The goal of the Merit 101 series is to help educate all levels of coffee enthusiasts who want to learn more about who we are at Merit, as well as the many aspects of coffee.

A special thanks to Dr. Taya Brown for her help on this post. Taya is a coffee horticulturist whose research connects agronomy and and sociocultural practices in Yepocapa, Guatemala. Learn more about her work with the Del Fuego project here.  

Part II: Ecology

Terroir describes the unique flavor profile connected to a place where a crop grows, or where a culinary process (like fermentation) unfolds.

In our first installment, we explored the effect of the physical environment on coffee quality. Here we’ll transition into the biological environment’s effects on quality. Within our ideal climate, soil and ecology have the largest influence on plant health. The overall trend is simple: slow, healthy growth produces more complex coffee. Specific flavors may come into play in the microecology of fermentation.

Soil

Arabica coffee grows in a wide range of soils, from the sandy slopes of volcanoes in central America to red clay soils in highland Kenya. Coffee plants need plenty of water, but also soil with good drainage and thus, lots of oxygen.

Then, there’s nutrition. It’s not enough for a soil to have a good starting cocktail of key macronutrients like nitrogen, phosphorus, and potassium. Without a minimum level of ANY micronutrient (like zinc or cobalt), the plant can’t unlock its full potential. This is called the law of the minimum, usually explained with the barrel analogy below.

The waterline represents the plant’s yield and quality. Each wooden segment represents a specific nutrient, macro and micro.  When a segment doesn’t reach the top of the barrel (a nutrient deficiency), the barrel can only hold water to that level. Similarly, plants are limited in their potential by ANY nutrient deficiency.

To naturally and cheaply achieve this goldilocks environment, we need organic material (OM). Organic as in “derived from living matter,” this describes a layer of leaves, plant material, and animal byproducts - the rich, soft stuff you’ll find on a forest floor. Such a feast draws worms and other decomposers to the party (and if they don’t come naturally, farmers will bring them in). These creatures break down OM into baseline minerals that the plant can consume, leaving behind sticky mucilage that binds small soil particles together. The entire process creates a substance called humus (pronounced hue-mus).

Organic Material transforming into rich humus. San Jose Lourdes, Cajamarca, Peru.

Humus is like a dark, spongy chocolate cake for the plants—lots of space for air, but still moist, and full of fuel. It also buffers the variance in pH, creating a more stable environment for nutrient uptake. The availability of nutrients and presence of decomposing bacteria draws in other fungi, yeast, and microorganisms, which creates a thriving soil ecology.

How can you taste nutrition in coffee?  Defects known as quakers are a great example. Just like humans, if a plant is under extra stress (from climate change, disease, etc.), it burns more energy. When a coffee plant can’t eat enough for all the work it’s doing, its becomes weak. Its body has to prioritize where the energy goes, and some developing seeds will get less nutrition than others.

Yellowish "quakers" stand out against fully caramelized, roasted coffee.

These seeds grow less densely, leading to oat-like (get it? Quaker?) and cereal flavors, thin body, and a soapy finish in the final cup. You can even see them in roasted coffee: quakers look much lighter than normal beans because they lack the compounds that turn brown in the roasting process.

Above Ground Ecology

Coffee plants growing under a natural shade canopy. Bita Genet, Kaffa, Ethiopia.

If organic material is the basis for great soil and micro-fauna, shade trees are the foundation of biodiversity on a macro level. The entire ecosystem is a holistic,living entity that reinforces itself as it grows. Improving the health of any aspect of this environment adds resilience against major shifts or shocks and thus creates stronger plants and better cup quality.

The ideal role for coffee is as a mid-level shrub, with roots in the soil and protection under a higher forest canopy. The tallest trees in this ecosystem (which we’ll refer to as shade trees) dapple light on the forest floor. At the right density, this level of light allows coffee plants to grow slowly but inhibits weeds and grasses that compete for water or nutrients. Heavier shade also makes the seeds grow more densely. The space between the top of the canopy and the coffee plants acts like a layer of insulation, cocooning the coffee in a stable range of temperature and humidity. The roots of shade trees anchor the soil to prevent erosion. And, of course, they’re deeply connected to OM: shade trees create organic material as they shed leaves and branches.

These benefits appeal to other plants and animals as well. Such a cozy habitat invites larger insects, spiders, birds, and mammals. Combined with beneficial microorganisms in the OM, they create a strong defense against coffee’s major pests and diseases. On the flip side, a lack of shade can stress the plants and inhibit nutrition, contributing to the quaker defect. 

Leguminous Inga trees interspersed among coffee plants. El Socorro, Chimaltenango, Guatemala.

The best shade trees and cover crops do double-duty by fixing key elements in the soil. For example, leguminous plants have special nodules in their roots that team up with rhizobacteria to make nitrogen more available for coffee plants. Nitrogen fixation is critical for any agriculture; without it, no life can grow.

Producers have some favorite plants and animals to pair with coffee. Inga trees offer great shade, and their leguminous roots enhance the soil’s nitrogen. The Grevillea genus of trees acts as a great wind-break while providing an excellent home for birds. Farmers often establish beehives within their coffee farm since the bees’ pollination hugely enhances overall biodiversity, strengthening the whole system.

Coffee and honey, both harvested from the same farm. Jaén, Peru.

In Fermentation

A diverse ecology also plays a part in coffee fermentation. The fermentation environment—whether it be de-pulped cherries in a tank or whole cherries drying in the sun—creates a complex microecology all its own. Unlike a lot of commercial fermentation, most coffee is fermented using whatever wild microbes are on the cherry skin or in this. Richer biodiversity on the farm will translate to the fermentation ecosystem. This system has a massive influence on the complex aromatics that are imparted in fermentation, both because of the species of microbes around and the way they interact with each other. 

Pickers pre-sort cherries they've just brought in from the field. With every cherry comes wild yeast and other microbes from the farm's environment, which affect the outcome of fermentation. El Soccoro, Chimaltenango, Guatemala.

A Note on Intercropping

Thoughtful producers often practice intercropping. By building an ecology with multiple cultivated crops, they can secure their personal food supply and generate more consistent income. When done right, this makes coffee a more sustainable enterprise both financially and environmentally.

Coffee, cardamom, and vanilla seedlings in a nursery for an edible forestry project. All three plants will grow in concord with each other on the same plot. Sierra Sur, Oaxaca, Mexico.

To sum it up: soil and above-ground ecology have a more general effect on coffee quality, but they are a crucial reason why certain areas have gained renown.