use of inoculation or adding external yeast to fermentation.

In the latest episode of her podcast, Lucia talks about adding fruit to the fermentation tank, chaptalization in wine and why it’s not "wrong" to add foreign microbes to coffee. As she is joining Algrano for a webinar on all things fermented on November 4th, we wanted to ask her what she makes of this whole shebang - and she is not very happy about it.

Fermentation is not a process in which flavours of foreign materials simply migrate to the coffee bean. It is rather a metabolic process in which microorganisms such as yeasts and bacteria degrade organic matter to produce energy. The flavour and aroma molecules we prize so much are the residue of this process. These molecules are the ones who migrate from the fermentation solution to the coffee bean and improve (or not) its cup profile. 

As all coffee post-harvest methods involve fermentation, every single coffee on Earth was “improved” by such molecules. Coffee enhanced by fermentation IS natural coffee, though we should probably avoid that word. So where is the problem? The issue might be the word “infusion”, which is used to indicate coffees with the addition of essential oils and fruit as if they were the same. They are not. However, the industry is putting everything in the same bag and we risk discouraging future experimentation. 

So what happens when you add fruit to the fermentation tank? Fruit won’t infuse the beans with its flavour/aroma as oil would with beans. It will rather help control the fermentation by providing sugar to the existing microbes. It also enriches the solution’s microbiota or changes its pH and therefore modifies the type of microbes that will be active during the fermentation. The change in flavour we observe in the cup is always an indirect consequence of the metabolic process.

“Adding fruits or other foreign materials can really help your fermentation”, she starts. “If you want to do an extended process or if you have to because you don’t have enough people to wash the coffee at the right time, giving the microbes something else to eat can buy you that time so they don’t degrade the coffee and compromise the bean structure long term. It’s not because it’s sexy. This is where the conversation on adulteration can get dicey because it can be a really good way to preserve the coffee. It’s just a tool producers can use if something goes wrong.” 

Adding bought yeast to coffee is also a great way to achieve consistency. “If you want to produce 10 containers of consistent coffee you should be inoculating. It’s kind of like washing your hands before surgery. It’s a no brainer. It’s what you do for security”, Lucia says.

Also, as acids are one of the residues of the process, fermentation can help prolong a coffee’s shelf-life. “Acid is key in preserving food in general. It brings stability and I also like it because it creates a structure that will withstand for a long period of time. You are creating body and fruity flavours but also more organic acids to preserve those flavours over time.” 

If you, as a buyer, are worried about the processing method of a coffee you bought, please don’t start by accusing the producer of adulteration. Though there might be cases, most producers know they depend on their reputation to sell coffee and making one good sale largely outweighs the risk of ruining one's name. Rather than buying coffee on flavour alone, develop relationships with farmers based on mutual trust and frank conversations. 

Strictly speaking, no producer will get sweeter coffees by fermenting them. “Fermentation is a breakdown of sugar. You are always losing it”, Lucia explains. But sweetness is not only about the real sugar content of the brew and our brains perceive sweetness even when it’s not really there. It's a fermentation paradox. “A lot of the time, sweetness gives you body and mouthfeel. Fermentation, especially with yeast, is really good at [replicating] that. It creates large compounds that increase the mouthfeel, so you can approximate sweetness if you have a really syrupy coffee. Fermentation also creates fruity or honey-like compounds so “your brain fills the gap”.

When coffee doesn't taste right, it's tempting to blame the fermentation process. It was either too long or not monitored well. But fermentation alone doesn’t offer enough information on quality. You also need to understand the drying process in more detail. “Drying can have more of an impact on quality and longevity than what we do at the fermentation tank”, Lucia starts. “We know that really high temperatures damage the seed's embryo, the structure and long-term viability of the coffee. So if the producers are drying on raised beds, are they covering the beans so they don’t get too hot? If they use a guardiola, are they just trusting the inlet temperature of the machine or are they measuring the temperature of the beans with a thermometer?”