Chocolate is a wonderful treat any time of the year. But especially on Valentine's Day, when this traditional gift is tied up in bright red heart-shaped packages. Did you ever think about where chocolate is cultivated? Did you ever wonder why chocolate is expensive?
In its native rainforest habitat, cacao is a small tree found in the shady understory. It is grown in equatorial countries in Central America, South America, Africa, and Asia. The first part of cacao's botanical name—Theobroma cacao—means "food of the gods," denoting its culinary merit. Cacao trees grow from 20 to 40 feet tall. Cacao trees need several years of growth before reaching the age of the highest yield. The life span of a tree is approximately 25 years.
Figure 1. Cacao tree. Mandy L. Smith, Penn State
At maturity, the trunk and lower branches are adorned with clusters of thousands of tiny, half-inch, dangling star-shaped white blossoms that are nearly odorless to humans. Each tree has three variants of flowers. Fertilization occurs in only two of these types. The base of the flowers and stems contain microscopic nectaries. The small size and shape of the flower make pollination difficult for most insects. Thus, minute, pinhead-sized pollinators are needed to complete fertilization. These pollinators are a group of tiny midges in the Ceratopogonidae family. Most species in this family are biting midges that feed on warm-blooded animals.
Figure 2. An enlarged photo of the tiny midge responsible for cacao flower pollination. Chloe and Trevor Van Loon, CC BY-NC
Nevertheless, some species of midges are beneficial, and some are responsible for pollinating cacao. Cacao requires cross-pollination. The tiny midges feeding on the cacao nectar pick up the sticky pollen on minute hairs on their backs and transfer it from flower to flower. These chocolate midges are most active at dusk and dawn. This activity synchronizes with the flowers that begin to unfurl in the late afternoon and are completely open by dawn. Cacao can bloom all year, but the midges are seasonally abundant. Fertilization success varies because the flowers are receptive to pollinators for only one or two days. Despite year-round blooming and the midges carrying pollen from one flower to another, fertilization occurs in only 10 to 20 percent of flowers. Pennsylvania State University researchers found a gene that controls the flowering process and may also keep cacao trees free from disease. Hundreds of fertilized flowers on each tree grow into tiny pods. But within weeks, a natural process causes most pods to die back, allowing the tree to direct its energy into producing only 20 to 40 healthy pods containing 30 to 60 seeds or beans. Approximately 400 beans yield one pound of finished chocolate. So, one cacao tree produces only about nine pounds of chocolate per year.
Figure 3. A cross-section of a cacao pod exposing the beans and white interior. Photo: Glenn J. Koppel
An edible white pulp surrounds the beans in the pod. The beans are fermented in their country of origin. Fermentation naturally introduces other organisms, including yeasts and bacteria, to assist in obtaining our chocolate treat. The fermentation process, which can vary in the number of days, gives chocolate its distinctive aroma and flavor. After fermentation, the beans are shipped to the factory for the number of additional steps that will convert the beans into our favorite chocolate treat.
Commercial cacao growers operate plantations of varieties of cacao that are hardy and high producing. Smaller private operations grow cacao and produce chocolate in small batches. Regardless, they all require the pollinating capabilities of an exceptionally small fly. So, the next time you bite into a piece of chocolate, give thanks to a tiny midge!
To learn more about Penn State University's involvement in cacao research, visit the Cacao and Chocolate Research Network website.
Penn State is also involved in the Cacao for Peace initiative, where Colombian farmers are empowered to expand their cacao production through tools and resources.
