Shade Slope and Aspect effect on coffee quality

Shade Slope and Aspect effect on coffee quality

The most intense solar radiation reaches a plant growing in the tropics when the sun is directly overhead. As the Earth tilts, the solar intensity is reduced because the radiation is spread over a larger area.With some simple trigonometry, you can see that a shift in the angle of the sun of 60° reduces the available sunlight by approximately half. A coffee farm located on the Tropic of Capricorn will receive direct sunlight on the 21st of June. But by the 22nd of December, the angle of the sun will have shifted from 23° 26′ south to 23° 26′ north. this change results in direct sunlight being spread over roughly 36 percent more land area, reducing the intensity of light where it strikes the earth. However, the times when the sun is directly overhead roughly corresponds with the rainy season, which can result in significant cloud cover obscuring the sun’s rays in an effect known as albedo. Based on observations on Reunion Island, sited in the Indian Ocean, east of Madagascar, Bertrand et al., 2012 reported that solar radiation was negatively correlated with elevation, due to the frequent cloudy weather in the highlands, and positively correlated with temperature.’ In other words, increased solar radiation and temperature occurred in areas of lower elevation.

• During the season when the sun is directly overhead in the tropics, the combination of a lot of rain and a lot of light represents an intense growing phase for coffee plants. At this time of year, coffee plants tend to flower. Coffee farms located closer to the equator have some complexity regarding this seasonal fluctuation, however, because they can experience two rainy seasons per year. The biological clock of a coffee plant usually works on an annual cycle, but in some places on the equator (such as Colombia), some regions can have trees flowering while in a neighboring valley the farmers are harvesting.

Albedo

• Sunlight can reach a plant from below as well as from above. One means of this is by reflection from the Earth’s surface. In wine growing this is known as albedo. The extreme form of albedo comes from fresh snow, which will reflect over 80 percent of the solar radiation. High up, clouds in the stratosphere can reflect 70 percent of the solar radiation. Dark-colored, wet soil (typical of most coffee farms) will reflect only around 10 percent of the sun’s radiation. This is very similar to the amount that will be reflected from forest cover.The availability of sunlight is the major rate-limiting factor in the process of photosynthesis by coffee plants. For this reason, coffee farmers may thin the forest canopy as their plants mature.

Aspect

• Aspect refers to the orientation of a hillside relative to its compass bearing. It is an established principle of winemaking that the angle and orientation of a hillside can alter the flavour of a wine. The classic example of this is the difference between north- and south-facing slopes. If your coffee farm were on the Tropic of Capricorn in your rainy season, the sun will be aligned with the Tropic of Cancer. In this situation, a north-facing slope receives the most direct sunlight and a south-facing slope receives the least possible amount of light exposure.(Bertrand et al., 2012)concluded that the terroir of the coffee plant determined the sensory characteristics and chemical contents of its beans. They also found that the plant’s altitude and slope exposure created nuances in the sensory characteristics of coffees grown within a terroir.
• What’s the difference between Eastern or Western Aspect?

Plants with an east-facing aspect receive the first morning light, making them drier than plants with a west-facing aspect. The dew and rain begin to evaporate sooner in the day than they would on a west-facing aspect, so they have a head start. Plants with a west-facing aspect are usually warmer than those on a south-facing aspect, so ripening tends to occur more quickly. The last two decades have seen increases in the land area devoted to shade-grown coffee, but at the same time, non–shade-grown production has increased almost exponentially. ‘Shade-grown’ now describes around 24 percent of the land used for coffee. This amount is down from 43 percent in 1996. Yield-focused government incentives have been the driver for the widespread adoption of full-sun farming over the past two or three decades. Coffee research institutes created in the 1970s and 1980s , promoted the reduction or removal of shade cover.

• There is some controversy around the subject of shade. A disconnect exists between conservationists looking to maintain biodiversity and the viewpoint of yield-driven government incentives, aimed at increasing farmer prosperity. However, the literature points towards a happy medium here. Studies … have predominantly revealed that intermediate shade levels (approximately 35%–50%) produce the highest coffee yield, which is probably because of the balance maintained between optimal temperatures in shaded environments and optimal photosynthetic rates in unshaded environments … Because coffee yields are typically assessed independently of yield from timber, other crops, or ecosystem services, it may be difficult for governments and conservation institutes to weigh the benefits of diversified farming approaches. High yields don’t always equate with high quality.

Does Shade Grown Coffee Taste Better?

• it is clear that shade coverage is able to reduce average temperatures for coffee plants. using 45 percent shade netting found a significant difference between inner and outer leaf temperatures of coffee plants and a significant overall temperature drop. we measured differences of 4◦ C for inner leaves (measure from the trunk up to the sixth leaf) and 2◦ C for outer leaves. The same experiment accumulated sensory impressions of coffee grown under differing levels of shade cover. The chart below records the findings of their sensory panel. In addition, to testing full sun and shade, they also tested fruit load by removing a quarter and a half of the fruit from certain trees. The reason for this is that full sun plants tend to overbear and so the experiment sought to test if pruning could counteract this issue whilst still yielding good tasting coffee under full sun. The panel showed a clear preference for the shade-grown coffee over two growing seasons. A scientific study conducted on Reunion Island (the site of the Typica variety’s famous mutation into the Bourbon variety) collected sensory and chemical data from sixteen microclimates across the island. This research found a correlation between a cooler climate and positive sensory performance. Positive quality attributes such as acidity, fruity character and flavour quality were correlated and typical of coffees produced at cool climates.’
• One theory to explain why coffee may taste better in shade is the slower maturation of the fruit. In the case of the Reunion Island sensory trials, In a warmer micro-environment with high irradiance, coffee berries ripened faster in full sun than in shade. Therefore the harvest peak was delayed by about 1 month owing to shade. The slowed-down ripening process of coffee berries at higher elevations (lower air temperatures), or under shading, allows more time for complete bean filling Vast, yielding beans that are denser and far more intense in flavour than their neighbors grown at lower altitudes. Tropical climates are characterized by a reduced seasonal temperature variation. Where large changes in temperature do occur, altitude is usually the main modulating factor. But shade can give the farmer the ability to ‘micro-adjust’ the climate. The Reunion Island study confirmed that temperature during seed development has a major effect on the flavour of roasted coffee. The sensory trials found multiple correlations between coffee quality and lower temperatures. Coffees produced in regions with a cool climate (more elevated) are more acidic, have a better aroma quality and display fewer flavor defects than those produced in warmer regions (less elevated). Conversely, coffees grown under the hottest temperature conditions have lower acidity, lower aromatic quality, as well as the presence of green and earthy off-flavors … Aroma quality, acidity, fruitiness and overall quality were favored by cool climates, whilst the undesirable earthy and green tastes were increasingly present as the temperature increased. It therefore appears that the quality was weakest under warm climates.

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