By Emma Sage, Coffee Science Manager, SCAA
As the specialty coffee industry grows more concerned with sustainable practices at origin, we often find ourselves in conversations about shade-grown coffee. No one will argue that shade-grown coffee is less sustainable than growing coffee in full sun plantations, but what scientific information exists to support our tendency to support this practice? Perhaps shade matters more to some because they feel it influences the quality of the cup. What do we really know about these important issues? Justifiably, much research has been done on the ecological and economic impacts of shade-grown coffee. However, there is far less information available on how this influences the cup quality. Below, I highlight some of the most interesting points available in the scientific literature as I assess whether shade matters.
Differences in Shade-Cropping Systems
When we hear the term “shade-grown” coffee we may imagine a pristine ecosystem where coffee just happens to be planted and coffee farmers happen to be walking around in the woods picking beautifully ripe coffee. This romantic scene is rare if not completely absent from the coffee industry. However, there are varying degrees of forested coffee that are implemented at origin that we have to consider when thinking of buying shade-grown coffee (see Figure 1 for examples). Some cropping results in diverse and healthy ecosystems, others are an intricately planned and executed multi-cropping system. Some of these can qualify for special certifications, while others cannot.
1. Shade Matters Because It Positively Impacts the Environment
Shade-grown coffee can benefit the environment. It can do this in a variety of ways and at differing levels, but at the very least we can refer back to the bumper sticker in our hippie hall-mates dorm-room: “Trees are the Answer.” Trees take carbon dioxide out of the atmosphere and use it during photosynthesis. The carbon is then “fixed” or stored in long-lived plant tissues (such as the trunk, branches, or course roots of a tree). Therefore, trees mitigate greenhouse gases in the atmosphere, which impact climate change.
Trees can also fortify the ecosystem by providing it with structural and chemical resources. Structurally, trees provide a network of fine and coarse roots that can help prevent erosion. Some evidence suggests that tree roots do not even compete with coffee for resources because they utilize different areas in the soil (Schaller and others 2003). Chemically, trees can offer the soil much-needed nutrients from their fallen litter, especially certain species that can fix nitrogen from the air (Souza and others 2012; Romero-Alvarado and others 2002). Also, the shade from trees can offer a secondary benefit to the ecosystem by reducing understory and soil transpiration (i.e. water loss via evaporative forces).
There is a body of literature that supports the idea that when shade is added to a coffee growing system, the biodiversity of the ecosystem increases (Perfecto and others 1996; Romero-Alvarado et al. 2002; Soto-Pinto and others 2001). This is directly measureable through studies of species richness and taxonomic variation. We can quantify this through metrics created by conservation biologists. Of coarse, in certain situations there is also evidence that not all shaded coffee promotes biodiversity adequately (Perfecto and others 2005). However, when it comes down to it, biodiversity is intrinsically valuable. Ultimately, if one does not worry about species extinction and what it means for our planet and the human role in its future, then there is no reason that one must care about biodiversity. While many of us take this to heart, it is impossible to quantify the value of the concept because it is based on intrinsic value.
Finally, and importantly, shade can provide many environmental benefits to coffee. Generally, as shade trees tower over coffee plants they act as buffers to the coffee microclimate. Trees can act as insulators for the understory environment where coffee grows. In this way, they can both protect coffee from frost as well as cool the microclimate during very warm weather (Souza et al. 2012; Santos and others 2012). Another way that trees regulate microclimate conditions is through the inhibition of water loss from ecosystems. When this occurs, more water is left in the soil and is theoretically available to plants. One can imagine that this could be advantageous to coffee plants, which have to fight through the dry season to survive. However, there is some conflicting evidence in situations where trees did not seem to buffer ecosystem water loss (Cavatte and others 2012; van Kanten and Vaast 2006), possibly due to higher leaf area in shaded regions. Also, as mentioned above, trees and other shade plants in the ecosystem can provide additional nutrients for coffee via their litter (Souza et al. 2012; Dossa and others 2008). In these cases, especially when trees are nitrogen fixing and bring additional nitrogen into the soil, coffee plants generally need to be fertilized less than monocultures in sun (Romero-Alvarado et al. 2002). Finally, there is some evidence that coffee shade can prevent the spreading of certain weed species, which often thrive in full-sun environments (Eccardi and Sandalj 2002).
2. Shade Matters Because It May Impact Cup Quality
Can we taste advantages of shade-grown coffee? The answer seems to vary depending on individual situations. What we do know is that generally, the smaller coffee yield under shading is comprised of fewer, larger coffee fruits. Also, there is evidence that shade-grown coffee seeds have higher sugar and lipid contents than sun-grown coffee, which may increase the cup quality of coffees. Finally, there is some evidence that coffee grown in full sun is bitter in comparison with shade-grown coffee. However, there are also conflicting studies that have found no perceivable difference in quality. What is the problem here? We may be noticing a trend where the subjective sensory evaluation of coffee is getting in the way of consistent scientific results.
Multiple studies have confirmed that coffee plants acclimate to lower light by producing fewer productive coffee nodes per branch (Ricci and others 2011; Morais and others 2006). This is physiologically due to high growth rates and competition for carbohydrate resources among coffee fruits during heavy production (Vaast and others 2006). The theory is that these beans grow larger and more evenly over a longer period of time, which results in their higher quality. Many studies have documented a higher proportion of large beans under shade conditions (Geromel and others 2008; Steiman and others 2006; Somporn and others 2012; Muschler 2001; Bosselmann and others 2009; Vaast et al. 2006; Yadessa and others 2008). Some have related this directly to quality (Salva and others 2008). One theory to explain how this may translate to quality is that when they are roasted, larger and more consistently sized beans produce a more even roast and this translates to cup score.
Both sugars and lipids have been correlated with quality in past studies on shade-grown coffee (Alpizar and others 2004). However, the type of sugars seems to vary. One study found that in shade, coffee plants down-regulated the genes responsible for sucrose production, and instead produced more reducing sugars, which later react in the Maillard reaction during roasting (Geromel et al. 2008). They linked this to a one month delay in fruit ripening, and this has been confirmed by other research (Vaast et al. 2006), but ultimately depends on the level of shading. Other studies support the idea that reducing sugars are increased the most in moderately shaded environments, relative to sucrose (Somporn et al. 2012; Marraccini and others 2005). One study found that antioxidant content was linked to shaded growth conditions (Somporn et al. 2012). A few studies have even concluded that sun-grown coffee exhibits stronger bitterness than shade-grown coffee (Bosselmann et al. 2009; Vaast et al. 2006).
It is easy to imagine that shaded coffee at low altitudes may have the largest potential for impact on cup quality. This is because of the microclimatic changes that shade provides for coffee. In low-growing regions, lowering the average temperature (with shade) can mimic higher altitude conditions (sometimes dropping temperatures as much as 4°C), thus improving the cup quality (Avelino and others 2005; Vaast and others 2010b; Steiman and others 2008). Multiple studies have found that the acidity and body of brewed low-altitude coffee was improved by shading (Muschler 2001; Vaast et al. 2010b; Vaast et al. 2006). They suggested that this lower growing temperature produced a more uniform ripening of berries, which led to the better quality cup. Related to this is the possibility that shade at higher elevations could be detrimental to quality if the temperature range drops below what is ideal for coffee, but shade trees can also provide a buffer from frosts so this will depend on the individual microclimate. Some have found that shade had a negative impact on cup quality, including fragrance, acidity, body, and sweetness (Bosselmann et al. 2009; Vaast and others 2010a).
Some studies have not found an increase in cup quality in shade-growing conditions. Studies conducted in Hawaii determined that coffee shaded artificially and under tree cover had no difference in quality from sun-grown coffee (Steiman et al. 2006). One study even found that shade-grown coffee had lower cup quality in very wet conditions (Vaast et al. 2010a).
One Scientific Caveat:
Even if the evidence points to quality being higher in the slow-maturing, larger beans grown in shaded agricultural systems, we still do not fully understand how or why this occurs. It is important to note that we are assuming that slower fruit growth results in a higher quality cup. There may be a lot of industry information out there, but this has yet to be documented scientifically in coffee. Many experiments link shade to taste. However, unless we understand the biochemistry of fruit ripening time and how this directly effects the chemical composition of coffee seeds and link this to repeatable and consistent taste improvements, it is impossible to say with certainty what is going on.
Disadvantages and Drawbacks of Shade
Unfortunately, we run into the intrinsic value of shade-grown coffee again here. What is it worth to us in consuming countries? What is it worth to coffee farmers at origin? In many situations, shade lowers coffee yield (Steiman et al. 2006; Vaast et al. 2006; Morais et al. 2006), and delays ripening (Muschler 2001; Vaast et al. 2006; Ricci et al. 2011). In some circumstances, trees have even been found to compete with coffee for resources, which may further reduce the yield of shade-grown coffee (Haggar and others 2011). Also, in a very wet year shade can promote the growth of moisture-loving fungi, which in extreme circumstances can lower production for years to come. Another important disadvantage of shade-growing coffee at origin is that this method of agroforestry can be more labor intensive. These issues are far more critical to coffee producers than consumers. This means that unless the coffee is very high quality, farmers may get less money per hectare of coffee farm. Both of these disadvantages lead to coffee producers receiving a lower profit for their product. Fortunately, some farms that use agroforestry can benefit from pricing incentives offered by certification programs.
It is important to note that certain research has documented higher yields (Somporn et al. 2012; Santos et al. 2012; Muschler 2001) or no change in yield (Romero-Alvarado et al. 2002; Muschler 2001; Ricci et al. 2011) under shade-growing conditions. The explanations behind these situations often include additional resources provided by shade trees, such as water conservation that proved advantageous during a particular year.
Ultimately, shade-grown coffee must be assessed at a case-level basis to determine the system of shade-cropping as well as any environmental impacts, good or bad, that it has on the ecosystem. Coffee buyers will be most able to assess this in transparent relationship and direct-trade situations. Of course, this is easiest when they know their importer, exporter or farmer. In the end, it is up to the entire specialty coffee industry to make sure that the coffee we buy is sustainably grown. Certifications such as the Rainforest Alliance, Smithsonian Bird Friendly®, Utz, and Organics have been global contributors to agricultural sustainability through their certification programs, and are invaluable systems for providing coffee producers adequate incentives.
As of today, we have some evidence that shade can positively impact the cup quality of coffee. However, in producing situations it is very difficult for even the most experienced coffee buyer to differentiate how environmental variables influence a cup. In the future, it is a goal of World Coffee Research, supported by the SCAA, to develop a coffee cup quality evaluation method that is precise, rapid and cost-effective and is in harmony and accord with most of the coffee industry and consumer representatives. This will be a large step in the process of clearly linking quality factors with aspects of terroir, including shade.
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Emma Sage is the new SCAA Coffee Science Manager. Before moving into the coffee industry, she completed degrees in ecology and botany, and dabbled in the wine industry. She is excited to learn all there is to know about the science of coffee (and more importantly, to share it with you).